Structural, optical and dielectric studies of lithium sulphate monohydrate single crystals

Abstract

Optical, dielectric, and thermal properties of lithium sulphate monohydrate crystals grown by slow evaporation method have been studied. The crystal structure was resolved by direct methods using single crystal X-ray diffraction data collected at room temperature and refined by full-matrix least-squares procedures to a final R-value of 0.0174. Plasma energy, Penn gap, Fermi energy and electronic polarizability of the grown crystal were calculated from single crystal XRD data. The electronic polarizability of lithium sulfate monohydrate was also calculated and compared with the theoretical data using Clausius-Mossotti equation. Optical band gap calculated from optical data for the grown crystal is 4.49 eV. Fourier Transform Infrared Spectroscopy study confirmed the presence of water in the crystal structure. The AC conductivity, dielectric constant and dielectric loss of the grown crystal were systemically investigated, showing a peak at about 130°C which could be attributed to the water molecules in the crystal structure. The anomalous dielectric properties shown by the crystal have been correlated with its thermal behavior. The title crystal obeys Jonscher's power law relation; σ(ω) = σ o + Aω s , with temperature dependent exponent s < 1. The activation energy calculated for the material is 0.24 eV and suggests protonic conduction by hopping mechanism in addition to cationic conduction by lithium ions. The micro-indentation study was also carried out which revealed that the crystal belongs to a category of soft materials.

Growth and Various Characterizations of Lithium Sulfate Monohydrate Single Crystals after Eu3+ and Tb3+ Ion Doping

“…They are attributed to the charge transfer transition of O 2− → S 6+ and O 2− → Li + transitions. [18] This band is also observed in optical absorption spectra of this crystal. In some optical absorption studies of this crystal, the 240 nm band is the cut-off wavelength.…”

“…By the extrapolation of the linear region the bandgap of Eu 3+ , Tb 3+ doped and pure LSMH crystals were calculated and it was observed to be 4.31, 4.26, and 4.38 eV, respectively, which is in agreement with the reported value. [ 18 ] Here we observed that the energy gap reduces with doping in these crystals. For this observed behavior, we can rely on two possible facts: a) the ionic radii of the dopants Eu 3+ , Tb 3+ ion are smaller than those of the parent Li + ion in the host matrix and if the particle size is smaller than the interparticle distance or when particles undergo aggregation, the Plasmon resonance shifts toward a shorter wavelength; [ 38 ] b) defect states induced in the bandgap, which is appearing as band edge and hence reducing the optical bandgap.…”

“…84‐0649). As already studied by our group, [ 18 ] current LSMH crystal has a right prism‐shaped unit cell, in which the vertices and edge centers of that are directed along the c axis, and occupied by the sulfur atoms. Here each S 6+ ion is coordinated by four O 2− ions, giving rise to the regular tetrahedra.…”

“…Further, these anionic compounds give rise to tetrahedral and octahedral cavities, and thereby accommodating Li + and H + ions, respectively. [18] Also as per the bandgap calculations carried out on these alkali sulfates, the energy levels at the valence band (VB) top are expressed by a low dispersion typical for kind of crystals, [44] hence projecting us that the chemical bond between the groups of atoms forming them is comparatively very feeble. Maximum dispersion energy-momentum plot was seen for the low levels of the conduction band (CB) in regions of the Brillouin zone.…”

“…[16] Lithium sulfate monohydrate which crystallizes in the polar space group P2 1 can be proved to be a good host material because of its good thermal, chemical, and mechanical stabilities. [17,18] LSMH can absorb the light and act as sensitizer and transfer energy to RE ions due to its wide bandgap. High transparency and the suitable refractive index of LSMH in the UV-visible region make them a possible candidate for the application in optical devices.…”