Manipulation of Ba-O layers inducing orthorhombic-tetragonal phase transition in YBa_2-xSr_xCu₃O_6.7

Abstract

Monophasic oxides of the type YBa_2-xSr_xCu₃O_6.7 (0.0<x<0.8) and YBa_2-xSr_xCu₃O_7.0 (0.0<x<0.8) have been synthesized. X-ray diffraction studies reveal an orthorhombic to tetragonal phase transition at x=0.4 in the O_6.7 series, the oxides are superconducting; T_c's from 52 (x=0.0) to 37 K (x=0.8). The O_7.0 oxides are all orthorhombic with T_c's from 93 (x=0.0) to 81 K (x=0.8). Factors leading to the phase transition are discussed.