AMMONIUM DYNAMICS AND STRUCTURAL PHASE-TRANSITION IN K1-X(NH4)(X)I MIXED SALTS AT 10 K

The neutron diffraction (ND) and inelastic scattering (IINS) spectra o f the K1-x(NH4)(x)I solid solutions (0.0 less than or equal to x less than or equal to 1.0) at 10K were measured simultaneously by the TOF m ethod. Transition from the disordered alpha-phase to ordered gamma-pha se was observed, at x approximate to 0.75, with increasing ammonium co ncentration. Four inelastic bands observed at 2.5, 9, 20 and 30 meV fo r the alpha-phase, and two bands at around 20 and 36.5 meV for the gam ma-phase, are due to ammonium dynamics in crystalline lattice. The low -energy excitations in the disorder phase, at 2.5 meV, were not observ ed in previous investigations.