Charge compensation and optimal stoichiometry in superconducting (CaxLa1−x)(Ba1.75−xLa0.25+x)Cu3Oy

Abstract

The superconductive and magnetic properties of charge-compensated (CaxLa1−x)(Ba1.75−xLa0.25+x)Cu3Oy (normally denoted as CLBLCO) are considered through quantitative examination of data for electrical resistivity, magnetic susceptibility, transition width, muon-spin rotation, x-ray absorption, and crystal structure. A derivative of LaBa2Cu3Oy, cation doping of this unique tetragonal cuprate is constrained by compensating La substitution for Ba with Ca substitution for La, where for 0 ≤ x ≤ 0.5 local maxima in TC occur for y near 7.15. It is shown that optimum superconductivity occurs for 0.4 ≤ x ≤ 0.5, that the superconductivity and magnetism observed are nonsymbiotic phenomena, and that charge-compensated doping leaves the carrier density in the cuprate planes nearly invariant with x, implying that only a small fraction of superconducting condensate resides therein. Applying a model of electronic interactions between physically separated charges in adjacent layers, the mean in-plane spacing between interacting charges, ℓ=7.1206 Å, and the distance between interacting layers, ζ = 2.1297 Å, are determined for x = 0.45. The theoretical optimal TC0∝ℓ−1ζ−1 of 82.3 K is in excellent agreement with experiment (≈80.5 K), bringing the number of compounds for which TC0 is accurately predicted to 37 from six different superconductor families (overall accuracy of ±1.35 K).

Source-reported materials — not catalogue approval

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