BaZrO3 Crucibles Research Articles

Reversible suppression of the so-called fishtail effect in ultra pure single crystals of YBa2Cu3O7?? achieved by proper oxygenation

We report on the absence of the so-called fishtail or peak effect in the magnetisation curves of properly oxygenated high purity (5N) single crystals of YBa2Cu3O7−δ. As we recently reported [1] high pressure oxygenation procedures are suitable to produce a monotonous dependence of the critical current density with the magnetic field. In this article we report furthermore how to reversibly produce or remove this effect on the same crystal by proper oxygenation methods. Along with the high purity of the samples, — due to crystal growth in non reactive BaZrO3 crucibles —, this proves that at least in pure samples the fishtail effect is due to different oxygenation states and/or oxygen distributions. In less pure samples, however, other sources for this anomaly like metallic impurities can act as an additional source for the fishtail anomaly.

Specific heat of single crystalline PrBa2Cu3O7−δ in magnetic fields

Low temperature specific heat studies on contamination free single crystals of PrBa2Cu3O7−δ (PBCO) are reported in the temperature range 1.6–40K and in applied magnetic fields ofH=0T, 2T, 5T and 7.5T. The measurements have been performed with the applied magnetic, fields parallel and perpendicular to thec-axis. The high quality of the PBCO crystals grown in BaZrO3 crucible is reflected in the observed sharp antiferromagnetic ordering peak atT N=16.6K. The shift ofT N with magnetic field is found to follow aH 2-dependence. The observed antiferromagnetic ordering of the Pr3+ ion is discussed in the framework of 3D ordering and compared with the previous reports on polycrystalline samples.

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

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.