| 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: 456/SolidStateChemistry/Regular (Oral) SCHEDULED: 14:50/Mon. 28 Nov. 2022/Andaman 1 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. (***) |
