Far-infrared spectroscopic investigation of the incommensurate and commensurate phases in ferroelectric betaine calcium chloride dihydrate (BCCD)

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Abstract
We have measured the far-infrared transmission spectra of BCCD, ((CH3)3NCH2 COO CaCl2 2H2O), polarized in the (ferroelectric) y-axis in the wavenumber interval 10 cm−1≤ ν ≤ 110 cm−1 and in the temperature range 20 K≤ T ≤300 K. The temperature dependence of new bands arising in the various commensurate phases and of hard-core modes have been studied. The spectra are compared with Raman spectra. A type of symmetry for the soft mode has been proposed based on the obvious selection rules obeyed by the spectra.