The use of BaZrO 3 crucibles in crystal growth of the high- Tc superconductors Progress in crystal growth as well as in sample quality

Abstract

Home-made BaZrO3 crucibles have been used as a crucible material for solution growth of single crystals of REBa2Cu3−δ (RE - Y, Er, Dy, Pr) and of Y1−xPrxBa2Cu3O7−δ single crystals (0 ≤ x ≤ 1). As we recently reported [Physica C 245 (1995) 245], this new crucible material does not react with the melts commonly used as flux [ A. Erb, PhD. thesis, Universitat Karlsruhe (1994) ]. As a consequence, the composition of the melt is not altered during crystal growth and the impurity content in the single crystals is much smaller than for crystals grown in other crucible materials. The absence of corrosion also makes the crystal growth far more efficient; thus it was worthwhile to grow crystals using high-purity (5N) starting materials, in order to further enhance their quality. The high quality of the 123 crystals grown in BaZrO3 crucibles is reflected in their physical properties. As an example, the first observation of the flux lattice with STM experiments on the 123 superconductors has been performed on an uncleaved crystal grown in BaZrO3 without any surface conditioning, thus revealing superconducting behaviour up to the uppermost layer of the crystal. Another example is furnished by low-temperature specific heat measurements: besides a very narrow superconducting transition, these measurements show the absence of the upturn usually attributed to flux inclusions and hence to magnetic ordering of the flux component BaCuO2 These results prove that the quality of 123 single crystals has been considerably improved by using BaZrO3 crucibles.