ALARIO-FRANCO INTERNATIONAL SYMPOSIUM (2ND INTL SYMP ON SOLID STATE CHEMISTRY FOR APPLICATIONS & SUSTAINABLE DEVELOPMENT)
Editors: F. Kongoli, F. Marquis, S. Kalogirou, B. Raveau, A. Tressaud, H. Kageyama, A. Varez, R. Martins.

The final prices of a LIB depend to a large extent on the materials used and the manufacturing process. The reduction of non-active materials (50% of battery weight) (Al and Cu current collectors, separators),, plays a fundamental role in reducing costs for both the production process and the final device [1]. On the other hand, the cathode thickness currently limits the total energy density and power of LIBs. One option to address this limitation is to increase the cathode thickness and consequently balancing with a thicker anode. In this way, the active materials volume ratio in the cell increases (the electrodes areal and volume capacities grow), achieving higher specific energy and specific power per weight and per volume [2].
Commercially available batteries are usually composed by cylindrical, coin, prismatic or pouch cells. Therefore, the development of new processing technologies is needed to design more complex geometries that could fit specific cell designs. In this context, additive manufacturing (AM) technologies have shown their potential for the design of 3D objects with non-conventional geometries and reduce number of produced parts and have been recently applied to different energy devices [3]. Although AM technology has not been used for commercial batteries, its use can contribute to the optimization of the final design of the devices, allowing the use of batteries with more complex shapes.
In this work, Fused Filament Fabrication (FFF) is proposed as a cheap, affordable and solvent-free processing method alternative to conventional electrode manufacturing for Li-ion batteries, which allows developing additive-free ceramic electrodes with enhanced energy density. The production of thick ceramic LiCoO2 (LCO) electrodes using a desktop 3D-printing was developed as an alternative to conventional electrode manufacturing for Li-ion batteries. Firstly, the filament formulation based on LCO powders and a sacrificial polymers blend, is optimized in order to achieve the suitable features (viscosity, flexibility and mechanical consistency) to be used in a conventional desktop 3-D printing. Printing parameters were optimized to produce defect-free bodies with coin geometry (12 mm diameter and 230-850 µm thickness). Thermal debinding and sintering were studied in order to obtain all ceramic LCO electrodes with adequate porosity. The additive-free sintered electrodes (850 µm thickness) have enhanced areal and volumetric capacities (up to 28 mA·h·cm-2 and 354 mA·h·cm-3) due to their extremely high mass loading (up to 285 mg·cm-2). Thus, the Li//LCO half-cell delivered an energy density of 1310 W·h·L-1. The ceramic nature of the electrode permits the use of a thin film of paint gold as current collector, reducing considerably the polarization of thick electrodes. Thus, the whole manufacturing process developed in this work is a complete solvent-free method to produce tuneable shape electrodes with enhanced energy density, opening the door for the manufacturing of high-density batteries with complex geometries and easily recyclable.

This paper will cover the evolution of the idea of ‘Entropy’ from the idea of temperature(1) and engines to the Second Law of Thermodynamics which has churned out scientific paradigms and raised philosophical questions; then the origin of the ‘entropy’ as a classical thermodynamics property by Rudolph Clausius in 1865(2), its statistical thermodynamical interpretation by Ludwig Boltzmann in 1877(3), and the using of ‘entropy’ in the Information Theory in 1948 by Claude Shannon(4), opening up its application and interpretation in newer fields – which seems to be an ongoing process.
Application of the ‘entropy’ concept has been in all branches of Engineering (particularly Mechanical, Chemical and Metallurgical), Physics (from Classical to Molecular)(5), Physical Chemistry(6), recently in Information Theory, very recently in Quantum Computing, Reverse Computing. Also, there is the process of entropy generation and its minimization ideas and their application in the Design of Nature by Bejan(7). A Mosaic of Ideas, entropy concept has remained enigma in the field of History of Science.
The paper will trace the application of the phenomena of rise in temperature and the engine concept in the Hellenistic period (Galen & Hero) to Renaissance Europe (Galileo) to the evolution of Steam Engine, the 2nd Law of Thermodynamics, Chemistry and Information Theory.
In India, around 1100 AD, the perpetual motion machine is mentioned but not ‘entropy’, though ‘transformation’ (the Greek word’s meaning) has been a widely discussed topic in Philosophy and Chemistry in India(8).
This review will be useful not only to understand ‘entropy’ but also to show the universal spread of the nature of Science and Technology. This seems to be a path along which we travel, more than a ‘point property’.
Keywords: Second Law, entropy, entropy generation, disorder of molecules, information theory, thermal equilibrium.

The beginning of my scientific & academic career my first challenge, started in fact, in the 4th year undergraduate when, under the direction of my supervisor, Professor A. Mata Arjona, I did build the technical equipment for the thermal treatments of solid samples in vacuum and the measurement of their porous texture. This led to my thesis work concerning the structural & textural study of porous solids (The porous texture of Aluminium Phosphate Gels. Univ. Complutense-Serie A-Nº 110; 1970-In Spanish¡). Interestingly, these materials and studies are now relevant, more than 45 years later, when ALPO is being studied as absorbent of CO2 and water from the atmosphere fighting with drought and climate change (B.D. Yuhas et al Chem.Mater.2018,30, 583-586 and references therein). This equipment was then used for a number of years by mine and other doctoral students: my first achievement¡
I did my postdocs in the UK, learned various techniques as TEM, ED, ESCA.…and more about materials synthesis. Back in Spain, in 1976, I became Chemistry Professor at 34 years of age; another landmark in Spanish Universities-
By 1974, I created the first Solid-State Chemistry group -by then a relatively new subject- and after setting up an Electron Microscopy center and a High Pressure Synthesis lab -a technique that I did get to know in the CNRS & INPG in Grenoble France, I did mentor various “collections” of undergrads (around 70) and graduate (some foreign) students – to arrive to have, along the years, more than 25 D.Sc. disciples, 15 of which are today University full professors and have created their own schools, in Spain and other places. One can estimate that around 200 scientists have participated in and benefited of the activities of this innovative scientific school.
Simultaneously I did develop and implemented in the Chemistry Curricula Solid- State Chemistry as a discipline in the degrees of Chemistry and Materials Science & Engineering, that is now used in many Spanish Science Faculties. In the Academic career, I have been successively Professor, Dean of Faculty, Director of Summer School, member of the Royal Academy of Sciences of Spain, -of which I have been President- Also honorary member of Colombia and Argentina and of various other national and international scientific organizations, like EURASC or the university of Wales.

