Determination of the Quadratic Electrostrictive Coefficients of Some Doped KCl Crystals

The quadratic electrostrictive coefficients of KCl containing substitutional impurities (KCl:Br−, KCl0.8Br0.2, KCl0.4Br0.6, KCl:Tl+, KCl:Cd2+, and KCl:Mn2+) are determined from the stress dependence of static dielectric constants. Small changes in the capacitance of the samples under the application of uniaxial stress are measured with the aid of a bridge circuit and a lock‐in amplifier. The values of the components of the electrostriction tensor of the doped systems are found to be enhanced by one to two orders of magnitude compared to those of the pure KCl crystal. The increment of the electrostrictive coefficients of KCl on doping is attributed to (i) the phenomenological description of a point defect as an anisotropic elastic dipole and the orientation of such defects; (ii) an additional deformation of the lattice arising from the reorientation of the I–V dipoles in the case of KCl containing divalent impurities. Copyright © 1992 WILEY‐VCH Verlag GmbH & Co. KGaA