This study employs resonant ultrasound spectroscopy to investigate the elastic properties of single crystalline KH₂PO₄ (KDP) through the paraelectric to ferroelectric phase transition. Noteworthy anomalies are observed in selected resonance modes and their corresponding mechanical quality factors (Q^-1) around the transition temperature. The thermal evolution of elastic constants (C_ij) across the phase transition reveals a significant softening and stiffening behavior. The 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.

本研究采用共振超声光谱法研究单晶 KH ₂ PO ₄ (KDP) 从顺电到铁电相变的弹性特性。在选定的共振模式及其在转变温度附近相应的机械品质因数 ( Q ^{-1 )}中观察到值得注意的异常现象。整个相变过程中弹性常数 ( C _ij )的热演化揭示了显着的软化和硬化行为。相变过程中所有弹性常数 ( C _ij )的反常行为表明 KDP 晶体中晶格和极化之间存在高阶耦合。此外，体积模量 ( B ) 在过渡处精确地经历突然软化，而剪切模量 ( G ) 最初软化，随后在整个过渡过程中变硬。