Elastic properties of sulfanilates of Li, Na, K, Rb, Cs, Tl, NH4, CH3NH3 and C(NH2)3

Abstract

Abstract Single crystals of optical quality and dimensions up to 60 mm of sulfanilates of Li, Na, K, Rb, Cs, Tl, NH4, CH3NH3 and C(NH2)3 have been grown from aqueous solutions by controlled lowering of temperature and slow evaporation between 315 K and 290 K. All species except the sulfanilates of methylammonium and guanidinium form hydrated phases within that temperature range. Thallium sulfanilate crystallizes simultaneously in two phases, a metastable monohydrate and a stable hemihydrate. The sulfanilates of Na, K, Rb and Tl (monohydrate) possess orthorhombic symmetry, the others monoclinic symmetry. Except the cesium salt they all exhibit an inversion center. The elastic constants Cij and their derivatives Tij = d log Cij /dT, T temperature, have been determined from ultrasonic resonance frequencies of thick plates and their variation with temperature, respectively. In addition, the tensor of thermal expansion has been measured. The anisotropy of the longitudinal elastic stiffness shows a close relation to the arrangement of the sulfanilic anions. The contribution of the hydrogen bonds to the elastic stiffness is clearly recognizable. The structurally inhomogeneous group obeys to a large extent the rules governing the mean elastic and thermoelastic behaviour of ionic crystals.