NEUTRON POWDER DIFFRACTION STUDY OF (ND4)(2)SECL6 UNDER HIGH-PRESSURE

The phase transition (T-trs = 48 K) of (ND4)(2)SeCl6, which exhibits a strong isotope effect, has been studied by neutron powder diffraction under high pressure. Data of the high-temperature phase were collecte d on HRPD at ISIS under helium gas pressure of 480 MPa at 63 K. The Ri etveld analysis and Fourier contour map revealed that the D atom of th e ND4+ ion is broadly disordered around the C-3-axis of the cubic latt ice at lower pressure and tends to be localized on the axis at higher pressure. (C) 1998 Published by Elsevier Science B.V. All rights reser ved.