High-pressure synthesis and characterization of a new series of V-based superconductors (Cu0.5V0.5)Sr2Can-1CunOy

A new series of high transition temperature (T-c) superconductors (Cu,V)Sr2 Can-1CunOy [(Cu,V)-12(n - 1)n-Sr, n = 3-7] was synthesized under a high-pre ssure/high-temperature condition of 6 GPa and 1300 degrees C. X-ray diffrac tion and transmission electron microscopy measurements revealed that they h ave M-12(n - 1)n-type structures with M = (Cu,V) and a stacking sequence of planes, SrO-(Cu,V)O-SrO-CuO2-(Ca-CuO2)(n-1). Simple tetragonal lattices wi thout any superstructures were observed for every member of the series impl ying a random arrangement of copper and vanadium in the (Cu,V) plane. Elect ron-probe microanalysis indicated partial substitution of strontium for cal cium in the (Cu,V)-12(n - 1)n-Sr phases. All the (Cu,V) phases gave large d iamagnetic susceptibilities at a low temperature indicating bulk nature of superconductivity. The highest T-c was found to be 107 K for the (Cu,V)-123 4-Sr phase.