Preparation and Properties of T' and T^* Phases in Ln₂CuO₄

Abstract

Substitutions of Ln were investigated on both Ln_1.85Ce_0.15CuO₄ (Ln=Pr, Nd, Sm, Eu) and La_0.85Ln'Sr_0.15CuO₄ (Ln'=La, Pr, Nd, Sm, Eu, Gd) in relation to pressure effect of Tc. The Tc values decreased with an increasing atomic number of Ln³⁺ in both T' phase of Ln_1.85Ce_0.15CuO₄ and T phase in La_0.85Ln'Sr_0.15CuO₄. The decrease in Tc agrees with the negative pressure effect of T' phase but conflicts with the positive pressure dependence of Tc in T phase. Oxygen amount, which is crucial for superconducting transition temperature Tc, changed as well as lattice parameter with the Ln substitution.