Determination of single crystal elastic moduli of KTb3F10 by resonant ultrasound spectroscopy

KTb 3F 10 (KTF) has been developed in recent years as a candidate Faraday rotator material because of its cubic symmetry, high figures of merit, and low absorption coefficient. While considerable efforts have focused on crystal growth and optical properties, investigations of fundamental thermodynamic behavior of KTF have been limited. Here, we report elastic moduli C 11, C 12, and C 44 of single crystalline KTF measured by resonant ultrasound spectroscopy from 280 K up to 300 K and the obtained temperature derivatives of each modulus. We additionally report the single crystal elastic moduli of the rare-earth garnet Y 3Al 5O 12 (YAG), yielding results that agree well with the prior literature. We found C 11 = 135.62 GPa, C 12 = 58.11 GPa, and C 44 = 44.81 GPa for KTF and C 11 = 332.43 GPa, C 12 = 109.58 GPa, and C 44 = 114.81 GPa for YAG at room temperature. The present results have been compared with previous experimental and theoretical results and with common oxide and fluoride optical materials, revealing the relative softness of KTF. The low elastic moduli of KTF are, in turn, responsible for its low thermal conductivity and low Debye frequency compared to other laser host materials.