Dipole Glass Phase in an Isolated Hydrogen-Bonded Mixed Crystal [(NH 4 ) 1− x Rb x ] 3 H(SO 4 ) 2 ( x = 0.58)

[(NH 4 ) 1− x Rb x ] 3 H(SO 4 ) 2 mixed crystals were investigated by dielectric constant measurement and Raman spectroscopy from room temperature to 7 K. In contrast to the result of (NH 4 ) 3 H(SO 4 ) 2 ( x = 0) showing multiple phase transitions, [(NH 4 ) 1− x Rb x ] 3 H(SO 4 ) 2 ( x = 0.58) mixed crystal does not show any remarkable dielectric anomaly but a weak dielectric dispersion below 40 K, which is characterized by the Arrhenius law. From the measurement of the Raman spectra of both crystals, it is confirmed that the [(NH 4 ) 1− x Rb x ] 3 H(SO 4 ) 2 ( x = 0.58) mixed crystal shows a global symmetry conservation between the two spectra measured at room temperature and at 20 K while the (NH 4 ) 3 H(SO 4 ) 2 crystal exhibits drastic structural changes associated with the sequence of the phase transitions. It is concluded that [(NH 4 ) 1− x Rb x ] 3 H(SO 4 ) 2 ( x = 0.58) mixed crystal shows a new dipole glass phase in the isolated hydrogen-bonded system.