Quadratic electrostrictive effects in LiF, NaF, NaBr, KCl, KBr, KI, RbCl, RbBr and RbI

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 d_ijkl = ½ ∂²[epsilon]_ij/∂E_k∂E_l have been determined for all these crystals. [epsilon]_ij are the components of the strain tensor and E_k 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.