Single Crystals of CuxMo6Se8: Growth, Compositional Inhomogeneity and Superconducting Properties

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Abstract
Single crystals of Chevrel-type compounds Cu x Mo6Se8 (0≤x≤2.4) have been grown by the Bridgman method under a He pressure of 50∼100 atm, The content of copper x is observed to be gradually enriched as the crystal growth proceeded. The superconducting transition temperature T c is determined as a function of x. The results are summarized into three regions; 6.0\lesssimT c\lesssim6.5 for 0≤x\lesssim0.7, 6.0\lesssimT c\lesssim5.0 for 0.7<x\lesssim2.0 and T c2.0. The transition temperature width, Δ T c, increases with increasing x. The results of XPS indicate that no marked change occurrs with variation of x. The oxidation from Cu1+ to Cu2+ is observed by XPS on the surface of the pulverized crystals.