ORALS

SESSION: SolidStateChemistryMonPM1-R6	Alario-Franco international Symposium (2nd Intl Symp on Solid State Chemistry for Applications & Sustainable Development)
Mon. 28 Nov. 2022 / Room: Andaman 1
Session Chairs: Udo Schwingenschlogl; Session Monitor: TBA

14:50: [SolidStateChemistryMonPM107] OS
When the High-Pressure Synthesis of HTSC Cuprates does not follow the Lanthanide Contraction…(but their properties do¡) and two more unusual reactions
Miguel Angel Alario Franco¹ ; ¹Universidad Complutense, MADRID, Spain;
Paper Id: 456 [Abstract]

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.

References:
(*) Inorganic Chemistry, Vol. 47, No. 14, 2008 6475. (**) Dalton Trans. 2015, 44, 10795. (***)

SESSION: SolidStateChemistryAM-Rpending	Alario-Franco international Symposium (2nd Intl Symp on Solid State Chemistry for Applications & Sustainable Development)
/ Room:
Session Chairs: TBA Session Monitor: TBA

: [SolidStateChemistryAM] OS
“Superconductivity: From Mercury to Hydrides: The Particular Case of Water"
Miguel Angel Alario Franco¹ ; ¹Universidad Complutense, MADRID, Spain;
Paper Id: 561 [Abstract]

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.

References:
Proceedings of the international symposium“Superconductivity and Pressure: A Fruitful Relationship on the Road to Room Temperature Superconductivity”. May, 21-22 - 2018. Madrid - Spain