Resonant Ultrasound Spectroscopy of single crystalline KH$_{2}$PO$_{4}$

TL;DR

This paper uses resonant ultrasound spectroscopy to study the elastic properties of single crystalline KH₂PO₄ during its phase transition, revealing significant anomalies and coupling effects in elastic constants.

Contribution

It provides detailed measurements of elastic constants and their anomalies across the phase transition, highlighting higher-order lattice-polarization coupling in KDP.

Findings

Significant softening of elastic constants $C_{11}$, $C_{12}$, and $C_{13}$.

Stiffening of $C_{66}$ and minima in $C_{33}$ and $C_{44}$ at transition.

Sudden softening of bulk modulus $B$ at transition.

Abstract

This study employs resonant ultrasound spectroscopy (RUS) to investigate the elastic properties of single crystalline KH$_{2}$PO$_{4}$ (KDP) through the paraelectric to ferroelectric phase transition. Noteworthy anomalies are observed in selected resonance modes and their corresponding mechanical quality factors ($Q$) around the transition temperature. The thermal evolution of elastic constants ($C_{ij}$) across the phase transition reveals a significant softening of $C_{11}$, $C_{12}$, and $C_{13}$, accompanied by a stiffening in $C_{66}$. Additionally, both $C_{33}$ and $C_{44}$ exhibit a minimum value at the transition. This anomalous behavior of all elastic constants ($C_{ij}$) across the phase transition suggests the involvement of higher-order coupling between the lattice and polarization in the KDP crystal. Furthermore, the bulk modulus ($B$) undergoes a sudden softening precisely at the transition, while the shear modulus ($G$) initially softens and subsequently stiffens across the transition.