VIBRATIONAL PROPERTIES OF DOUBLE TUNGSTATES OF THE M(I)M(III)(WO4)(2) FAMILY (M(I)=LI, NA, K - M(III)=BI, CR)

Infrared and Raman spectra of polycrystalline double tungstates M(I)M(III)(WO4)(2), where M(I) = Li, Na, K; M(III) = Bi, Cr, were measured at room temperature in the range 30-1000 cm(-1). Factor group analysis was performed and the results of these calculations were used to determine the nature of the observed modes. The coordination around the tungsten atom depends on the type of cation and is either tetrahedral or octahedral. Profound differences between vibrational spectra of tetrahedral and octahedral systems are observed. Comparing IR and Raman spectra, we assiged the vibrations above 250 cm(-1) as internal tungsten-oxygen vibrations and those below 250 cm(-1) as external vibrations. (C) 1995 Academic Press, Inc.