Pressure Effect of the Vibrational and Thermodynamic Properties of Chalcopyrite-Type Compound AgGaS₂: A First-Principles Investigation.

Jianhui Yang,Qiang Fan,You Yu,Weibin Zhang

doi:10.3390/ma11122370

Jianhui Yang, Qiang Fan + Show 2 more

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https://doi.org/10.3390/ma11122370

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Abstract

To explore the structural, vibrational, and thermodynamic properties of the chalcopyrite-type compound AgGaS2 under pressure, we applied hydrostatic pressure to the relaxed compound based on the first principles calculation and quasi-harmonic approximation. The structural parameters, including lattice constants and bond lengths decrease monotonically with the increasing pressure. The phonon dispersion curves under various pressures reveal the structural phase transition of chalcopyrite-type compound AgGaS2 at about 4 GPa. The intrinsic mechanism of thermal conductivity for the chalcopyrite-type compound AgGaS2 has been shown with phonon anharmonicity. The frequencies of the optical phonons at the center point Γ of the first Brillouin zone were calculated with the longitudinal optical–transverse optical (LO–TO) splitting mode. The dependence of the frequencies of the optical phonons on the pressure provides the information for the Raman spectroscopic study under high pressure. The pressure dependence of the Grüneisen parameters indicates that the instability of chalcopyrite-type compound AgGaS2 is associated with the softening of the acoustic phonon modes at around the center point Γ. The thermal conductivity for chalcopyrite-type compound AgGaS2 could be reduced by applying external pressure. The various thermodynamic properties, such as the Helmholtz free energy, entropy, and heat capacity, at different temperatures and pressures were discussed and analyzed based on the phonon properties.

Highlights

I-III-VI2 ternary chalcopyrite type compounds have attracted attention as extracting candidates in non-linear optic [1,2,3], novel spintronic [4], and thermoelectric [5,6,7] devices, as well as in thin film solar cells [8,9,10]
AgGaS2 under different hydrostatic pressures were investigated by using the first-principles calculation and quasi-harmonic approximation
The lattice constants and bond lengths were observed to decrease with increasing pressure, which leads to a higher phonon frequency of the optical branches

Summary

Introduction

I-III-VI2 ternary chalcopyrite type compounds have attracted attention as extracting candidates in non-linear optic [1,2,3], novel spintronic [4], and thermoelectric [5,6,7] devices, as well as in thin film solar cells [8,9,10]. AgGaS2 , as a typical member of I-III-VI2 ternary chalcopyrite-type compounds, has attracted interest from researchers [11,12,13]. Holah et al presented the lattice dynamic properties of chalcopyrite-type compound AgGaS2 in an experiment for the first time in 1974 [15]. The lattice dynamic and thermodynamic properties of the chalcopyrite-type compound AgGaS2 have attracted the attention of theoretical researchers for its potential application. Wei et al investigated the anharmonicity of the acoustic phonon of AgGaS2 using first principles under the three-phonon Umklapp process [18]

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