Structural study of a high-temperature phase in (ND4)3D(SO4)2

The crystal structure of a new high-temperature phase in deuterated triammonium hydrogen disulphate, (ND4)(3)D(SO4)(2), was determined by the X-ray diffraction. The structure in this phase is found to be trigonal with space group R3m. The reorientation of SO4 tetrahedra occurs at the phase transition from phase I to the new high-temperature phase. The result shows that the shortest length of the O-D-O hydrogen bond which connects the two nearest adjacent SO4 tetrahedra is changed from 3.263(13) to 2.622(9) Angstrom during the structural phase transition. The mechanism of the deuterium migration in the new high-temperature phase is discussed and the new phase is confirmed to be a proton superionic conductor with respect to the crystal structure. (C) 2000 Published by Elsevier Science B.V. All rights reserved.