Growth and chemical analysis of bulk Nd2-xCexCuOy single crystals

Single crystals of Nd2-xCexCuOy (0 < x < 0.17) from a family of the electro n-type superconductors have been grown using platinum crucibles by the top seeded solution growth technique. The structural quality of the crystals wa s examined by X-ray diffraction. The FWHM of the Bragg reflections for the best samples varies from 8 to 20 angular seconds. Full neutron activation a nalysis was carried out to determine the chemical composition of the as-gro wn crystals. Small cation stoichiometry deviations from ideal (NdCe)/Cu rat io are found as well as Pt substitution on the copper sublattice at a level up to 2 at% exists depending on growth conditions. The results of thermogr avimetric measurements and further annealing of samples show that the probl em of an oxygen reduction of large Nd2-xCexCuOy crystals is closely connect ed with inhomogeneity of anion distribution in the lattice possibly caused by non-optimal parameters for the reduction process and the level of impuri ties contamination. A three step reduction process which produces supercond uctivity with T-c similar to 19 K in single crystals thicker than 1 mm has been developed. (C) 1999 Elsevier Science B.V. All rights reserved.