A re-investigation of the quadratic electrostriction of alkali halides of rocksalt type

In order to clarify the reasons for the contradictory results regarding qua dratic electrostriction in alkali halides reported by various authors, we d eveloped an improved capacitive dilatometer. Employing the frequency-modula tion technique, the resolution of the experimental set-up reaches Delta l a pproximate to 2 x 10(-13) m. Various possible sources of errors could be de tected, including sample mounting, calibration faults and, in particular, e lectro-mechanical resonances caused by strong Coulomb interactions between certain components of the dilatometer. From frequency-dependent measurement s in the range 60-1200 Hz we determined the complete tensors of the quadrat ic electrostriction of LiF, NaCl, NaBr, KCI, KBr, KI, RbCl, RbBr and RbI at room temperature. The results are in reasonable agreement with values deri ved from sophisticated lattice-theoretical models. Furthermore, we studied the influence of the real structure of Li-doped KCI crystals on their elect rostrictive properties.