Incommensurate phase in tetramethylammonium tetrachlorozincate: Evidence from internal modes

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Abstract
Temperature‐dependent vibrational Raman studies of tetramethylammonium tetrachlorozincate [(TMA)2ZnCl4] are reported together with the assignments of the observed bands in all the six polarization geometries at room temperature in phase I, which is orthorhombic with a space group D2h16 (Z=4). Existence of the well known incommensurate phase with wave vector κ = 2/5+δ in the temperature range 296.6–280.9 K is supported by the abnormal intensity behaviour of modes of species A1 (under the point group symmetry Td for TMA and ZnCl4 ions) in X(ZZ)Y and X(YZ)Y polarization geometries. The observed intensity behaviour could be explained on the assumption that the orientations of TMA and ZnCl4 ions are governed by the incommensurate modulation in the Z‐direction.