The work on my D.Sc thesis consisted in a study of the textural and structural developments in the thermal treatments of Aluminum Phosphate hydrated gels. Immediately after, in my fist postdoc I discovered the interconversion between CrO2 & CrOOH in different atmospheres and I also performed a textural analysis that was followed in ulterior thesis back in Spain where we did study the diffusion coefficient of H in this process. A plethora of oxyhydroxides & hydroxides was than prepared and deeply studied structurally and microstructurally. In my second postdoc we looked at extended defects in CrO2 and found a new family of Crystallographic Shear (CS) Phases, a subject of great interest at the time -mid 70’s.; simultaneously we made a deep study by means of Photoelectron Spectroscopy, in the first equipment available commercially, of chromium oxides and confirmed Goodenough Model for Rutile type dioxides.
Back to Spain in my then starting research group (1973-4), we dedicated our efforts, mostly, but not exclusively, to the synthesis and characterization (structure, microstructure, electric, magnetic, thermal) properties we did extend the studies on CS in various system and the structure/properties relations and its evolution with temperature in TM oxides obtained at RP/HT and, specially at HP & HT in the HP-Laboratory that we did set up -first one in Spain and one of the very few in Europe by then- more than 15 external groups have benefitted of this innovative laboratory. Also, the deep microstructural and spectroscopic characterization was performed in the Electron Microscopy “Luis Bru Center” that I founded at UCM. Work on Perovskites followed and we did publish the first Spanish paper in Physical Sciences in Nature (1977) concerning extended defects in bulk SrTiO3 and later on its surface (SS Sciences 2009).
Continuing on perovskite related work we did launch an extensive collaboration wit three French laboratories: Two in Grenoble and one in Bordeaux, where we did introduce the electron microscopy and diffraction techniques. In this last case, we demonstrated the phenomenon of three-dimensional microdomains associated to non-stoichiometry associated to Red-Ox processes in Ca-La Ferrites.
In late 1986, the extraordinary phenomenon of HTSC, was discovered and we were the first group in Spain to obtain YBCO derived materials, such as REBa2Cu3O7-x (Solid State Comm 1987) still the Highest Tc (=96.5 K in the case Re <> Sm) for an YBCO superconductor. Shortly after we did prepare the whole family with most of the Rare Earths and distributed samples of the in various laboratories, including the one of Cardona in Stuttgart¡
For its part in Grenoble, we had a verry strong collaboration in those HTSC cuprates in which we established the existence of the “intermediate phase” Y2Ba4Cu6O13 (Solid State.Comm.65, 283-6, (81988/1/1) and obtained “A new family of cupro-carbonates” (Physica C, 1-2, 52-6(1994) & Physica C,235-240, 975-6 (1994). Which still displays the High Tc record for non-toxic materials:117K at room pressure.
On the other hand, in Madrid, our work has also demonstrated a novel Red/Ox mechanism in the oxidation –and concomitantly a very marked increase in Tc- of cuprates having two different transition metals: Mo0.3Cu0.7Sr2RECu2O7+x (Dalton Transactions: 44(23) 10795- 805(2015)).
A few additional examples of our more recent work in superconducting and other materials will be presented in the lecture.

Solid-state inorganic fluorides are present today as components in many advanced technologies, including energy storage and conversion, microphotonics, fluorescent chemical sensors, solid-state lasers, nonlinear optics, nuclear cycle, superhydrophobic coatings, etc. Most of these outstanding properties can be correlated to the exceptional electronic properties of element fluorine “F2”, yielding almost unique types of bonding with the other elements [1].
The strategic importance of Solid-state inorganic fluoride materials will be illustrated by some examples taken from various fields.:
- Use of fluoride materials as electrodes in Li-ion batteries and in catalysis;
- Nanocrystalline metal fluorides derived from fluorite- (CaF2) or tysonite- (LaF3) types with high F--anionic conductivity and used as solid electrolytes in F- ion-based all-solid-state batteries.
- Fluorides in photonics: luminescence, up- and down-conversion, frequency-doubling fluorides and solid-state lasers ;
- Multiferroics based on d-transition metal fluorides derived from the perovskite, i.e. layered BaMF4 or TTB-K3Fe5F15, in which magnetism and ferroelectricity coexist.
- F-doped SnO2 for photo-voltaic applications exhibiting a rather good transparency in the visible range and high infrared absorption associated to its conductivity due to n-type charge carriers
-Perovskite-related solid-state fluorides based on d-transition metals exhibit a huge variety of structural and magnetic behaviors. Layered BaMF4 and iron fluorides (TTB- K3Fe5F15), are important families of multiferroics,
-Intercalated fluoride ion in several networks of oxides allowing to tune the transition metal oxidation state. F-based superconductors created by F-doping in cuprate systems La2CuO4 and Sr2CuO3 or in F-doped oxypnictide LnFePnO1-xFx (Tc ~58 K)
- Finally, nanoparticles of solid-state inorganic fluorides are used in many advanced domains such as dye-sensitized solar cell (DSSC), transparent conducting films (TCF), solid state lasers, nonlinear optics (NLO), up- and down-conversion luminescence, UV absorbers, frequency doubling. Their role is decisive in medicine and biotechnologies, where nano-crystals of doped rare-earth fluorides can be used as theranostic nano-agents that integrate imaging probes and therapeutic and are therefore able to perform both therapy and diagnostic within a single nano-object.

Electrical resistance is a well-known natural phenomenon that allows such interesting applications as electrical heating, through the Joule effect, caused by the collisions of electrons with the crystal lattice. In any case, it is clear that the existence of materials without electrical resistance would be extremely interesting and, among other applications, would allow the transmission of electrical energy without losses, which would mean savings of the order of between 2 and 12% of the cost of total electricity transmission in the whole world.
However, apart from the economic aspect just mentioned, electrical conductivity without resistance, called superconductivity, has, in addition to great scientific interest, a good number of applications, such as obtaining NMR images, and constitutes one of the most attractive and interesting fields of study in Materials Science, Physics and Chemistry.
A significant difficulty, is however, the need to use low temperatures to reach the superconducting state, discovered in mercury at the beginning of the 20th century, below a temperature of around 4 K.
In the present lecture, which aims to present a simple overview of the subject, fter going through a long succession of discoveries and improvements in which critical temperatures were reached of up to 138 K in such varied and diverse materials, as metallic elements, alloys, pnictides and cuprates, it will be shown that, at the present time, it is the hydrides that occupy the scene. Indeed, even if the materials obtained so far require the use of quite high pressures to achieve the superconducting state, in those cases this taks place at much higher critical temperatures, around room temperature . Thus, it has been possible to reach 203 K in a "sulfur hydride: H2S" at a pressure of 150 GPa and, shortly after, 288 K was reached in the lanthanum hydride LaH10, but at still higher pressures, of the order of 300 GPa and beyond.
This talk will then describe, in moderate detail, the phenomenon of superconductivity; then after exploring recent work in the very interesting case of hydrogen itself and on hydrides, including the most common hydrogen sulfide and oxide, SH2 and H2O respectively and their, somewhat unexpectedly, non-negligible possibilities of superconducting, we will end with the latest news on the remaining, and very promising, superconducting metal hydrides.

