The low frequency Raman spectrum in relation to the phase transition of KH3(SeO3)2

Abstract

The low frequency Raman spectrum of KTS has been recorded and analysed above Tc at 1 bar and 8 kbars, in the B3g geometry which corresponds to the low temperature static deformation. The spectra clearly show the existence of a proton mode below 50 cm-1; the analysis shows that quantum effects and the proton coupling with an optic mode around 40 cm-1 play minor roles in the transition mechanism. On the contrary, the interaction between the protons turns out to be classical in nature, their dynamics is of the relaxation type (with a relaxation time τ = (27 cm-1)-1) and their coupling with the B3g deformation is very important : all those effects stress the large difference between KH2PO4 and KTS in spite of the large sensitivity, to deuteration, of their critical temperature Tc