# Polymorphism of BaTeO3 under High Pressure: Single-Crystal Structure Analysis and Characterization of HP-BaTeO3

## TL;DR

A new high-pressure form of barium tellurate was created and analyzed, showing structural and optical differences from its normal-pressure version.

## Contribution

The discovery and characterization of a new high-pressure polymorph of BaTeO3 with distinct structural and electronic properties.

## Key findings

- HP-BaTeO3 crystallizes in the monoclinic space group P21/c with stacked trigonal pyramidal [TeO3]2– units.
- HP-BaTeO3 has a widened bandgap compared to BaTeO3(I) due to changes in orbital overlap and lone pair orientation.
- HP-BaTeO3 is metastable and undergoes a phase transition to BaTeO3(I) at around 550 °C.

## Abstract

A new high-pressure
polymorph of barium tellurate, HP-BaTeO3, was synthesized
using multianvil high-pressure/high-temperature
techniques (4 GPa, 900 °C). The compound crystallizes in the
monoclinic space group P21/c and consists of stacked trigonal pyramidal [TeO3]2– units interconnected by secondary bonds. Structural
analysis identifies significant differences between HP-BaTeO3 and its ambient-pressure polymorph, BaTeO3(I), including
a doubling of the c-axis and additional secondary
bonding within the bc plane. The optical properties
of HP-BaTeO3 were investigated using ultraviolet–visible
spectroscopy, revealing a widened bandgap compared to BaTeO3(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-BaTeO3, with a phase transition
to BaTeO3(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.