Abstract

Quadratic electrostrictive effects of both longitudinal and transverse type have been measured on LiF, NaF, NaCl, NaBr, KCl, KBr, KI, RbCl, RbBr and RbI single crystals with an improved frequency-modulation technique with a 100 MHz oscillator. The three independent tensor components d1111, d1122, d1212, defined as dijkl = 1/2 2ij/EkEl have been determined for all these crystals. ij are the components of the strain tensor and Ek the components of the electric field vector. All longitudinal components d1111 and all 'shear' components d1212 are negative; all transverse components d1122 are positive. The electric field causes a volume contraction in these crystals. The theoretical values for d1111 as derived by Grindlay & Wong Canad. J. Phys. (1969), 47, 1563-1571 agree well with the experimental data. Larger discrepancies are found between the predicted and observed behaviour of d1122 and d1212. Within the isotypic crystal group of alkali halides of rocksalt type the components d1111 show a positive correlation with the dielectric constants. The appreciable electrostrictive contribution to the total electro-optical effect is discussed.