A new method of YBa2Cu3O7−xsingle-crystal growth in Al2O3crucibles with layered protective covers

A new method of YBa2Cu3O7−x(YBCO) crystal growth is presented, which uses Al2O3crucibles with protective covers. The protective cover includes at least two ceramic layers, which are composed of (Y2O3+ Y2BaCuO5) mixtures sintered under proper conditions. The layer nearest to the Al2O3crucible wall is enriched by Y2O3and protects the crystallization zone against Al into pollution. The layer nearest to the YBCO melt consists of a pure Y2BaCuO5phase and provides the introduction of Y the reaction volume via partial dissolution. Large crystals of 3.2 × 3.2 × 0.2 mm3of high purity with low residual microwave losses have been grown by this technique from YBa2Cu3O7−x+ Ba2.8Cu7.2Oxflux. This method can be extended for other single crystals and melted material. The protective covers may be prepared also on crucibles of other materials, if they have a good thermal stability and can hold several thermal cycles.