Brillouin scattering investigation of the high temperature diffuse phase transition in Li₂S

Abstract

Cu have been determined from high temperature Brillouin Scattering measurements on the anti-fluorite StNctUred compound Li2S. These decrease linearly from 300 to 8WK, but above 804 Ksubstantial reductions occur in C,, and Clt. The results are interpreted in terms of normal thermal expansion and a diffuse superionic transition involving Frenkel disorder on the lithium sublattice.

Experimental Raman scattering investigation of phonon anharmonicity effects in

“…As both the analysis of the experimental data and that of the numerical calculation involve simplifying assumptions, we use the average value of 17.4 GPa for C 12 in the following. The temperature dependence of the C ij was obtained by using the results of a recent experimental high-temperature Brillouin scattering study on Li 2 S performed between 300 K and 1000 K [8]. The Brillouin frequency shift and the velocity of an acoustic mode propagating in a specific direction in a cubic crystal are related [20] by…”

“…Ionic conductivity experiments performed in our laboratory showed undoubtedly [4] the presence of this transition at around 1250 K in Na 2 S (T m 1450 K). Only recently, high-temperature experimental investigations and theoretical studies were performed on the compound Li 2 S. These include quasi-elastic neutron scattering work by Altorfer et al [5,6] and Bührer et al [7], Brillouin scattering experiments by Mjwara et al [8], ionic conductivity experiments by Carron [9] and quantum mechanical Hartree-Fock studies by Lichanot et al [10]. These experimental and theoretical studies supply evidence for a substantial thermally induced disorder of the lithium sublattice near 850 K which could be accounted for by cation Frenkel defect generation.…”

FP-LAPW investigation of mechanical and thermodynamic properties of Na2X (X = S and Se) under pressure and temperature effects

“…The alkali metal chalcogenides Na 2 X (X = S, Se) constitute a crystalline family that has shown great technological usefulness in devices requiring high ionic conductivity [1][2][3] and large fundamental energy band gaps. Apart from being used in power sources, fuel cells, gas-detectors and ultra violet space technology devices [4][5][6], these ionic compounds also play an important role in the development of photocathodes, in supporting catalytic reactions and enhancing oxidation of semiconductor surfaces [7][8][9][10][11][12][13][14].…”

Optical and Computational Studies of Elastic and Defect Properties of Materials

“…The simplest compounds which display these combined features have the fluorite or antifluorite structure. A considerable amount of work has been carried out on the alkaline-earth fluorides which have the fluorite structure, such as CaF2 and its analogues, [5, 61 and some on Li2S, an anti-fluorite compound [7]. More recently, studies have been made on the trigonal tysonite structured fluorides such as LaF3, CeF3 and NdF3 In Brillouin scattering from transparent crystals, bulk acoustic phonons modulate the permittivity and as a result of elastio-optic coupling lead to inelastic scattering of light.…”