HYSTERESIS EFFECTS AND MESOSCOPIC DOMAINS - PRECURSORS FOR THE FORMATION OF ORIENTATIONAL GLASS STATES

(NH4I)(x)(KI)(1 - x) single crystals were investigated using proton NM R for 0.8 < x < 1. They undergo a first-order transition from the orie ntationally disordered high-temperature alpha-phase into the low-tempe rature beta-phase. This transition exhibits a thermal hysteresis which strongly increases upon lowering x. In the alpha, beta coexistence ra nge evidence for nanoscopic domains was obtained using proton spin dif fusion. The characteristic dimensions of the domains decrease as the c ritical concentration x(c) is approached, below which an orientational glass state is stable at low temperature. This observation indicates that close to x(c) the (NH4I)(x)(KI)(1 - x) orientational glasses are to be characterized as nano domain states.