2ND INTL SYMP ON SOLID STATE CHEMISTRY FOR APPLICATIONS AND SUSTAINABLE DEVELOPMENT

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.

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.

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].

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.

SIPS is the flagship event of FLOGEN STARS OUTREACH, a not-for-profit, non-political and all-inclusive science organization. SIPS as well as FLOGEN STARS OUTREACH takes no sides in political, scientific or technological debates. We equally welcome, without reservations, all spectrum of ideas, theories, technologies and related debates. Statements and opinions expressed are those of individuals and/or groups only and do not necessary reflect the opinions of FLOGEN, its sponsors or supporters.

FLOGEN Stars OUTREACH | Home | Contact Us | Privacy Policy | Cancellations/Refund Policy
© Copyright of FLOGEN Stars Outreach Organization: The content of this page including all texts and photos are copyright of FLOGEN Stars Outreach and none can be used in their original or in any modified or combined form in any publication, web site or in any other medium whatsoever without prior written permission from FLOGEN Stars Outreach.