Thermal analysis and thermal expansion studies on high density YBa2-xLaxCu3O7-δ, 0 ≤ x ≤ 0.2

The compositions in the YBa2-xLaxCu3O7-delta (0 less than or equal to x less than or equal to 0.2) system were prepared by the solid state reaction, employing a novel high-temperature oxygen sintering route. The modified sintering route yields dense slab like microstructures with large grains. The decomposition (incongruent melting) temperature of the YBa2Cu3O7-delta (Y-123) phase was found to shift to higher temperatures with increasing oxygen partial pressure and lanthanum content. Structure remained orthorhombic up to x = 0.2 with a decrease in the orthorhombic strain ((b-a)/b). Iodometric titration indicated a systematic increase in the oxygen content with increasing lanthanum content. Thermo-gravimetric studies in various oxygen partial pressures revealed that the oxygen diffusion in to the YBa2Cu3O7-delta (E > 0.5) lattice is an exothermic event and takes place at temperatures not less than 573 K. High-temperature thermal-expansion measurements in air indicated that the nonlinearity in thermal expansion behaviour was reduced by the substitution of lanthanum. (C) 2003 Elsevier SAS. All rights reserved.