Carbon-based chemical compounds and materials are relatively inexpensive and very effective as selective Electron Transporting Layers (ETLs) in solar cells. Our work in this area has been primarily with buckminsterfullerene compounds, also called “buckyballs” or simply fullerenes, which are pure-carbon cages that are excellent electron acceptors and 3D transporters. We have functionalized fullerenes in order to modulate and probe their specific interfacial interactions in perovskite solar cells to understand the details and to enhance the cell performance efficiencies. Pyridine-functionalized fullerenes were tested as ETLs, both as pure compounds as well as in combination with other ETL compounds in order to discriminate their ability to extract electrons at the perovskite interface and to transport the electrons through the bulk phase. Results clearly showed that the pyridine-functionalized compounds act as efficient electron extractors at the interface but are not good electron transporters as a bulk phase.
In addition to regular fullerenes we have also worked with endohedral versions, which are carbon cages which encapsulate ions and/or atoms and clusters inside, stabilized by electronic interactions with the cages. These nano-sized compounds, which we also call “Buckyball Maracas” due to their composition and structure, were recently shown to act as reasonably efficient non-precious metal-containing molecular catalysts to effect the Hydrogen Evolution Reaction (HER), or water splitting, to produce hydrogen gas. We initiated this work and are currently exploring the fundamental aspects of the HER with other endohedral fullerene compounds, both to understand the details and to increase their efficiencies.

The main objective of this work was to analyze and understand the geological and tectonic constitution of the municipality of Algodão de Jandaíra, state of Paraíba and offer a contribution to mineral research, whether local or regional, since the municipality is inserted in the Borborema Province in northeastern Brazil, rich in industrial and metallic minerals such as tantalite/columbite, gold, scheelite, gemological minerals (beryl, marine water, tourmalines), etc. The geochemical parameters were defined using the portable X-ray fluorescence analytical instrument (p-XFR) for some major elements, traces and light rare earth (ETR-L) elements in active stream sediments, basalt vein, in pegmatite dike and quartz veins, in order to enrich the scientific literature regarding the advancement of research on mineral potential in any regions of Borborema Province. The results obtained by p-XFR, when plotted in tables and graphs, contributed to the important interpretations on ore content, geochemical associations, magmatic evolution and contribution of hydrothermalism, geological and tectonic weathering in the geochemical mobilization of the elements. Field research shows that the tectonic modeling of the rocky bodies of the studied area has a strong local structural control exercised by the Pocinhos and Casserengue shear zones. The set was the target of strong compression, stretching, boudinagem and injection of veins. Tectonic reactivations of extensional character were responsible for the production of open fractures, orthogonal to the regional trend, allowing the intrusion of basalt veins, modeling the drainage pattern and generating vertical walls that served as a panel for rock art, with prehistoric paintings made by ancestors, such as the pedra da letra in the passagem river. The studies culminated in the preparation of the Course Completion Work.

Materials under ultrahigh pressure (HP) exhibit a variety of interesting properties.[1] However, some of the HP-phase materials that are thermodynamically stable under HP (> 10 GPa) transforms into amorphous or different crystalline phase during decompression. If this back-transformation can be suppressed, we can obtain some functional HP-phase materials to be utilized in the future. To obtain such HP-phase materials under ambient pressure, we focused on the epitaxial stabilization of metastable-phase materials and came up with the idea of applying HP to thin-film samples.[2]
We first investigated an HP-phase, α-PbO₂-type TiO₂ (orthorhombic, a = 0.454 nm, b = 0.549 nm, c = 0.491 nm). This phase is obtainable under ambient pressure. Unfortunately, most of the reported data was about the product in the form of powder, and only a few reports about the fabrication of single crystals are currently available. In particular, single-phase epitaxial thin films have not been reported. In this study, we developed a technique for applying HP (8 GPa) to thin-film samples. Using a rutile TiO₂(100) epitaxial thin film as a precursor, we fabricated epitaxial thin films of single-phase α-PbO₂-type TiO₂(100) by inducing a structural phase transition at ultrahigh pressure.
Thin films of epitaxial rutile TiO₂(100) (thickness: ~100 nm) were deposited as precursors on Al₂O₃(001) (5 mm in diameter and 0.5 mm in height) using pulsed laser deposition. HP treatment for thin films was performed using a Kawai-type multi-anvil HP apparatus. The precursor thin film was heated up to 1000 °C under HP of 8 GPa, and then kept for 0.5 h. After the heating step, the film was quenched to room temperature (RT), followed by decompression.
The results of X-ray diffraction and Raman spectroscopy indicate that a single-phase α-PbO₂-type TiO₂(100) epitaxial thin film has been obtained. It should be stressed here that rocking-curve full width at half maximum of the 200 peak showed a quite small value of 0.11°, indicating very high crystallinity. Our present study indicates that HP treatment to thin-film samples allows us to fabricate high-quality HP-phase epitaxial thin films.

