The effect of pressure on the structural, optoelectronic and mechanical conduct of the <i>X</i>ZnF₃ (X= Na, K and Rb) perovskite: First-principles study

Abstract

By using the DFT approach within the generalized gradient approximation (GGA) adopted in the Wien2k code, the effects of pressure on the structural, electrical and optical characteristics of XZnF 3 ([Formula: see text] Na, K and Rb) halide perovskites have been investigated. In the present paper, the unit cell structures of XZnF 3 ([Formula: see text] Na, K and Rb) have been optimized. Within the present approximation, the analysis showed indirect bandgaps of those compounds. At 0[Formula: see text]GPa, the density of states (DOS) besides band structures predicted the bandgaps of (2.80, 3.84 and 4.22[Formula: see text]eV) connected to (NaZnF 3 , KZnF 3 and RbZnF[Formula: see text], respectively. These indirect bandgaps increase from (0 to 20[Formula: see text]GPa) with hydrostatic pressure. Regarding the optical properties, the imaginary part [Formula: see text] of the dielectric function, the absorption [Formula: see text], the reflectivity [Formula: see text] and the refractive index [Formula: see text] are determined. The light absorption at the surface begins at critical points corresponding to the threshold energy, their values of (5.00, 5.20 and 5.30[Formula: see text]eV at 0[Formula: see text]GPa) and (5.90, 6.30 and 6.50[Formula: see text]eV at 20[Formula: see text]GPa) related to NaZnF 3 , KZnF 3 and RbZnF 3 , respectively. The pressure induced in XZnF 3 ([Formula: see text] Na, K and Rb) reduces absorption intensity to a remarkable extent, both in the visible and ultraviolet range and the intensity of the reflectivity spectra decreases with increasing pressure. When there is no induced pressure, optical conductivity starts out with lower photon energies and increases as pressure builds up, reaching greater photon energies at pressures of up to 20[Formula: see text]GPa. The mechanical stability of the material studied is verified using the Born stability criteria, the values obtained for the elastic constants verify the stability conditions of XZnF[Formula: see text] Na, K and Rb), improving with applied pressure 0 up to 20[Formula: see text]GPa. NaZnF 3 and KZnF 3 have slightly higher ductility than RbZnF 3 at 0[Formula: see text]GPa, and KZnF 3 has a slightly higher ductility than NaZnF 3 at 0[Formula: see text]GPa, and higher than RbZnF 3 at 20[Formula: see text]GPa. Also, the mechanical stability is verified using the Born stability criteria, where the elastic constants verify the stability conditions. The Cauchy pressure value of XZnF 3 ([Formula: see text] Na, K and Rb) perovskite under all the pressures studied is positive, indicating that the ductile nature of perovskite improves and increases with increasing pressure.