ISOTHERMAL CRYSTAL-GROWTH OF YBA2CU3O7-X IN BAO-CUO-CUO0.5 FLUX MELTS AT REDUCED OXYGEN PARTIAL PRESSURES

Mixtures with an excess of BaO/CuO are mostly used for crystal growth of YBa2Cu3O7-x where at higher temperatures considerable amounts of Cu(I) are formed. We investigated this system by thermogravimetry and differential thermal analysis, especially under reduced oxygen partial pressure, and estimated the Cu(II)/Cu(I) ratio of the melts. At reduced oxygen partial pressure the liquidus line is shifted to lower temperature and crystal growth at this temperature is possible. By varying the oxygen partial pressure the Cu(II)/Cu(I) ratio is changed, which enables isothermal crystal growth. Crystals with dimensions of 5 X 5 X 0.1 mm3 in a 5 ml melt volume grow at a constant temperature of T = 910-degrees-C and a variable oxygen partial pressure in the range p(O2) = 5 X 10(2) -2 X 10(4) Pa.