Dealloying, or chemically etching a material to selectively remove one or more less- noble components from the base metal, appears as an attractive process to generate metal networks for unique materials, which are in demand with modern technologies in biochemistry and medicine, catalysis, electrochemical energetics, etc. [1];[2]. Progress in this area were recently been described in Ref. [3].
The effect of duration time and composition on the microstructure and morphology of ultraporous iron was studied by electrochemical dealloying (selective anodic dissolution) of iron-manganese alloys (Mn wt% = 33; 67) in a molten equimolar mixture of NaCl-KCl and NaCl-KCl-CsCl eutectic. The possibility of electrochemical fabrication of ultraporous iron in the percolation mode at the temperature above the recrystallization annealing of steel was shown. Voltammograms (CV) were measured, and the range of potentials for the selective manganese dissolution in the specified equimolar mixture at a temperature of 700-750 ° C was found. The exposure time at a potential of 0.1 V is about an hour for the formation of a characteristic bi-continuous percolation structure of pores and ligaments. It was found that, during dealloying of ferromanganese with a Mn content of 33 wt%, manganese was etched out almost completely, and the ultraporous iron has much more uniform pore and ligament size.
Acknowledgments: The reported study was funded by RFBR, project number 20-33-90224

In spite of free-atom electronic-relaxation contributions to transition-metal cohesive-energies (E_coh), numerous studies have misused the latter instead of using genuine interatomic bond-energies (E_b) in modeling bulk and surface properties [1-2], including atomistic-potential parametrization for nanoalloys. The required E_coh modification consists of s to d electronic promotion energy plus the magnetic spin-polarization energy (in accordance with Hund’s first rule). The latter was computed [3] for the 3d, 4d and 5d series using the local spin-density approximation (LSDA), whereas the former was obtained from spectroscopic data.
This work first reveals that eliminating these free-atom contributions from experimental cohesive-energies leads to highly accurate linear correlations of the resultant bond-energies with melting temperatures and enthalpies, as well as with inverse thermal-expansion coefficients, specifically for the fcc transition-metals. In addition, predictions of surface segregation phenomena in Cu-Pd and Au-Pd bulk alloys on the basis of the correct energetics are in much better agreement with reported LEISS experimental results. A distinctive demonstration of the problem and its solution involves the significant impact of the cohesive-energy modification on segregation (separation) phase transitions in Cu-Ni truncated-octahedron nanoalloys. In particular, without the correction destabilization of Janus configuration in favor of core-shell is erroneously obtained. Preliminary computations for Cu-Ni-Pd ternary nanoalloys reveal significant effects of Pd and of the fixed energetics on chemical-order and transition temperatures.
Generally, the introduced correction procedure should be applicable also to other bond-energy related properties of any transition metals, alloys as well as nanoalloys.

Transition metal oxides often having a perovskite structure form a wide and technologically important class of compounds. In these systems, ferroelectric, ferromagnetic, ferroelastic, or even orbital and charge orderings can develop and eventually coexist. These orderings can be tuned by external electric, magnetic, or stress field, and the cross-couplings between them enable important multifunctional properties, such as piezoelectricity, magneto-electricity, or magneto-elasticity. Here, will illustrate with different examples of utilization of oxide films. First, by growing PrVO3 thin films epitaxially on an SrTiO3 substrate, I will show that the role of oxygen vacancies can be rationalized to introduce a chemical strain similar to the so-called mechanical strain (±2%), which in turns produce a nontrivial evolution of Néel temperature in a range of 30 K. I will also present the effect of thickness, and other substrates. Second, I will show that they can also be used as bio-adaptive surfaces, a field of research which is clearly unexplored. For this, we prepared a series of oxide thin films by the pulsed laser deposition technique, grown mesenchymal stem cells on these surfaces, and studied their adhesion and proliferation. We will discuss the feasibility of different thin films to promote appearance of multicellular structures with a better performance in terms of cell proliferation. These results will confirm the potential of such materials for various applications in electronic or medicine.

Modern high pressure chemistry represents a vast exciting area of research which will lead to new industrially important materials. Compared to traditional solid-state chemistry, this field is only just beginning to realize its huge potential and the image of “terra incognita” is not misused. Nowadays high pressure chemistry takes advantage of advances in X-ray diffraction. Actually, research over the last ten years has seen intensive use of in situ synchrotron radiation for direct observation of both stable and metastable synthesis pathways under extreme conditions. This strategy removes the limitations of the old ex situ ‘cook and look’ procedure. The possibility of observing synthesis in situ permits much greater precision in establishing the thermodynamic conditions needed for accessing metastable states. In this talk, I will show that the use of very high pressures and temperatures combined with the in situ probe by X-ray diffraction with synchrotron radiation is the methodological key to control the composition and microstructure (nanostructuration) of new bulk light materials (borides, carbides, Si compounds, etc.) with outstanding properties and I will give many examples from our recent studies [1-5].

References:
[1] Y. Le Godec*, A. Courac, V. Solozhenko. High-pressure synthesis of superhard and ultrahard materials. Journal of Applied Physics, American Institute of Physics, 2019, 126 (15), pp.151102.
[2] S. Pandolfi, C. Renero-Lecuna, Y. Le Godec* et al. Nature of Hexagonal Silicon Forming via High-Pressure Synthesis: Nanostructured Hexagonal 4H Polytype. Nano Letters, American Chemical Society, 2018, 18 (9), pp.5989 - 5995.
[3] R. Grosjean, Y. Le Godec*, S. Delacroix et al.. High pressures pathway toward boron−based nanostructured solids. Dalton Transactions, Royal Society of Chemistry, 2018, 47 (23), pp.7634−7639.
[4] Y. Le Godec*, M. Mezouar, D. Andrault, V. Solozhenko, O. O. Kurakevych, BORON CARBIDE AND METHOD FOR MAKING SAME, European patent 08787929.2.
[5] Y. Le Godec*, V. Solozhenko, O. O. Kurakevych, N. Dubrovinskaia, L. Dubrovinski, NANOSCALE BORON NITRIDE, US patent USPTO 20110230122.

In this work we utilise luminescent properties of Mn⁴⁺ doped Li₄Ti₅O₁₂ - a very promising material for ultrafast-charge-discharge and long-cycle-life batteries [1]. Applying lifetime-based luminescence thermometry on Mn⁴⁺ doped materials the remote and non-contact temperature readings are possible with great relative sensitivity [2-4].
The Mn⁴⁺ doped Li₄Ti₅O₁₂ samples were prepared by the one step solid-state method using stoichiometric amounts of Li₂CO₃, TiO₂ and MnO₂ at 850 ^oC to obtain cubic spinel structure with space group Fd-3m as confirmed by X-ray diffraction analysis. In this host, Mn⁴⁺ is in a strong crystal field providing the strong absorption around 500 nm due to ⁴A_2g →⁴T_2g electric spin-allowed electron transition and with emission around 679 nm on account of ²E_g →⁴A_2g spin forbidden electron transition. Due to the coupling to phonon modes of the host material [5] the change of radiative decay rate (radiative lifetime) starts at very low temperatures (»75 K). In addition, the low value of energy of ⁴T_2g level (20000 cm−1) leads to the strong emission and radiative lifetime quenching starting at low temperatures (»250 K) which favours the use of this material for the luminescence thermometry in a broad temperature range.
Temperature dependences of photo-luminescent emission spectra and emission decay are measured over the 10–350 K range exhibiting quite large value of relative sensitivity (2.6% K−1@330 K) that facilitates temperature measurements with temperature resolution better than 0.15 K around room temperature.

