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 in the ab, ac, and bc planes. Variation of selected mode velocities with temperature establishes the reported ferroelectric phase transition in this crystal at 224 K.

Zinc tris(thiourea) sulphate (ZTS) single crystals possess excellent nonlinear optical properties and are nearly 1.2 times more efficient than potassium dihydrogen phosphate in optical harmonic generation. Large single crystals of this material have been grown from aqueous solution. All nine second order elastic stiffness constants of this orthorhombic crystal have been determined by measuring the velocity of propagation of ultrasonic waves of longitudinal and transverse polarizations along specific symmetry directions. The McSkimin Δt correction has been applied for better accuracy of velocity values. The corresponding elastic compliance constants and Poisson’s ratios have also been evaluated. Planar plots of phase velocity, group velocity, slowness, Young’s modulus, and linear compressibility have been drawn to display the anisotropy of wave propagation in the crystal. The bulk modulus and volume compressibility of this crystal have been evaluated from the elastic constant data. Variation of a selected number of elastic constants with temperature in a limited range have also been measured and reported.

Many organic crystals with orthorhombic symmetry exhibit electro-optic, ferroelectric, and triboluminescence properties. The potassium salt of phthalic acid (KAP), with the formula C8H5O4K, finds application in soft x-ray spectroscopy due to its large d spacing and has been reported to be piezoelectric as well. KAP crystallizes into orthorhombic structure with space group Pca21 All nine elastic constants of KAP have been determined by measuring the velocity of longitudinal and transverse ultrasonic waves propagating along different symmetry directions. Velocities have been measured by the ultrasonic pulse echo overlap technique by injecting waves generated by quartz transducers through a suitable bonding medium into the crystal. The McSkimin Δt correction has been applied to determine the velocities accurately. The temperature variation of selected elastic constants over the range 300–420 K has also been measured and reported.

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