Sinter-forged YBa<inf>2</inf>Cu<inf>3</inf>O<inf>7-x</inf> superconducting ceramics from the spray-roasted powders

The effect of applying a uniaxial stress, while varying the temperature and the time of sinter-forging, on the microstructure and critical current density of the sinter-forged YBa2Cu3O7-x ceramics has been investigated. Spray-roasted powders from a nitrate-based feed solution were prepared as the starting materials. By applying a relatively low uniaxial stress (2 MPa), the sintered density increased up to 95% of the maximum value. Critical current densities of between 360 and 420 A cm-2 were obtained for the sinter-forged samples which are significantly higher than values reported for pressureless-sintered samples prepared from solid-state reacted powders (typically 70 A cm-2). This increase in the density of the material and the critical current density can be explained by the alignment of the elongated YBa2Cu3O7-x grains under applied uniaxial stress during sintering. The elongated YBa2Cu3O7-x grains have been characterized by transmission electron microscopy. © 1991 Chapman and Hall Ltd.