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Piezoelectric crystal of betaine–selenious acid (abbreviated as B–H 2 SeO 3 ) was studied at various temperatures by X-ray diffraction, differential scanning calorimetry, dielectric and vibrational spectroscopy methods. The latter was made by applying polarized techniques for the single crystal samples (Raman, infrared transmission and reflection spectra) and for the polycrystalline samples as well. B–H 2 SeO 3 crystallizes in non-centrosymmetric space group ( Fdd 2) of orthorhombic system and does not reveal any phase transition. The high piezoelectric effect makes this crystal a candidate for nonlinear optical applications. Detailed analysis of the polarized vibrational spectra in relation to the B–H 2 SeO 3 crystal structure is presented.

Preliminary infrared studies of the host–guest interactions in the β-hydroquinone–Xe clathrate are reported. The infrared spectra of the normal and deuterated compounds are analysed at various temperatures. Normal vibrations of the host H-bonds are found to be very sensitive on the interactions with the Xe guest atoms. The temperature induced escape of the Xe from the normal and deuterated crystals appears at different temperatures and is responsible for different changes of the γ OH and γ OD deformation mode frequencies, respectively. In both cases the β-hydroquinone crystals with empty cages are formed in the first step and then they are transformed into their α-modifications.

Polarized infrared (4000–400 cm −1 ) and Raman spectra (3600–10 cm −1 ) of betaine borate single crystal have been recorded at various temperatures. The results presented here show that both phase transitions detected in betaine borate (ferroelastic at 142.5 K and structural at 45 K) manifest themselves in vibrational spectra. The polarized infrared spectra indicated that betaine and boric acid are not planar in ferroelastic phase which is consistent with structural studies. Two optic modes affected by the ferroelastic transition in the lattice vibration region are detected. One of them having B 2g symmetry is coupled linearly with the e 5 component of the elastic stiffness tensor of the same symmetry and is assumed to be involve in ferroelastic transition. This observation points out that betaine borate belongs to the ferroelastic crystal of the optical type. The evidence of the structural transition (at 45 K) were detected in lattice vibration region.