Elastic properties of di-ammonium hydrogen citrate single crystals: an ultrasonic study

Many organic crystals with orthorhombic symmetry are non-centrosymmetric, exhibiting electro-optic, ferroelectric and triboluminescence properties. The ammonium salt of citric acid, di-ammonium hydrogen citrate, belongs to this group, which is reported to be piezoelectric and triboluminescent. All the nine second-order elastic stiffness constants of this single crystal have been determined from ultrasonic velocity measurements employing pulse echo overlap technique. The anisotropy of elastic wave propagation in this crystal has been demonstrated by plotting the phase velocity, Youngʹs modulus and linear compressibility surfaces. The relevant values of Poissonʹs ratios have been evaluated and reported. Variation of selected elastic constants with temperature have been measured and reported.