Crystal Growth and Elastic Properties of Hopeite, Zn3(PO4) · 4 H2O

Abstract

AbstractSingle crystals of orthorhombic Zn3(PO4)3 · 4 H2O of optical quality with dimensions up to 12 × 10 × 8 mm were grown from aqueous solutions of ZnSO4 and NaH2PO4 by controlled diffusion of NH3 into the solution. The elastic constants cij and the thermoelastic constants Tij = dcij/dT, T temperature, were determined from ultrasonic resonance frequencies of thick plates in the range between 5 and 40 MHz and between 250 and 320 K. In respect to the longitudinal elastic stiffness hopeite behaves quasi isotropically, however, the elastic shear stiffness shows a large anisotropy of about a factor 2.5. Above 260 K the shear stiffness c66 possesses a quite anomalous temperature dependence (T66 > 0). Further, the linear thermal expansion reveals a strong anisotropy (α11 = −3.3, α22 = 3.4, α33 = 33 · 10−6/K).