Highly anisotropic layered crystal AgBiP2Se6: Growth, electronic band-structure and optical properties

A centimeter size crystal of silver- and bismuth-bearing selenophosphate, AgBiP2Se6, was effectively grown for the first time by Bridgman technique and characterized via different experimental and theoretical techniques to explore its quality and some physicochemical properties. The present experimental and theoretical data reveal a well-defined layered structure of the AgBiP2Se6 compound and its highly anisotropic optical constants. In particular, the AgBiP2Se6 crystal was studied to estimate binding energies of core-level electrons of the atoms constituting the crystal and to explore the energy distribution of the valence electronic states for both as-grown and treated with middle-energy Ar+ ions surfaces. The XPS data reveal high hygroscopicity of the AgBiP2Se6 crystal. The SEM/EDX results feature a composition of the crystal to be very close to a nominal stoichiometric content. In the present work we probe various models to gain the best correspondence of theoretical total density of states curve and the experimental XPS spectrum. We have established theoretically that contributions of Se p states prevail in the upper section of the valence band, its central section is prevailed by Ag d states, while the bottom is formed from contributions of P p states. Following the band-structure findings, we examine in detail the optical constants of the compound under study. In particular, the present calculations yield that AgBiP2Se6 is a promising optoelectronic semiconductor with essential anisotropic behavior for two main non-zero diagonal constituents of the second order dielectric tensor in special energy regions for all the optical constants, whereas the energy-loss spectrum is isotropic.

Automated summary

In this study, a centimeter size crystal of silver- and bismuth-bearing selenophosphate, AgBiP2Se6, was grown for the first time by Bridgman technique and characterized via different experimental and theoretical techniques. The AgBiP2Se6 compound was found to have a well-defined layered structure and highly anisotropic optical constants, making it a promising optoelectronic semiconductor. Theoretical analysis revealed the dominance of Se p states in the upper section of the valence band, Ag d states in the central section, and P p states in the bottom section.