Phase transitions in metal halide perovskites triggered by external provocations produce significantly different material properties, providing a prodigious opportunity for a comprehensive applications. In the present study, the first principles calculation has been performed with the help of density functional theory (DFT) using CASTEP code to investigate the physical properties of lead-free CsSnBr3 metal halide under various hydrostatic pressures. The pressure effect is determined in the range of 0-16 GPa. Subsequently, a significant change is observed in lattice constant and volume with increasing pressure. The electronic band structure show semiconductor to metal phase transition under elevated pressure. The investigation of optical functions displays that the absorption edge of CsSnBr3 perovskite is shifted remarkably toward the low energy region (red shift) with improved pressure up to 16 GPa. In addition, the absorptivity and dielectric constant also upsurges with the applied hydrostatic pressure. Finally, the mechanical properties reveal that CsSnBr3 perovskite is mechanically stable and highly ductile; the ductility is increased with raising pressure. This type of semiconductor to metal phase transition may inspire a wide range of potential applications. Graphical diagram FIG. 1. A pristine cubic crystal structure of CsSnBr3 perovskite compound

Nano-ripple formation from ultrashort laser pulse irradiation of semiconductors of different band gaps has been studied using a Ti-sapphire laser with 8 mJ energy, 45 fs pulse duration and 800 nm wavelength (1.5eV) at a fluence in the range of ∼100 mJ/cm2 −1J/cm2. The effects of the number of laser shots, angle of incidence, laser polarization, fluence, incident laser wavelength, bandgap, and ambient medium on the ripple period, have been studied. Depending upon the experimental parameters nano-ripple sizes varied in the range of λ-λ/9. The studies clearly show that narrower nano-ripples are formed from wide bandgap semiconductors. In addition, the width of the nano-ripples decreases with the laser wavelength and fluence. The observed results are explained considering the transient metallic nature of the semiconductor surface on irradiation with intense femtosecond pulse which excites surface plasmon leading to the nano-ripple formation. The critical role of the surface plasma electron density in deciding ripple period is identified which helps in generation of narrow sub-wavelength nano-ripples.

Mercury fluoro-perovskites based on Rubidium have a lot of technical relevance nowadays, especially in optical and semiconductive applications. A Cambridge Serial Total Energy Package code analysis using the Density Functional Theory was performed to calculate the structural, electronic, elastic, optical, and thermodynamic characteristics as well as the bonding nature of cubic fluoro-perovskites RbHgF3 under various hydrostatic pressures. To determine the total energy, the Perdew–Berke–Ernzerhof generalized gradient approximation was used to manage the exchange–correlation potential. The effects of hydrostatic pressure are studied in the region of 0–20 GPa, which maintains the cubic stable condition of RbHgF3 fluoro-perovskite. Experimental and prior theoretical results agree well with the calculated lattice parameters. When the pressure reached 20 GPa from 0 GPa, the volume, bond length, and lattice constant decreased. The bandgaps demonstrate an indirect band structure, with substantial reductions at various external forces. The total density of states reveals a non-metallic behavior. Mechanical properties satisfy the stability criteria until 20 GPa for this compound, and ductile behavior is also found within that pressure range. External stress modifies the optical characteristics a bit such as the complicated dielectric function, absorption, conductivity, and reflectivity. The presence of blue shift is confirmed by the movement of absorption edges toward higher energies, making this material an intriguing option for optical devices.

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