Investigation of the physical properties and pressure-induced band gap tuning of Sr3ZBr3 (Z=As, Sb) for optoelectronic and thermoelectric applications: A DFT - GGA and mBJ studies

Abstract

• Sr 3 AsBr 3 and Sr 3 SbBr 3 both are direct band gap semiconductors. • The study validates the dynamic stability of lead-free Sr 3 ZBr 3 (Z = As, Sb) through phonon dispersion spectra analysis, showing no negative frequencies. • Pressure enhances optical properties, increasing spectral response and photon sensitivity. • High pressure induces a brittle to ductile transition, improving ductility and anisotropy. • Sr 3 ZBr 3 (B = As, Sb) compounds are mechanically and thermodynamically stable with enhanced ductility and machinability under pressure. This study discusses the feasibility of diversifying the scope of application of lead-free Sr 3 ZBr 3 (Z = As, Sb) as promising materials for their enhanced electronic, mechanical, optical, thermodynamic, and thermoelectric properties using first-principles calculation based on Density Functional Theory (DFT). Both compounds have cubic crystal structures, and both materials' dynamic stability is validated by the lack of negative frequencies in their phonon dispersion spectra. Besides ground state physical characteristics, we also examined the impact of hydrostatic pressure (0-21 GPa) on electronic, mechanical, and optical properties. The lattice parameters exhibit a linear decrease from 6.27 to 5.61 Å for Sr 3 AsBr 3 and 6.45 to 5.71 Å for Sr 3 SbBr 3 under increasing pressure, attributed to bond length reduction, which alters their physical properties. Initially observed direct band gap (Γ-Γ) of Sr 3 AsBr 3 and Sr 3 SbBr 3 were 2.35 and 2.30 eV using modified Becke-Johnson (mBJ) functional which reduces to 1.15 and 0.82 eV as the compounds go from 0 to 21 GPa pressure. This study reveals enhanced optical properties under pressure, with broader spectral response, increased sensitivity, and improved dielectric constant. Optical absorption and conductivity also shift toward lower-energy photons. The investigation further shows that the compounds show brittle to ductile transition under high pressure. Their ductility and anisotropy nature are further enhanced with pressure along with other mechanical features. The thermodynamic properties indicate their ability to withstand and perform well at high temperatures and pressures. Lastly, the thermoelectric properties of Sr 3 ZBr 3 (Z = As, Sb) were assessed through electrical and thermal conductivity, Seebeck coefficient, power factor (PF), and figure of merit (ZT) as a function of temperature. Both compounds exhibit high PF and near-unity ZT. These findings underscore their potential as strong candidates for optoelectronic and thermoelectric devices, owing to their direct bandgap and exceptional properties.