First principles study of ferroelectric hexagonal compounds RInO (R = Dy, Er, and Ho): electronic structure, optical and dielectric properties.

The 4f-shell electrons of rare-earth ion R have a certain influence on both the electrical and optical properties of RInO. We have studied the electronic structures, optical and dielectric properties of hexagonal compounds RInO (R = Dy, Ho, and Er) by performing first principles calculations. After optimization, the lattice parameters are in great agreement with the experiment with an error within 1%. Band structure calculations reveal decreasing band gaps with the increase of atomic number, yielding the highest conductivity for ErInO, which has the smallest band gap in the present study. We have calculated the density of states of RInO and characterized the displacement of In and O. The dielectric properties and ionic contribution have been calculated and a detailed comparison has been made on the dielectric function including the static dielectric tensor. The absorption coefficient, the reflectivity, the refractive index, the conductivity and the electron energy-loss spectrum of hexagonal DyInO, HoInO and DyInO have been calculated and analyzed.