Electrochemical growth near the Ba1-xKxBiO3 (x > 0.5)-Ba1.7K1.3Bi2O7 boundary and the crystals properties

We report on the cubic Ba1-xKxBiO3 and tetragonal Ba1.7K1.3Bi2O7 phases nuc leation and stability in time under the electrochemical crystal growth cond itions from a KOH melt. BaBiO3 single-crystal plates have been used as a se ed to stimulate either oriented or epitaxial nucleation. In order to reach the maximum Ba substitution in the cubic phase crystals, a flux saturated w ith Bi2O3, has been selected to grow the x = 0.67 crystal, which reveals T- c similar to 4.5 K. Crystals of the tetragonal phase(a = 4.277 Angstrom, c = 21.885 Angstrom) up to some mm(3) in size have been grown at the same pot ential, when the Bi2O3 concentration in the flux was decreased to 9 x 10(-4 ) mol/KOH mole. New crystals of Ba0.9K0.2Bi0.9O3 belong to a cubic phase (a = 4.266 Angstrom), but are nonsuperconducting as first grown. The large cr ystals morphology, as well as magnetic properties, are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.