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Information × Registration Number 0300U000929, 0198U001406 , R & D reports Title Investigation on electronic and crystal structure of high anisotropic oxides of the transitions metales with superconducting and segnetoelectric properties popup.stage_title Дослідження електронної та кристалічної структури високоанізотропних оксидів перехідних металів з надпровідниковими та сегнетоелектричними властивостями. Head Mel'nykov Volodymyr Stepanovych, Registration Date 18-10-2000 Organization nstitute of Geochemistry, Mineralogy and Ore Formation popup.description2 Structural research of hard solutions in system NdBa2Cu3O7-Nd2BaCu3O7+d (Nd123ss) showed, that exist three different types of structure. In interval 0<x<0,3 parameters of lattice Nd123ss linearly depend on Nd contents. The phase transition into tetragonal structure takes place attached to x=0,1. In interval 0,3<x<0,6 parameters a and c little depend on x ("plateau" on a, c(x)). At x=0,6-0,85 the second ortorombic phase is stable, which does not change symmetry by heating to 850-900°C. Temperature dependence of lattice parameters determines by interval х. Stoichiometric phase (x=0) shows approximately linear depending of a, c (T), but when x>0,25 crystalline structure of Nd123ss almost is insensitive to temperature. The compounds with x=0,1;0,15;0,2 reveals complicated dependence on temperature. The contents of oxygen in Nd123ss structure controls by x, but maximum value d does not exceed 0,30 - 0,35. Middle copper charge (v) is from 1,8 to 2, when x reaches 0,3, and further almost does not change (fo r x=0,8, v=2,05). The maximum critical temperature is equal 92К for x=0,05. The presence of super-stoichiometric oxygen in Nd123ss structure proves a possibility of his placing on vacant positions in Cu(1)plane, on axis а. Coordination of some Cu(1) atoms increases because the CuO5 or CuO6 polyhedrons are forming. The electronic structure of new-built R-blocks differs from R-blocks structure in stoichiometric phase. It be possible that thermal insensitive of Nd123ss with x>0,25 and ortorombic phase with x=0,7-0,8 can explain by presence Cu(1) with coordination more than 4. The crystal-chemical analysis of high-temperature superconductive with different "chemical" type R-blocks (Cu, Pb, Tl, Hg in positions of central cation), but with of the same type T-blocks [CuO2-A-CuO2] (A=Y, Ca) shows, that decisive sense for presence of superconductivity have type of central cation, his oxygenous coordination and distance cation-apical oxygen. Research of compounds AR2Pb2Cu3O8+d (R=Sr, Ba) showed, that accommodating in R-block of additional Pb - O layers rebuilds electronic structure of R-blocks. In result superconductivity exists Cu(1) when is found in twofold coordination and disappears when copper coordination increase. This effect quite opposed to that situation, which is observed in compounds of Y123 type. The CaBa2Cu3TlO7 and CaBa2Cu3HgO6 phases have the identical structures but different thallium and mercury coordination: 6 and 2 respectively. But they are superconductors with Tc 94 and 123К respectively. So change of oxygenous coordination central cation of R-blocks "dramatically" influences on Tc, but substituting for central cation on other with suitable coordination change takes care superconducting properties. Product Description popup.authors popup.nrat_date 2020-04-03 Close