Some Effects of Chemical Substitution and Applied Pressure on High Tc Copper Oxide Superconductors

Abstract

Recent experiments on the effect of Na and Pr substitutions and applied pressure on high Tc copper oxide superconductors are briefly reviewed. The Na and Pr substituted systems that were investigated include (La2-xNax)CuO4-δ, (Y1-xNax)Ba2Cu3O7-δ, and (Y1-xPrx)Ba2Cu3O7-δ, while the compounds studied under pressure were YBa2Cu3O7-δ and (Y0.5Pr0.5)Ba2Cu3O7-δ. The substitution of monovalent Na for trivalent La in La2CuO4-δ results in a continuous transition from semiconducting to metallic behavior, accompanied by the appearance of two superconducting components, one with Tc ≈ 20 K and the other with Tc ≈ 40 K, while the substitution of monovalent Na, and Pr, which appears to have a valence ~ +3.9, for trivalent Y in YBa2Cu3O7-δ produces a continuous transition from metal to semiconductor and a gradual suppression of superconductivity. The onset of Tc of YBa2Cu3O7-δ was found to increase from 95 K at 8 kbar to 107 K at 149 kbar, whereas applied pressure was observed to induce semiconducting behavior and suppress superconductivity in the compound (Y0.5Pr0.5)Ba2Cu3O7-δ.