Precision Multi-Mode Dielectric Characterization of a Crystalline Perovskite Enables Determination of the Temperature-Dependent Phase Transitions

TL;DR

This study uses high-precision multi-mode microwave resonances to characterize the temperature-dependent dielectric phase transitions in a single crystal of Strontium Titanate, revealing anisotropic permittivity changes at specific low temperatures.

Contribution

It introduces a multi-mode microwave measurement technique for precise, non-destructive characterization of dielectric anisotropy during structural phase transitions in perovskite crystals.

Findings

Permittivity is isotropic at room temperature with a value of 316.3±2.2.

Dielectric anisotropy appears below 105 K with uniaxial symmetry.

Biaxial anisotropy emerges below 51 K during the orthorhombic phase transition.

Abstract

Simple perovskite crystals undergo structural phase transitions on cooling to low temperatures, which significantly change the material properties of the crystal. In this work we rigorously characterize the temperature evolution of permittivity of a perovskite crystal as it undergoes phase transitions. In particular, we have undertaken precision measurements of a single crystal of Strontium Titanate from 294.6 K to 5.6 K, by measuring the frequency of multiple microwave transverse electric and magnetic resonant modes simultaneously. The multi-mode microwave measurement technique of resonant frequency used in this work allows high precision determination of any induced anisotropy of the permittivity as the crystal undergoes structural phase transitions. Compared with previous results we unequivocally show that the permittivity has an isotropic value of $316.3\pm2.2$ at room temperature, consistent with its well-known cubic structure, and determine the onset of dielectric anisotropy as the crystal is cooled to lower temperatures. We show that the crystal exhibits uniaxial anisotropy in the permittivity below 105 K when the structure becomes tetragonal, and exhibits biaxial anisotropy in the permittivity below 51 K when the structure becomes orthorhombic.