Effect of Firing Atmosphere on the Cubic-Hexagonal Transition in Ba<sub>0.99</sub>Sr<sub>0.01</sub>TiO<sub>3</sub>

Ba0.99Sr0.01Tio3 ceramics were fired for 1 hour at a temperature from 1410° to 1460°C in H2-N2 atmospheres. A pure hexagonal phase, which was not formed by calcination in air, was obtained by firing for 1 hour at 1430°C in H2 atmosphere. A part of the oxygen in Ba0.99Sr0.01TiO3 was removed under the reducing condition, which led to the formation of the hexagonal phase. The amount of the hexagonal phase of Ba0.99Sr0.01TiO3-x increased proportionally with an increase in oxygen deficiency (x). The value of x required for stabilizing the hexagonal phase at room temperature was found to be larger than 0.008. The transition temperature from cubic to hexagonal phase of Ba0.99Sr0.01TiO3-x was higher than that of BaTiO3-x, and oxygen deficiency required for stabilizing the hexagonal phase was larger than that for BaTiO3-x. These results indicated that Ba0.99Sr0.01TiO3-x does not easily transformed into the hexagonal phase.