Infrared spectra of paraelectric and ferroelectric CsH2PO4

ir spectra are reported for polycrystalline CsH₂PO₄ above and below the transformation temperature, 153 K. Three absorption bands at 1760 cm^-1 2350 cm^-1 and 2800 cm^-1 are assigned to -OHO- vibrations. Whilst the 2350 cm^-1 band remains essentially unaltered, the 1760 cm^-1 band splits into multiplets and the 2800 cm^-1 band shifts to lower frequency on cooling below 153 K. A broad band centred at 3240 cm^-1 is found to exist in the ferroelectric phase and is associated with the -OHO- mode involving the H(2) proton ordered below the transition.