Polymorphism of BaTeO 3 under High Pressure: Single-Crystal Structure Analysis and Characterization of HP-BaTeO 3

High Resolution Image Download MS PowerPoint Slide A new high-pressure polymorph of barium tellurate, HP-BaTeO 3, was synthesized using multianvil high-pressure/high-temperature techniques (4 GPa, 900 °C). The compound crystallizes in the monoclinic space group P 2 1 / c and consists of stacked trigonal pyramidal [TeO 3 ] 2– units interconnected by secondary bonds. Structural analysis identifies significant differences between HP-BaTeO 3 and its ambient-pressure polymorph, BaTeO 3 (I), including a doubling of the c -axis and additional secondary bonding within the bc plane. The optical properties of HP-BaTeO 3 were investigated using ultraviolet–visible spectroscopy, revealing a widened bandgap compared to BaTeO 3 (I), attributed to changes in orbital overlap and lone pair orientation. Thermal analysis and high-temperature powder X-ray diffraction confirmed the metastable nature of HP-BaTeO 3, with a phase transition to BaTeO 3 (I) occurring at approximately 550 °C. This study highlights the structural and electronic modifications induced by high-pressure synthesis and provides insights into the relationship between the two polymorphs.