Raman Spectra of Polycrystalline Lithium Sulfate, Sodium Sulfate, and Potassium Sulfate in the Pretransition Temperature Range Lower the Structural Phase Transition

Abstract

Molecular relaxation processes in lithium sulfate (Li₂SO₄), sodium sulfate (Na₂SO₄), and potassium sulfate (K₂SO₄) are studied using Raman spectroscopy (RS). The order parameter decreases in the low-temperature phase as it approaches the phase transition. For example, this is typical of a first-order phase transition close to a second-order phase transition. The existence of the pretransition region in the investigated sulfates Li₂SO₄, Na₂SO₄, and K₂SO₄ is proven.