Summary γ-Al-2O3:Sm²⁺ coatings were synthesized by the plasma electrolytic oxidation (PEO). The emissions originate from 4f⁵5d¹→4f⁶ and 4f⁶→4f⁶ transitions of Sm²⁺. The emission spectra, recorded from 300 K to 673 K, reveled the rapid diminution of the ⁵D₀→⁷F_J transitions with increasing temperature. The 5d→4f broad-band emission increases in intensity up to 225 °C. The high-luminescence intensities and opposite intensity vs temperature trends of these emissions are an indication of the high sensitivities and low temperature resolution. The luminescence intensity ratio (LIR) are well-fitted to the Boltzmann distribution and the energy-crossover model with relative sensitivities: 3.5 %K-1 @ 300 K and 1.5 %K-1 @ 540 K. Introduction Sm2+ has a wide excitation band [1]. The emission spectrum of Sm²⁺ features a broad-band due to 5d-4f transition and a series of sharp peaks due to 4f-4f transitions. The discovery of Al₂O₃:Sm²⁺ [1] provided an opportunity for the investigation of this material as temperature sensor. The indications of its high potential for the phosphor thermometry were the existence of both the 5d-4f and 4f-4f emissions, high emission intensities, wide choice of excitation wavelengths, and the sole importance of the substrate material itself. The significant overlap of 5d with ⁵D₀ level is an indication of the highly efficient f-f transitions [2]. The complete thermometric analysis was carried out. Methods 99.9% pure aluminium, 6061 and 7075 aluminium alloys were used as anode during the PEO. XRD was used for investigation of the coating crystallinity. High-stability 473 nm laser was used as an excitation source. The beams were transferred via a fiber-optic bundle. Emission spectra were recorded by the high-resolution spectrograph. The samples were placed on the liquid nitrogen cooled hot/cold stage. Results Emission spectra for LIR and LT were recorded from 100 K to 673 K. The ⁵D₀→⁷F_J emissions rapidly drop with increasing temperature, while the 4f-5d increases up to 225 °C. LIR is estimated from the ratio of 5d-4f and 4f-4f transitions, giving the excellent relative sensitivity values. Luminescence lifetime of ⁵D₀→⁷F₀ is fitted to the energy crossover model [3], with maximum relative sensitivity 1.5 %K-1 @ 540 K. Conclusions A steady-state and time-resolved thermometry on a wide temperature range was carried out on the highly luminescent phosphor incorporated in the coatings of possibly the most important industrial material. LIR following Boltzmann distribution showed sensitivity among the highest ever recorded. The lifetime rapidly drops with increasing temperature.

There are a number of commercially available lasers with different emission parameters. Among these, wavelength, continuous or pulse emission, pulse repetition rate and nominal power are essential. The laser emission can further be modified by the optical systems employed to modulate the output beam.
The above laser emission parameters enable controlled irradiation of solids to induce significant chemical and physical modifications of their surfaces in any type of environment and with ease of scalability to large areas.
Several distinct types of interactions may be described for laser irradiation of solids, with underlying photothermal, photophysical and photochemical mechanisms. The most commonly applied in industry are based on photothermal transformations, where melting is induced on solid surfaces for welding and conventional cutting operations. Appropriate beam steering enables focusing geometries which allow directional solidification of solids from their melt in circular and planar fashion. In contrast, short pulse laser irradiation of solids may induce ablation phenomena, whereby material is selectively removed from the irradiated area, generating new surface properties.
The above processes will be examined in this talk, using examples derived from the preparation of textured and nanostructured functional solid surfaces.
Acknowledgements. Work funded by EU project SPRINT (H2020-FETOPEN 801464) the Spanish MCIN/AEI/10.13039/501100011033 (project PID2020-113034RB-I00) and by Gobierno de Aragón (research group T54_20R).

Temperature plays an essential role in biological systems, affecting a variety of their properties. For example, the cell division rate, and consequently tissue growth, are both critically influenced by temperature. The precise measurement of temperature is needed for both early diagnosis and treatment of malignant diseases. Nowadays, luminescence thermometry is considered to be a promising tool for non-invasive bio-thermal-imaging [1]. For such use, the biocompatible and near-infrared-emitting nanoparticles showing the strong temperature dependence of emission are urgently needed. Working within a near-infrared spectral region (the first and second biological windows) overcomes small light penetration lengths occurring with visible-emitting nanoparticles since in biological windows the extinction coefficient of tissues is low due to a simultaneous reduction in both tissue scattering and absorption coefficients [2]. Herein, well-known Yb3+,Er3+-doped yttrium aluminium garnet (YAG) nanopowder is prepared by the combustion method. The cubic structure of the material was confirmed by X-ray diffraction measurements, while UV-Vis-NIR diffuse reflectance showed typical Yb3+/Er3+ absorption bands. We have investigated the temperature dependence of near-infrared emission of the phosphor aiming to compare the thermometric performances of two different read-outs: i) changes in the intensities of emission bands and ii) changes in the emission bands position and bandwidths. Temperature dependant near-infrared emission spectra were measured in the 1000-1550 nm spectral range upon 980 nm excitation. Following combinations were investigated: i) luminescence intensity ratio of 1470/1530 nm Er3+ emission lines; ii) luminescence intensity ratio of 1030 nm Yb3+ and two Er3+ emission lines (1470 and 1530 nm); iii) Yb3+ emission band position and iv) Yb3+ emission bandwidth (FWHM). Among investigated read-out approaches, the most important figures of merit, absolute and relative sensitivities, and temperature resolutions have been calculated and compared.

Carbon nanotubes and graphene are almost perfect molecules with truly amazing combinations of thermal, electrical and structural properties. In order to achieve their full potential they need to be fully integrated hybrid materials in all sorts of matrices. Full integration requires their development beyond conventional composites so that the level of the non-nano material is designed to integrate fully with the amount of nanotubes and graphene. Here the nano materials are part of the matrix rather than a differing component, as in the case of conventional composites. In order to advance the development of multifunctional materials integrating nanotubes and graphene, this research is focused on the simultaneous control of the nano architecture, structural properties, thermal and electrical conductivity of fully integrated hybrid materials. These hybrid materials systems are designed to surpass the limits of rule of mixtures in conventional composite design. The goals are to implement multifunctional designs to fully mimic the properties of carbon nanotubes and grapheme on larger scales for enhanced thermal and electrical management in addition to the control of other properties such as strength, toughness energy and power. These new approaches involve exfoliation, functionalization, dispersion, stabilization, alignment, polymerization, reaction bonding and coating in order to achieve full integration. Typical examples of structural applications of polymeric and ceramic matrices and applications in energy systems such as capacitors and batteries as well as other material systems are presented and discussed.

