First-principles Study Of The Structure And Polarization Of Barium Titanate

Ferroelectric materials,as an important functional materials, attracted researchers all over the world, due to its excellent ferroelectric, piezoelectric, thermoelectric andnonlinear optical properties. And the spontaneous polarization, as an important representative of ferroelectric properties, is the main object to study, In this paper, we uesd first-principles method based on density functional theory to study the structure and polarization characteristics of the barium titanate.Firstly, we use first-principles methods to optimize the structure of cubic and tetragonal BTO. The calculated lattice of the cubic phase is4.010,and the average lattice of tetragonal phase is4.004.Both experimental error if below the0.5%.Then we analysis the electric properties of both phases, The results shows that:there are Ti3d electrons and O2p electron orbital hybridization in both ferroelectric and cubic phase, according to the density of statesand, band structure, the degree of hybridization in ferroelectric phase is significantly higher than the paraelectric phase. And with the ferroelectric phase transition occurs, the degree of hybridization between Ti-O track enhances, the the total energy of system reduces, thus ensuring the stability of the ferroelectric phase at room temperature.Then we built some models by changing the Ti atoms’position along the z axis to stimulate how the BTO change in electric field. After the geometry optimization,we use first-principles calculate how the displacement of Ti atoms in Ti-O octahedral influence the polarization characteristics and atoms structure.When the Ti atoms moves along the z-axis0.02,BTO is still cubic phase,but the orbital hybridization degree is stronger than the original cubic phase.With eccentric displacement increases, oxygen octahedral distortion, and the structure turns to ferroelectric phase. Then we calculated the electronic structure of optimized BTO crystals. With eccentric displacement increases, the bond between Ti and O Ⅰ turn to ionic, and the hybrid effect between Ti and OⅡ become stronger.Band structure shows that the band gap decreases with the eccentricdisplacement increases, which may lead to the disappearance of the forbidden band.