EXAFS Study on the Glassy State of K_1-x(NH₄)_xI Mixed Crystals

Abstract
EXAFS study was performed on K_1-x(NH₄)_xI mixed crystals with x=0, 0.48 and 0.68 in order to clarify a local structure of the dipole-glassy state. From the analysis with k_X(k) spectra, broadening of the peaks indicating the distance between the nearest iodine ions was observed in the glassy state. The back-Fourier transforms of the iodine ions was well reproduced by the one-shell model in the whole concentration and temperature range. The Debye-Waller factor increases largely with increasing concentration, which is caused by the static disorder. The result indicates existence of the local distortion of lattice formed by iodine ions which is induced by reorientational freezing of ammonium ions with only short-range antiferroelectric correlation.