Vibrational characteristics of the double oxygen bridge in the NaIn(WO4)2 and NaSc(WO4)2 tungstates with wolframite structure

The normal coordinate analysis of the tungsten-oxygen core in NaIn(WO4)(2) and NaSc(WO4)(2) crystals was performed. The Urey-Bradley force field and potential energy distribution (PED) were applied in the internal and external phonon calculations for the W4O22Na2In2 molecular system. The dynamics of the asymmetric WO2W oxygen bridge as well as terminal W=O bonds were analyzed and discussed. The vibrational characteristics of the oxygen double bridge bond, i.e. vibration energy, symmetry, force constants, FED, atomic displacements, direction of the transition dipole moments and mean square amplitudes were obtained and discussed. The theoretical considerations were based on the polarized IR and Raman spectra of the materials studied. (C) 1999 Elsevier Science B.V. All rights reserved.