VIBRATIONAL STUDY OF THE DISORDERED PARAELASTIC HIGH-TEMPERATURE PHASE OF THALLIUM DIHYDROGEN ARSENATE, TLH2ASO4

Infrared and Raman spectra of polycrystalline thallium dihydrogen arse nate were investigated in the 10-4000 cm(-1) wavenumber range as a fun ction of temperature between 300 and 463 K. The occurrence of a high-t emperature phase (I) above 370 K is well evidenced by shifts in both i nternal and external vibrational parameters, The vibrational behaviour of phase I is very similar to that of the corresponding phase in TIH2 PO4, Under specific conditions the compound melts without decompositio n; the Raman spectrum of the molten state was also analysed, The site symmetries C-1 and C-2 of the whole disordered hydrogen bonded network in the phase I are not observed and the hydrogens appear still ordere d, The hydrogen bonds are always strong and no superionic conductivity could be deduced, Some OH mode behaviours appear different from those in the phosphate compound.