The abundance of sodium and the physical-chemical similarities with lithium make sodium batteries a technology to the Lithium ones, with the potential to produce disruptive changes in the transition towards cleaner and sustainable energy sources less dependent on fossil fuels. In this experimental work, we propose a new processing methodology, based on the combination of tape-casting and hot-pressing, to develop high performances ceramic NASICON electrolytes with formula Na3.16Zr1.84Y0.16Si2PO12 and high ionic conductivity (from 0.12 mS/cm at 20ºC to 1.29 mS/cm at 100ºC), wide electrochemical window (from 1.5V to 4V), good mechanical properties and (325 HV of hardness) and high thermal stability. In order to study the compatibility of the chemical and electrochemical characteristics the electrolytes with the solid-state battery approach, half-cells (Na0/NASICON/FePO4) were prepared and tested at room temperature. Preliminary results reveal that capacity slightly increases as the number of cycle does, reporting values of up to 85 mAh/g (at a C-rate of C/20), about 50% of the theoretical capacity and 60% of the capacity typically reported for their liquid-based counterparts. Due to these results were obtained for room temperature, the application scope of the proposed electrolytes broadens not only to stationary applications but to transport, where highly efficient and sustainable devices are highly demanded. Therefore, the all-solid-state sodium battery based on Na0/NASICON/FePO4 here proposed demonstrates to be functional and a potential competitor for current all-solid-state batteries based on the electrochemistry of lithium.

Interest in materials exhibiting oxygen ion and/or proton conduction has increased during the last years owing to their great importance for energy and environmental applications.
Ceria-based oxides are regarded as key oxide materials because rare earth-doped ceria shows a high oxygen ion conductivity even at intermediate temperatures. Using density-functional theory (DFT), we have investigated defect interaction and oxygen migration energies as well. By means of Kinetic Monte Carlo (KMC) simulations we then investigated the oxygen ion conductivity. We show that all interactions between the defects, namely vacancy-dopant attraction, dopant-dopant repulsion and vacancy-vacancy repulsion as well contribute to the so-called conductivity maximum of the ionic conductivity [1].
BaZrO₃-based oxides are proto-type proton conductors. Using density-functional theory (DFT), we have investigated defect interaction and proton migration energies in Y-doped BaZrO₃. The macroscopic proton conductivity was then investigated by means of KMC simulations. We discuss the resulting proton conductivities concerning special percolation pathways for protons [2].
Finally, we compare our theoretical results with experimental ones and discuss similarities and differences between oxygen ion and proton conductors.

We study the potential of material simulations based on first-principles methods to predict gas sensing properties of 2D materials. This emerging class of materials is of particular interest to gas sensing applications due to high surface-to-volume ratios and chemical stability. We discuss in detail results of electron transport calculations within the Landauer-Büttiker formalism and compare the conclusions to analyses in terms of adsorption energies‚ charge transfers‚ and work functions. Specific examples include the effects of the interlayer interaction in bilayer MoS2 and WS2 on the gas sensing performance and the consequence of the presence of reactive Si in Si2BN. We also address the properties of C3N and para/meta-C3Si. Potential of very sensitive gas sensing is demonstrated for para-C3Si and is explained by the susceptibility of Dirac states to symmetry breaking distortions rather than by a mechanism based on charge transfer. Finally‚ the enhanced gas sensing performance of monovacant C6BN is studied and it is shown that the work function changes of both pristine and monovacant C6BN during gas adsorption do not correlate with the changes observed in the I-V characteristics.

In order to achieve a sustainable human presence on the Moon, Mars, and beyond, humanity must develop the capability to provide as close to 100% supply of resources in-situ as possible. Achieving this goal will require development of technologies to locate, extract, process, generate, and utilize said resources. To date, contemporary in-situ resource utilization-based space exploration architectures typically focus on the production of resources that have the most value for initial use in space such as O₂, H₂, and H₂O for the production of propellant and life support consumables [1]. However, critical metals indispensable to the terrestrial global economy such as Ni, Cu, Co, and the platinum-group elements will also likely be required to support the endeavor of becoming a multi-planetary species [2,3], and on this topic Mars becomes the focus. Based off compositional and petrographic similarities between terrestrial mantle-derived mafic/ultramafic magmas, meteorites known to come from Mars, and the physicochemical characteristics of the Martian surface, it is likely that massive and disseminated sulfide ores, which host these precious resources, were deposited at or near the surface [4,5]. In order to validate this belief, a more thorough exploration campaign is required to properly assess whether Mars is an ore-rich planet. Thus, this paper will provide an overview on the current state of knowledge and technologies available for prospecting for magmatic sulfide ores on Mars, with a particular focus on the capacity and necessity of integrating sustainable practices in upcoming space missions focused on in-situ resource utilization. Additionally, potential use cases of metals derived from magmatic sulfide ores in the space industry are considered.

The field of Solid State Ionics is concerned with the understanding and tailoring of defects, diffusion and reactions in solids. It has nowadays wide technological applications in energy conversion and storage, data storage, sensors etc. Thus, Solid State Ionics and its technological implications are inevitable for a future sustainable development of our world.
In this contribution I will, however, focus on some fundamental questions and still unresolved problems in the Science of Solid State Ionics. For this purpose, I will start with a brief history of Solid State Ionics showing the foundations of the field. Then I will focus on two major topics: The first is concerned with the role of defect interactions. This topic is of particular importance in materials with high defect concentrations where defect interactions are unavoidable. Interestingly, nearly all materials with technological importance belong to this class of materials. In contrast, the theoretical treatment of interactions is mostly limited to diluted systems. I will show a possible route to solve this problem by combining ab initio calculations with Monte Carlo simulations [1]. In this way, not only the problem of defect interactions can be solved, but also the link between the microscopic energetics and dynamics and the macroscopic thermodynamics and kinetics can be made. As examples, I will discuss our results for oxygen ion conductors and proton conductors [2,3].
The second topic is concerned with the number of components in a material. Nowadays, most materials in Solid State Ionics are multicomponent materials containing, e.g., three or more chemical elements. Thermodynamically, this is a challenge as the phase diagrams become rather complicated and are mostly unknown. On the other hand, there is another subtle problem which is concerned with the number of mobile species. Historically, in solid state kinetics only two mobile species were considered, e.g., two mobile cations during interdiffusion or one mobile anion and electrons in mixed conductors. The situation becomes, however, more complicated if there are three mobile species, e.g., two ionic defects and one electronic defect. I will discuss corresponding examples and the thermodynamic and kinetic implications [4,5].

