Structure, electronic, optical and elastic properties of (NH4)2BeF4 crystal in paraelectric phase

Abstract

The theoretical study of the structure and specific properties of the (NH4)2BeF4 crystal is carried out within the framework of the DFT. The band-energy structure of the (NH4)2BeF4 crystal in paraelectric phase is calculated and discussed. The edge of the fundamental absorption of the crystal is assumed to be associated with direct transitions in the center of Brillouin zone. The real and imaginary parts of the dielectric function as well as spectral dependence of the principal refractive indices of the crystal are calculated. Experimental study of the refractive indices dispersions of the grown crystal is carried out; the calculated dependances reveal good agreement with experimental data. Theoretical elastic coefficients Сij are calculated. The anisotropy of optical and elastic properties, which is important for possible applications, has been highlighted by means of the 2D and 3D graphs. The presented results should be very useful for future anisotropy-based implementations of the crystal.