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Vibrational spectroscopic studies of the ferroelectric LiRbSO 4
Author(s) -
Chary B. Raghunatha,
Bhat H. L.,
Chandrasekhar P.,
Narayanan P. S.
Publication year - 1986
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.1250170113
Subject(s) - raman spectroscopy , ferroelectricity , phase transition , rubidium , laser linewidth , soft modes , chemistry , phase (matter) , molecular vibration , phonon , ion , condensed matter physics , molecular physics , materials science , optics , physics , potassium , laser , optoelectronics , organic chemistry , dielectric
Lithium rubidium sulphate, LiRbSO 4 (LRS), undergoes a sequence of four phase transitions at 166, 185, 202 and 204°C. The phase between 202 and 204°C is incommensurate. Polarized phonon Raman spectra in the frequency region of 50–1200 cm −1 are presented to identify the external and internal vibrational modes at room temperature. The internal mode frequencies of the sulphate ions are presented in the temperature region from −150 to 230°C covering all the phase transitions. The total integrated areas of the ν 1 , ν 2 and ν 4 modes show an anomalous increase across the phase transitions. The frequencies of the symmetric stretching (ν 1 ) and symmetric bending (ν 2 ) modes do not show any changes at the phase transitions, but the width of the ν 2 mode shows changes across the phase transitions. A small increase in the linewidth of the ν 2 mode observed in the incommensurate phase is attributed to the influence of the incommensurate modulation wave. A DSC thermogram showed endothermic peaks during heating at all the phase transitions. The IR spectrum recorded at room temperature showed the expected A u and B u internal modes.