Covalent organic frameworks (COFs) are an exciting family of functional porous materials. They feature uniform yet tunable porosity, rich chemical composition, and potentially high stability suitable for various applications. However, their structural dynamics are less explored than other porous materials, and their growth mechanism remains unclear. In this talk, I will introduce our group's recent progress in studying the structural dynamics and growth mechanism of several COFs. The results provide new approaches to design, synthesis, and applications of new functional COF materials and devices.

Zirconia based materials have a variety of unique physicochemical, electrical and mechanical properties including high strength, hardness, impact toughness, wear resistance, low coefficient of friction, high melting point, chemical inertness, low heat conductivity and biocompatibility. These properties account for the wide range of applications, from wear resistant bearings to medical and surgical instruments. As a rule, the mechanical properties of these materials depend on the composition, namely, on the type and concentration of stabilizing and doping oxides, which are introduced in small concentrations to improve the functional characteristics of the material and to ensure the stability of these characteristics under operating conditions [1-4].
The aim of this work is to study the effect of a number of dopants on the structure and mechanical properties of 2.5Y0.5RSZ crystals (where R is Ce, Nd, Er, Yb) depending on the ionic radius of the impurity cation. Partially stabilized zirconia (PSZ) crystals were grown by directional melt crystallization in a cold crucible at a 10 mm/h crystallization rate.
The phase composition and crystal structure of the material was studied using X-ray diffraction, Raman spectroscopy and transmission electron microscopy. The studies showed that the PSZ crystals have two tetragonal phases (t and t’) with different tetragonal distortion degrees. TEM studies showed that the crystals of all compositions are a complex twinned domain structure, which is formed during the transformation from the cubic to the tetragonal phase during the cooling of the crystal.
Mechanical characteristics were measured by Vickers indentation technique. The microhardness and fracture toughness for different crystallographic planes have been tested by indentation with different indenter diagonal orientations. Depending on the composition and orientation of the sample, the values of fracture toughness varied from 10 to 15 MPa∙m^1/2.
The work was supported by research grants № 18-13-00397 of the Russian Science Foundation.

In this work, one step solid state method was used to obtain Li₄Ti_5-xMn_xO₁₂ (x = 0 - 0.08) powders starting from oxide precursors sintered at 850°C. Tetravalent manganese ion was taken as an optical activator and incorporated in lithium titanate (LTO) material. The material can potentially be used in various applications, such as white light emitting diodes, biolabeling, thermoluminescence, etc. Manganese(IV) efficient red luminescence can be color converter of warm white LEDs, composed of a blue emitting diode combined with a green-yellow emitting phosphors, and in such way improve colour-rendering index. Also, it can be used for thermoluminescence contactless measurements. [1]
Being a transition metal with 3d3 electronic configuration Mn(IV) is subject to a significant impact of host lattice. XRD measurements confirmed that the LTO samples crystallise in cubic spinel structure with Fd-3m space group. Three out of four Li ions (in the molecular formula Li₄Ti₅O₁₂) are situated at the tetrahedral 8a site, while the forth Li and Ti(IV) ions randomly occupy the octahedral 16d site with a ratio of 1:5, respectively. Point symmetry of Ti(IV)/Mn(IV) site is -3m (D3d).
Kubelka-Munk function, based on measured diffuse reflectance spectra, showed gradual decrease od band gap energy with Mn(IV) concentration increase in the set of synthesized materials. Reflection and excitation spectra showed that samples can be efficiently excited by λ=500 nm. Emission peaks of Mn(IV) centered at 681 and 696 nm originate from spin-forbidden ²E_g → ⁴A_2g electron transitions. Lifetime of the transition was determined in 0.136-0.200 ms range.
The sample with the highest Mn(IV) emission intensity was co-doped with different concentrations of Nb(V), used as a sensitizer to improve luminescent properties. [2] It was observed that the intensity was increased up to 10%.

Iron-based unconventional superconductors with quasi-two-dimensional crystal structure have attracted intense interest after the critical temperature of FeSe was enhanced by more than one order of magnitude in the thin layer deposited on top of an insulating oxide substrate. In heterostructures comprising interfaces of FeSe with topological insulators, additional interesting physical phenomena are predicted to arise e.g. in the form of topological superconductivity [1].
Importantly, the tetragonal FeSe phase relevant for superconductivity is stabilized by excess Fe, leading to non-stoichiometric Fe(1+δ)Se compounds [2]. However, the number of first-principles computational studies considering excess Fe is limited. We have studied Fe(1+δ)Se employing the coherent potential approximation and the tight-binding linear muffin-tin orbital method, which are well suited for disordered systems and can treat systems with even a very small off-stoichiometry without the need for a large supercell. It also allows us to explicitly address the impact of chalcogen vacancies.
Furthermore, we have examined the effect of chalcogen height for both FeSe and Fe(1+δ)Se. This parameter has been determined with only a limited accuracy so far, and it appears to affect the band structure significantly here. At an interface such geometrical properties can be strongly modified, as compared to the bulk case. Calculated band structures are compared to experimental ARPES data [3].

