DTA and X-Ray Analysis on Phase Transitions and Compatibility Relationships in the Pseudobinary System Barium Metasilicate-Barium Metagermanate

Abstract

The polymorphic transformations in pure barium metasilicate and barium metagermanate have been investigated by DTA and X-ray methods. The results were used to clarify some uncertainties which exist in the published data. An endothermic heat-effect in β-BaSiO₃ was observed by DTA at 1275°C which was found to be pronounced in presence of BaGeO₃. The low-temperature α-form of BaGeO₃ transforms to a high- temperature β-form at 1180°C. In both compounds the transformation is reversible. BaSiO₃ and BaGeO₃ form a continuous series of solid solution with one another. Solidus and liquidus curves determined from DTA results indicate that there is no maxima and minima present in the BaSiO₃-BaGeO₃ system. The transformation temperature of BaSiO₃ at 1275°C remains unchanged in presence of BaGeO₃ but small addition of BaSiO₃ stabilises the high-temperature form of BaGeO₃.