CU-DEFICIENCY IN LA2-XSRXCU1-YO4-DELTA SINGLE-CRYSTALS AND HOW IT AFFECTS SUPERCONDUCTING PROPERTIES

The modified TSSG (top seeded solution growth) method for growth of La 2-xSrxCu1-yO4-delta single crystals has been developed and solid solut ions with x = 0.00, 0.03, 0.04, 0.05, 0.08, 0.10, 0.11 and 0.15 have b een obtained. The dependence of the effective substitution coefficient of strontium K(s) versus Sr concentration in the melt at 1065 +/- 5-d egrees-C has been determined. The structural O-T transition is observe d at x less-than-or-equal-to 0.11. It has been found that LCO and LSCO have crystallized with Cu-deficiency which depended on overcooling (o versaturation) during crystallization. It has been shown that Cu-defic iency dominates in suppressing superconductivity in LSCO-crystals. LSC O-crystals with Cu-deficiency of less than 0.04 at./fu. demonstrate a superconducting transition with T(c) = 10-20 K (for the composition wi th 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 p ressures of up to 3 kbar.