Ambient-condition growth of superconducting YBa2Cu4O8 single crystals using KOH flux

Abstract: YBa2Cu4O8 is a stoichiometric oxide superconductor of T c∼80K. Unlike YBa2Cu3O7− δ , this compound is free from oxygen vacancy or twin formation and does not have any microscopic disorder in the crystal. Doping with Ca raises its T c to 90K. The compound is a promising superconductor for technological application. Up to now, single crystals have not been grown without using specialized apparatus with extremely high oxygen pressure up to 3000bar and at over 1100°C due to the limited range of reaction kinetics of the compound. This fact has delayed the progress in the study of its physical properties and potential applications. We present here a simple growth method using KOH as flux that acts effectively for obtaining high-quality single crystals in air/oxygen at the temperature as low as 550°C. As-grown crystals can readily be separated from the flux and exhibit a perfect orthorhombic morphology with sizes up to 0.7×0.4×0.2mm3. Our results are reproducible and suggest that the crystals can be grown using a conventional flux method under ambient condition. [Copyright &y& Elsevier]