Hysteresis effects and mesoscopic domains: Precursors for the formation of orientational glass states

Abstract

NH4I) x (KI) 1−x single crystals were investigated using proton NMR for 0.8 < x < 1. They undergo a first-order transition from the orientationally disordered hightemperature α-phase into the low-temperature β-phase. This transition exhibits a thermal hysteresis which strongly increases upon lowering x. In the α, β coexistence range evidence for nanoscopic domains was obtained using proton spin diffusion. The characteristic dimensions of the domains decrease as the critical concentration xc is approached, below which an orientational glass state is stable at low temperature. This observation indicates that close to xc the (NH4I) x (KI) 1−x orientational glasses are to be characterized as nano domain states.