Infrared, Raman, electrical and thermal analysis of lithium sulphate monohydrate single crystals

Abstract

In this work, single crystals of lithium sulphate monohydrate were grown by slow evaporation technique. Structural studies of the grown crystals were carried out by powder X-ray diffraction technique showing a monoclinic structure. Effect of temperature on the vibrational modes of different groups was observed and analyzed by Fourier transform infrared and Raman spectroscopy. The temperature dependent dielectric behaviour and ac conductivity of the grown crystals were also studied. The effect of temperature on the vibrational spectra as observed by Fourier transform infrared and Raman spectroscopy were correlated with the electrical behavior of the crystals. The relaxation studies were also undertaken using the complex-modulus M* formalism which showed a thermally activated relaxation caused by the hopping motion of H+ ions in the crystal. All the observed characteristics were found to be closely related with water loss in the crystal structure. Thermal analysis of the grown crystal was carried out by using differential scanning calorimetric technique yielding various thermodynamic parameters such as ΔH, ΔS and ΔCp. The activation energy for the dehydration step of lithium sulphate monohydrate was also evaluated by using Coats-Redfern integral method.