Crystal structure and temperature dependent structural phase transitions in (Ba1-xSrx)PbO3 (x = 0, 0.2, 0.6) perovskite ceramics

Abstract

The structural properties of (Ba1-xSrx)PbO3 (x = 0, 0.2 and 0.6) ceramics were examined in a wide range of temperatures, from 14 K to 1223 K, using the X-ray powder diffraction method. The type of distortion of the pseudo-cubic perovskite cell was determined from the splitting of the main diffraction lines and from the analysis of the superlattice peaks. Temperature-induced structural phase transitions at high temperatures were observed. On the other hand at temperatures starting as low as 14 K, the examined ceramics did not show any phase transitions. The effect of Sr doping was evaluated and showed that with an increase in the amount of Sr2+ ions in the crystal lattice the number of SPT's decreases. Additionally, the temperatures at which these SPT's occur are shifted towards higher values. The following sequences of structural phase transitions, written using Glazer's notation, were proposed:I2/m (a-b0c-) → Ibmm (a-b0a-)→ I4/mcm (a0a0c-)→ Pm3¯m(a0a0a0) for BaPbO3I2/m (a-b0c-) → I4/mcm (a0a0c-) → Pm3¯m(a0a0a0) for (Ba0.8Sr0.2)PbO3and I2/m (a-b0c-)→ I4/mcm (a0a0c-)→ Pm3¯m(a0a0a0) for (Ba0.4Sr0.6)PbO3.These SPT's were used as trial models in refinement procedures based on the Rietveld method.