Vibrational characteristics of the alkali metal-indium double molybdates MIn(MoO4)(2) and tungstates MIn(WO4)(2) (M=Li, Na, K, Cs)

Infrared and Raman spectra of polycrystalline alkali metal-indium double molybdates MIn(MoO4)(2) (where M=Na, K, Cs) and alkali metal-indium double tungstates MIn(WO4)(2) (where M=Li, Na, K) mere measured in the range 40-1000 cm(-1) at room temperature. To determine the symmetries and nature of the observed modes a factor group analysis has been performed. The crystal structure of the compounds studied depends on the type of cation and changes from trigonal (for the caesium-indium molybdate) to monoclinic and triclinic (for the lithium and sodium derivatives). The character of the coordination sphere around the molybdenum and tungsten atoms changes from tetrahedral (for the studied double molybdates and KIn(WO4)(2)) to octahedral (for the LiIn(WO4)(2) and NaIn(WO4)(2)). The assignment of the observed bands to the respective internal and external vibrational modes is proposed. (C) 1997 Academic Press.