IR temperature study of internal vibrations in K3Na(SeO4)(2)

Temperature variations of internal vibrations in K3Na(SeO4)(2) crystal have been observed using IR absorption spectroscopy and interpreted on the basi s of group theory predictions. The symmetry of the intermediate phase betwe en the paraelastic (3) over bar m and the ferroelastic 2/m ones (334-346 K) was determined to be (3) over bar. This finding supports the result obtain ed previously from the Raman study of the same crystal and is in agreement with the result obtained recently from X-ray diffraction at 340 K. Moreover , some critical changes in the IR spectra and some anomalous dielectric beh aviour have been observed in the 240-300 and 210-250 K temperature regions, respectively, and interpreted as connected with the transition from the hi gh temperature orientationally disordered crystal to the completely ordered crystal. (C) 2000 Elsevier Science B.V. All rights reserved.