Cu-deficiency in La2−xSrxCu1−yO4−δ single crystals and how it affects superconducting properties

Abstract The modified TSSG (top seeded solution growth) method for growth of La 2− x Sr x Cu 1− y O 4− δ single crystals has been developed and solid solutions with x = 0.00, 0.03, 0.04, 0.05, 0.08, 0.10, 0.11 and 0.15 have been obtained. The dependence of the effective substitution coefficient of strontium K s versus Sr concentration in the melt at 1065±5°C has been determined. The structural O-T transition is observed at x ⩽0.11. It has been found that LCO and LSCO have crystallized with Cu-deficiency which depended on overcooling (oversaturation) during crystallization. It has been shown that Cu-deficiency dominates in suppressing superconductivity in LSCO-crystals. LSCO-crystals with Cu-deficiency of less than 0.04 at./f.u. demonstrate a superconducting transition with T c =10–20 K (for the composition with x =0.15). LSCO-crystals with Cu-deficiency of more than 0.04 at./f.u. are non-superconducting even after thermal treatment under oxygen pressures of up to 3 kbar.