Ultrasonic investigation of elastic properties and a phase transition in ferroelectric glycine phosphite NH3CH2COOH3PO3 single crystals

A detailed ultrasonic study of the elastic properties of glycine phosphite single crystals has been carried out at room temperature as well as across the ferroelectric phase-transition temperature. All 13 elastic stiffness moduli of this monoclinic crystal at room temperature have been determined by measuring the velocities of ultrasonic waves of different polarizations, propagating along, different symmetry directions using the pulse echo overlap technique. The anisotropy in elastic wave propagation is established employing polar plots of the phase velocity surfaces ih the ab, ac, and be planes. Variation of selected mode velocities with temperature establishes the reported ferroelectric phase transition in this crystal at 224 K.