The huge experimental material presented in the world scientific literature confirms the correctness of M. Faraday's views on the effect of electric current on chemical reactions. The key points in the development of scientific ideas on the nature and the mechanism of physicochemical processes are the following provisions of the works of M. Faraday: the identity of energy manifestations in the interaction of material objects and the discrete nature of the electric current. Theories developed without taking into account the works of M. Faraday made it possible to disregard the identity of energy manifestations in the interaction of material objects. This circumstance also influenced the lack of attention to the use of the discreteness of the electric current for practical application. We have shown that a change in a wide range of electrical signal parameters can promote unusual chemical reactions and physicochemical processes at the interface and in condensed systems. For example, we found that under the influence of electromagnetic fields, the electrical conductivity of melts can decrease with increasing temperature and change at a constant temperature. Crossed electromagnetic fields cause phase and quantitative division of melts, both synthetic oxide melts and oxide-sulfide multicomponent systems, etc. etc. We need specific knowledge about production objects: solid, gaseous and liquid. If with the first two objects the situation is more or less acceptable, then modern science knows surprisingly little about the liquid. The discussion about the structure of liquid systems has not stopped for over a hundred years. The official scientific point of view on the nature of liquids was formed at the beginning of the 20th century, when the outstanding Swedish scientist Svante Arrhenius received the Nobel Prize in Chemistry in 1903. The prize was awarded to him "... for his services to the development of chemistry with his electrolytic theory of dissociation" (1903 to Professor S. Arrhenius, Stockholm, for the services he has rendered to the advancement of chemistry by his electrolytic theory of dissociation). His theory was supported by Nernst and Tubandt. This served as the basis for considering the Arrhenius theory as a scientific fact, and not as an assumption. Over time, this theory became the official scientific point of view, and was called the "theory of electrolytic dissociation." Undoubtedly, the theory of S. Arrhenius, an outstanding scientist-chemist, had a significant impact on the development of technologies using the electrolysis process. The success of this theory for use in creating technologies in metallurgy was due to the availability of high quality raw materials. With the deterioration of the mineral resource base, the struggle of scientific ideas around the question of liquid has grown for metallurgists from a scientific field to a purely practical one. Fundamental concepts existing in world science have long ceased to satisfy practice. Changing theoretical concepts will cause a stream of non-standard technical solutions. Our experimental data can serve as a basis for creating effective technological processes. Some examples are presented below.
1. If we approach the problem of the structure of aluminate solutions, the presence of undissociated molecules in the solution made it possible to propose a method for the decomposition of aluminate solutions by the method of reversal of molecular dipoles "along the field" with the subsequent destruction of intermolecular bonds and destruction of molecular complexes.
2. Similarly, the use of the physical parameters of the electric current for the directed orientation of molecular complexes in melts makes it possible to propose a number of methods for reducing the loss of metals in the course of pyrometallurgical processes.
3. The use of the properties of the molecular nature of the structure of oils, in particular the presence of triboelectric effects at the interface of molecular structures, makes it possible to create technologies for corrosion protection of pipelines and equipment in the oil refining industry.
4. Taking into account Faraday's thesis on the identity of energy manifestations in the interaction of material objects made it possible to use the frequency-amplitude characteristics of plastic deformation and destruction of materials and structures to create technical solutions for the physical and mechanical strengthening of metal products.

Silicate-based inorganic phosphors have practical applications in many fields and their luminescent properties have been studied extensively. Among them, forsterite (Mg2SiO4) shows good chemical and physical stability, low dielectric permittivity, low thermal expansion and very good insulation properties. So, Mg2SiO4 finds practical application in different optical devices, tunable lasers, pigments, biomaterials and in electronics [1]. Furthermore, red emission of Cr3+ doped phosphors is commonly used in optical spectroscopy, in-vivo imaging, energy efficiency and luminescence [2,3]. The majority of standard thermometry methods tend to fail under room temperature. Therefore, novel temperature measurement principles are required for this temperature range. In this study, we aimed to explore the potential of Cr3+-doped Mg2SiO4 thermographic phosphor for cryogenic luminescence thermometry and thermometry in physiologically relevant window. Herein, the triple temperature read-out luminescence thermometry at cryogenic temperatures were tested using Cr3+-activated Mg2SiO4 near-infrared thermographic phosphor synthesized by combustion method. X-ray diffraction measurement confirmed orthorhombic crystal structure with the Pbnm (62) space group. Scanning electron microscopy revealed submicron size agglomerates composed of nanoparticles, and the presence of voids. In the forsterite Mg2SiO4 crystal, Cr3+ replaces Mg2+ at octahedral M1 and M2 sites with inversion (Ci) and mirror symmetry (Cs), respectively [4]. The octahedral M1 and M2 sites form the medium-field system resulting in the 2Eg → 4T2g narrow Cr3+ spin-forbidden emission at low temperatures. At higher temperatures (200–300 K), there are thermalization between 4T2g and 2Eg levels that leads to a broadband emission through 2Eg + 4T2g → 4A2g transitions [5]. The usability of this material for the luminescence thermometry was tested by three approaches: i) via temperature induced changes of emission intensity; ii) via temperature dependent luminescence lifetime and iii) via temperature induced changes of emission band position. Among investigated read-outs, the most important figures of merit, absolute and relative sensitivities, and temperature resolutions have been calculated and compared.

Topochemical reactions have led to great progress in the discovery of new metastable compounds with novel chemical and physical properties. The host lattice is considered to be generally immobile and rigid, and the overall crystal architecture of the host oxides is maintained. In my talk, I will present two cases where non-trivial structural conversions occur at low temperatures. The first example is the hexagonal nitride hydride, h-Ca3CrN3H, which converts to an orthorhombic nitride, o-Ca3CrN3, under hydrogen at 673 K, which is accompanied by a rotational structural transformation [1]. The second example is expressed by "Bi12O17Cl2 --> Bi12O17–0.5xFxCl2 (x ≤ 6)", where a sextuple Bi6O8.5 block with 1D rock-salt (RS) units in the FL matrix along the a-axis changes to alternate FL and RS slabs along the c-axis [2].

We have been working for some time on the synthesis at high pressure (P 12.5 < Gpa) and high temperature (T ≤1400 K) of new materials of the type MSr2RECu2O8 (RE <>Rare Earth), which formally derive from YBCO (i.e. CuBa2YCu2O7) by replacing the [Cu-O4] squares in the basal plane of the structure by [M-O6] octahedra (M <> Ru, Cr or Ir). The adequate formation of these cuprates as majority phases, can only be performed in a particular and relatively narrow window of P and T, outside which they cannot be obtained pure or even obtained at all¡. Yet, these “optimum conditions” bear a remarkable Gaussian correlation with the rare earth ion size, --the rare earth cation being at the centre of the unit cell in the YBCO setting--, and they do not follow the classic lanthanide contraction so often observed in the chemistry of those elements. Instead, interelectronic repulsion appears to play a major role in fixing the synthesis conditions. Moreover, the position of the Gaussian tip in the pressure-ionic radii space is also dependent on the transition metal that sits in the octahedron, in a way that seems related to the thermodynamic stability of their simpler oxides.
The second unusual example concerns the oxidation of Mo0.3Cu0.7Sr2ErCu2Oy, one of the superconducting perovskite derivative members of the above family (**). As shown by a detailed XPS study of its high oxygen pressure oxidation, the appearance of superconductivity is related to the oxidation of Molybdenum in parallel to the reduction of Copper.
The final example refers to an order/disorder process of a quadruple perovskite as function of High Pressure & High Temperature (***).
I thank my students for their contribution to this work.

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