Neutron scattering studies on superionic AgI-CsI-(CH ₃ ) ₄ NI glasses

Quasielastic and inelastic neutron scattering from AgI-CsI-(CH ₃ ) ₄ NI and AgI-CsI-(CD ₃ ) ₄ NI superionic glasses were measured as a function of temperature. At the lowest temperatures, vibrational modes from internal motion of (CH ₃ ) ₄ N ⁺ or (CD ₃ ) ₄ N ⁺ were observed above 15 meV. Below 20 meV, a broad peak typical of AgI-containing glasses was observed, which showed significant temperature dependence. This mode is attributable to the vibrational motion of localized Ag ⁺ ions. Above 173 K, quasielastic scatterings were seen below 2 meV; these were fitted by the sum of a single Lorentzian, an elastic peak and background components. The half-width at half-maximum (HWHM) of the Lorentzian component was almost Q-independent at higher Q values, and its temperature dependence was lower than the value expected from dc conductivity. This quasi-elastic component may be attributed to the local hopping of Ag ⁺ in the AgI cluster of the glass and/or the rotational motion of (CD ₃ ) ₄ N ⁺ ions.