Ferroelectric phase transition and crystal asymmetry monitoring of $SrTiO_3$ using quasi $TE_{m,1,1}$ and quasi $TM_{m,1,1}$ modes

TL;DR

This study uses microwave dielectric spectroscopy with specific modes to monitor ferroelectric phase transitions and crystal asymmetry in SrTiO3, revealing multiple phase transitions and the soft-mode behavior.

Contribution

It introduces a novel microwave mode-based method to detect ferroelectric and antiferroelectric transitions in SrTiO3 with high precision.

Findings

Ferroelectric transition at around 51 K.

Antiferroelectric transition at 105 K.

Quantum stabilization of the paraelectric phase below 5 K.

Abstract

Dielectric spectroscopy of $SrTiO_3$ single crystal over a broad range of microwave frequency using quasi $TE_{m,1,1}$ and quasi $TM_{m,1,1}$ modes reveals crystal asymmetry from typical measurement of $Q$-factor, transmission or frequency characteristics in continuous cooling down to a few Kelvin. The properties of the modes due to the crystal asymmetry is validated by implementing a quasiharmonic phonon approximation. The observed ferroelectric phase transition temperature is around $51~K$, and quantum-mechanical stabilization of the paraelectric phase arises below $5~K$ with very high permittivity. Also, an antiferroelectric distortive transition was indicated at $105~K$. Landau's theory of correlation length supports the observation of an extra loss term so the transition may be identified near the $Q$-factor maxima or transmission maxima, depending on the other loss terms present in the cavity. Thus, the ferroelectric phase transition with respect to temperature may be identified when this extra-loss term causes a discontinuity in the derivative of the temperature characteristic near the minimum of total cavity loss (maxim Q-factor or maximum transmission temperature characteristic). This temperature is confirmed by transmission amplitude variation under 200 V dc electric field showing existence of the soft-mode. These measurements support a typical polarization model and explicit temperature dependency of the soft-mode incorporating an imaginary frequency.