STRUCTURE AND VIBRATIONAL PROPERTIES OF TETRAGONAL SCHEELITE NABI(MOO4)(2)

The structure of the tetragonal NaBi(MoO4)(2) crystal was determined, The space group is (I) over bar 4 = S-4(2) with cell dimensions a = 5. 267, c = 11,565 Angstrom and Z = 2, The molyhdenum atoms occupy two di fferent sites of (4) over bar symmetry, The Na+ and Bi3+ cations are s ituated on two positions with different occupancy factors and are shor t-range ordered, The IR and Raman polarized spectra are discussed on t he basis of the factor group analysis and phonon calculations. The mod ified Urey-Bradley force field and potential energy distribution were applied for three molecular models of local disorder, Polarization pro perties are explained and related to the crystal structure. (C) 1997 J ohn Wiley & Sons, Ltd.