Raman spectra of the B mode of the ferroelastic compound Rb₄LiH₃(SO₄)₄ as a function of temperature

Aktas, Oktay (2008) Raman spectra of the B mode of the ferroelastic compound Rb₄LiH₃(SO₄)₄ as a function of temperature. Masters thesis, Memorial University of Newfoundland.

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Abstract

Raman scattering measurements were performed on the ferroelastic compound Rb₄LiH₃(SO₄)₄ to determine whether the phase transition at Tc = 132 K is proper or pseudoproper ferroelastic. A double grating spectrometer was used to measure the frequency of the Raman active B mode at 31 cm⁻¹ in Rb₄LiH₃(SO₄)₄ as a function of temperature using two different scattering geometries. Right-angle measurements were performed between 20 K and 295 K whereas the temperature range for back scattering measurements was from 60 K up to 285 K. Our Raman measurements reveal that the square of the frequency of the optical B mode at 31 cm⁻¹ shows two linear temperature dependencies corresponding to temperatures above and below Tc. This behavior has been analyzed using a pseudoproper ferroelastic Landau Model which accounts well for the temperature dependence of a soft optical mode. Our Raman investigation clearly indicates that the nature of the ferroelastic phase transition in Rb₄LiH₃(SO₄)₄ is pseudoproper ferroelastic.

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