IMPLICATIONS OF THE Y2O3-BAO-CUO LIQUIDUS FOR PROCESSING PURE YBA2CU3O7-X MATERIAL

Results relating to the liquidus relationships in the CuO-rich corner of the 1/2Y2O3-BaO-CuO phase diagram were used to identify the partial meltings occurring in Y-Ba-Cu-O powders at temperatures below the peritectic decomposition of the YBa2Cu3O7-x compound. The production of this compound in three atmospheres with different oxygen potentials was followed by X-ray diffraction and differential scanning calorimetry. The origin of the partial meltings in these powders was found in the failure of the synthesis to be complete (i.e. to reach the equilibrium state) at temperatures below the solid-liquid phase transitions, implying the presence of the compounds YBa2Cu3O7-x, BaCuO2 and CuO. This difficulty is overcome if the powders are annealed in an O2 atmosphere which allows treatment temperatures as high as 940-degrees-C. Sintering of such powders up to 1000-degrees-C is not promoted by a liquid phase. Differential scanning calorimetry proved to be an easy and valuable method for checking the purity of the YBa2Cu3O7-x compound.