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中文摘要：
采用基于密度泛函理论的第一性原理研究了在氮氢混合气氛中退火后Bi4Ti3O12铁电性的退化机理.分别计算了无氢、含氢模型中Ti沿c轴位移时体系总能量的变化,电子云密度分布,以及电子结构的总能态密度的变化.结果表明含氢Bi4Ti3O12铁电相Ti-O,Bi-O间的电子云重叠布居分布较无氢情况下变化明显,氢氧之间较强的轨道杂化使它们趋于形成共价键;晶格中氢氧键的钉扎效应使含氢情况下顺电相能量低于铁电相能量,表明氢的引入阻碍了Bi4Ti3O12从四方顺电相到正交铁电相的相变,同时造成Bi4Ti3O12晶体的导电性能增强,并推断其为含氢气氛退火过程中Bi4Ti3O12铁电性能退化的主要原因.
英文摘要：
Degradation of Bi4Ti3O12 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 Bi4Ti3O12 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 Bi4Ti3O12 from tetragonal paraelectricity to orthogonal ferroelectricity,and electrical conductivity of Bi4Ti3O12 is increased.This may be an important factor causing severe degradation of Bi4Ti3O12 ferroelectricity.
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