NMR detection of dynamical processes in antiferroelectric nanoclusters during the order-disorder transition in NH4H2AsO4
Abstract
We study the dynamics of inorganic antiferroelectric nanoclusters formed during an order-disorder transition and demonstrate the coexistence of the two phases in a region of 2-3 K around the transition temperature TN~215 K. Single crystals of NH4H2AsO4, a model hydrogen-bonded compound, show an antiferroelectric-paraelectric transition studied by means of highly sensitive magic angle spinning 15N NMR at 21.1 T. The phase co-existence is demonstrated by a double-peak structure of the chemical shift. Two-dimensional chemical exchange spectroscopy and spin-lattice relaxation time (T1) measurements show that the clusters are dynamic with sizes ~50 nm and lifetimes approaching seconds as T->TN. Their occupancy increases rapidly to fill the crystal volume below TN. This study provides evidence for the commonality of the phase transitions in systems with electric properties and provides an improved spectroscopic method for such studies.