EXAFS study of glass transition in K1-x(NH4)xI

The iodine K-edge EXAFS study of K1-x(NH4)(x)I mixed crystals was performed to clarify the local structure of the dipole glass associated with the random reorientational freezing of ammonium ions. The pair-distribution function of the nearest iodine-iodine ions is strongly reduced with increasing ammonium concentration. The reduction originates in the local distortion of lattice induced by the short-range antiferroelectric order of ammonium ions. We discuss the relationship between the reorientational freezing of ammonium ions and the local distortion of lattice in comparison with the results of X-ray diffraction measurements.