Tetragonal High-Tc Superconductor in the System Ba2Y(Cu1-xGax)3O7-δ

Abstract
We synthesized single-phase compounds in the system Ba2Y(Cu1-x Ga x )3O7-δ (x = 0.02, 0.05 and 0.1). They are orthorhombic but the difference between their a- and b-axis dimensions rapidly decreases with increasing x. The compound at x = 0.1 is almost tetragonal (b/a = 1.001), whereas its c-dimension remains nearly the same as that of orthorhombic Ba2YCu3O7-δ. The oxygen content in the compounds increases according to 7-δ=6.92+0.43x. T c decreases as the Ga content increases, but the effect is not crucial (66 K at x = 0.1). Incorporated Ga is likely to replace Cu on the la(0, 0, 0) site.