STRUCTURAL PHASE-TRANSITION AND CRYSTAL-STRUCTURE OF NA3H(SO4)(2) IN THE LOW-TEMPERATURE PHASE

Differential scanning calorimetry and X-ray diffraction measurements a re performed on trisodium hydrogen disulphate, Na3H(SO4)(2), crystals at low temperatures. A structural phase transition is found at 178(3) K. The space group symmetry (triclinic P1) and the crystal structure a re determined at 139 K in the new low-temperature phase. II is found t hat the H atoms on the O-H-O hydrogen bond are not located on the cent er of the bond. By the shift of the S atom from the center of the SO4 tetrahedron, it points out that Na3H(SO4)(2) crystal in the new phase is possible to be ferroelectric with the dipole moment almost along th e [(1) over bar 2 0] direction.