Variation of Tc and resistivity in charge-compensated (CaxLa1-x)(Ba1.75-xLa0.25+x)Cu3Oy.

摘要: We report careful measurements of the transition temperature ${\mathit{T}}_{\mathit{c}}$ (${\mathrm{Ca}}_{\mathit{x}}$${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$) (${\mathrm{Ba}}_{1.75\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{La}}_{0.25+\mathit{x}}$)${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathit{y}}$ as a function oxygen content y, mainly for compositions x=0.1 and 0.4. This 1:2:3 superconductor family, that exists in composition range 0\ensuremath{\le}x\ensuremath{\le}\ensuremath{\sim}0.5, is tetragonal has maximal \ensuremath{\sim}82 K. Through mutual charge-compensating cosubstitutions, it preserves constant charge on noncopper cations (Q=7.25), independent x. observed monotonic decrease y varies from initial value \ensuremath{\sim}7.15 to insulator state roughly at y\ensuremath{\simeq}6.9. At metal-insulator (MI) transition, ${\mathit{y}}_{\mathrm{MI}}$ decreases with increasing Most unusual substantial increase by 21 24 K when x changes 0.1 0.4, under conditions where density remains constant. It accompanied twofold resistivity \ensuremath{\rho}. attribute this change band structure x, which occurs due Ca redistribution near La substitutes Ba. induces net electron transfer planes disordered chains. assumption supported lattice parameters implies mobile hole density, are responsible \ensuremath{\rho}, take place despite total being