PHASE-DIAGRAM OF THE DIPOLAR GLASS K1-X(NH4)XI

By a combination of x-ray diffraction, Raman, and neutron-scattering measurements, the (x, T) phase diagram of the dipolar glass K1-x(NH4)xI has been derived. Three compositional ranges are observed at low temperatures. Above the critical ammonium concentration x(c), estimated between x = 0.72 and 0.82, x-dependent phase transitions occur from NaCl to CsCl cubic structures, as in pure ammonium iodide. For 0. 3 less-than-or-equal-to x < x(c) an orientational glassy phase is characterized by di polar short-range order of an anti-ferroelectric. Below x approximately 0.3, the transition is no longer collective but replaced by a single-ion freezing.