Determination of the Anisotropy of Permittivity of Quantum Paraelectric Strontium Titanate

TL;DR

This study precisely measures the permittivity of strontium titanate, revealing isotropy at room temperature and uniaxial anisotropy at low temperatures, resolving previous conflicting reports.

Contribution

It provides the first clear experimental evidence of temperature-dependent permittivity anisotropy in SrTiO3 using simultaneous mode measurements.

Findings

Permittivity is isotropic (~316.3) at room temperature.

Material becomes uniaxially anisotropic below 6 K.

Permittivity ratio reaches up to 2.4 at low temperatures.

Abstract

The dielectric properties of strontium titanate (SrTiO$_3$) have previously been reported from room temperature to low temperatures with conflicting results. In this work, precision measurement of the permittivity is undertaken by simultaneously measuring transverse electric and transverse magnetic resonant modes within a single crystal. It is unequivocally shown that the permittivity is isotropic at room temperature with a permittivity of order $316.3\pm2.2$ by measuring multiple modes of different electric field polarisations. As the crystal is cooled to 5 K and undergoes well known phase transitions, we show the material becomes uniaxial anisotropic with the ratio of the parallel to perpendicular permittivity to the cylinder z-axis of the sample as high as 2.4 below 6 K.