Effect of hydrogen on ferroelectric properties of Bi 4 Ti 3 O 12 during forming gas annealing

Degradation of Bi 4 Ti 3 O 12 ferroelectricity during forming gas annealing is investigated by the first-principles method based on the density functional theory(DFT) the generalized gradient approximation(GGA). We calculate the variations of total energy with the displacement of Ti along the c axis, electron density and total density of states in hydrogen-free and hydrogenated models. The results show that the electron densities of Ti-O and Bi-O exhibit significant changes between the Bi 4 Ti 3 O 12 ferroelectric phases for the hydrogenated and hydrogen-free cases, and the strong hybridization between H and O is favorable to the formation of a convalent bond. The total energy of ferroelectric phase for the hydrogenated case is bigger than that of paraelectric phase because hydrogen incorporation into the lattice has a direct effect on polarization pinning by possibly forming a hydroxyl bond. This demonstrates that hydrogen introduction during forming gas annealing hinders the phase transition of the Bi 4 Ti 3 O 12 from tetragonal paraelectricity to orthogonal ferroelectricity, and electrical conductivity of Bi 4 Ti 3 O 12 is increased. This may be an important factor causing severe degradation of Bi 4 Ti 3 O 12 ferroelectricity.