Effect of interstitial hydrogen on structural and electronic properties of BaTiO3

We investigate the geometry and electronic structure of an interstitial H atom in the BaTiO3 crystal considering both cubic and tetragonal crystallographic lattices. A quantum-chemical method based on the Hartree-Fock formalism is used throughout the study. Interstitial H is found to bind to one of the O atoms, forming the so-called OH group. At equilibrium, the O-H distances are found to be 0.89 and 0.91 Å for cubic and tetragonal lattices respectively. The performed automated geometry optimization procedure of the defective region shows considerable outward movements of atoms closest to the impurity. The role of the H impurity in ferroelectric polarization in the BaTiO3 crystal is analysed using the results obtained in connection with the available experimental data on ferroelectric perovskites.