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 ran
dom reorientational freezing of ammonium ions. The pair-distribution functi
on of the nearest iodine-iodine ions is strongly reduced with increasing am
monium concentration. The reduction originates in the local distortion of l
attice induced by the short-range antiferroelectric order of ammonium ions.
We discuss the relationship between the reorientational freezing of ammoni
um ions and the local distortion of lattice in comparison with the results
of X-ray diffraction measurements.