SINTERING STUDIES ON SUBMICROMETER-SIZED Y-BA-CU-OXIDE POWDER

The isothermal sintering behaviour of submicrometre-sized ( < 50 nm) p owders of single-phase YBa2Cu3Ox (123) and unreacted stoichiometric mi xture of submicrometre-sized ( < 50 nm) powders of BaCO3, Y2O3 and CuO (which on calcination at 1173 K gives YBa2Cu3Ox) was investigated thr ough dilatometry under different sintering atmospheres. The sintering rate of the powder compacts was impeded by the presence of oxygen. The activation energies, Q, of sintering were determined to be 1218 kJ mo l(-1) in argon, 1593 kJ mol(-1) in air and 2142 kJ mol(-1) in oxygen. A decrease in the apparent sintered density with increasing oxygen par tial pressure was also observed. X-ray diffraction and thermal analyse s (thermogravimetry and differential thermal analysis) showed no react ion during sintering of the single-phase product. Pellets fabricated f rom uncalcined powder exhibit two stages of sintering, one between 107 3 and 1173 K having an activation energy Q=627 kJ mol(-1), and a secon d one above 1173 K with Q=383.7 kJ mol(-1). A.c. susceptibility, resis tivity and critical current density were determined as a function of t he temperature of the sintered samples.