187Re, 14N, and 2H nuclear quadrupole couplings in NH4ReO4: Evidence for a possible phase transition

Abstract

The nuclear quadrupole couplings of the 187Re, 14N, and 2H nuclei in NH4ReO4 have been measured over a wide range of temperatures. The 187Re nuclear quadrupole resonance has been observed throughout the previously reported ’’wipeout’’ range of temperature, showing that disappearance of the resonance is due to gradients of temperature and strain in the sample. The pressure dependence of 187Re quadrupole resonance has been measured as a function of temperature between 77 and 362 K. The slope of the graph of (∂ν/∂P)T versus temperature is indicative of a continuous phase transition at this temperature. The nature of the phase transition and its relationship to other phenomena in NH4ReO4 is unclear.