| Abstrakt: |
The paper presents theoretical investigations of the elastic and acoustic properties in crystals forming the solid solution system CuGa(S1 − xSex)2 . The structures with varying selenium content, x = 0, 0.25, 0.5, 0.75, and 1, were examined. Employing the supercell method, a series of solid solutions were modeled by replacing sulfur atoms with selenium atoms in the CuGaS2 crystal structure. The generated substitution structures underwent geometry optimization using density functional theory (DFT) in conjunction with the BFGS algorithm, describing the exchange-correlation interactions through generalized gradient approximation (GGA). The optimized structures of the solid solutions were found to be in good agreement with the available experimental data, with a slight overestimation of parameters, attributed to the known features of the GGA functional. The elastic constants matrix Cij for tetragonal symmetry was calculated, demonstrating compliance with Born's mechanical stability criterion for all compositions investigated. The evaluation of the material's elastic characteristics with changing composition revealed that the coefficients and C33 exhibited nearly twice as large values compared to the shear coefficients. Notably, the C11 coefficient reached 104.79 GPa, while the minimum value was obtained for C44 at 51.29 GPa. Isomorphic replacement of sulfur with selenium atoms resulted in a monotonic decrease in the elastic constants Cij. Employing the Green-Christoffel equation, the acoustic wave propagation velocities in a number of crystals were calculated using a home-made program written in Python. Acoustic wave velocities v were computed in (100) and (001) planes, with the highest observed velocity v max = 5586 m/s corresponding to the longitudinal acoustic wave (LA) in the (001) plane. The isomorphic replacement of S → Se resulted in a monotonic reduction in the propagation velocity v of acoustic waves within the investigated solid solution system. An analysis of anisotropy revealed that transverse TA2 waves exhibited the highest values for the A coefficient, accounting for 35-43% in the (100) plane and 28-40% in the (001) plane. In contrast, for LA waves, the propagation velocity was nearly isotropic (A parameter close to zero). [ABSTRACT FROM AUTHOR] |
