氢对PbZr_(0.5)Ti_(0.5)O_3在氮氢混合气氛退火中铁电性能的影响

Effect of Hydrogen on the Ferroelectric Properties of PbZr_(0.5)Ti_(0.5)O_3 during Forming Gas Annealing

采用基于密度泛函理论的第一性原理,针对PbZr0.5Ti0.5O3无氢和含氢的顺电相和铁电相的二层超晶胞,分别计算了Ti沿c轴位移时体系总能量的变化、电子云密度分布和Ti—O、Zr—O和H—O的重叠布居数.结果表明,含氢铁电相的Ti—O键和Zr—O键相对无氢铁电相明显减弱,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的顺电相能量始终低于铁电相能量,说明氢的引入阻碍了PbZr0.5Ti0.5O3从立方顺电相到四方铁电相的相变,并推断其为含氢气氛退火过程中PbZr0.5Ti0.5O3铁电性能下降的主要原因之一.所得结果对于深入理解铁电材料在氮氢混合气氛退火后铁电性能下降的微观机制具有参考价值.

Ferroelectric and paraelectric states of two-layer supercell PbZr0.5Ti0.5O3 for hydrogen-free and hydrogenated were investigated using first principles density functional theory. We calculated the variation of the total energy with the displacement of Ti along the c axis, the density of states and the Mulliken population between Ti--O, Zr--O and H--O bonds. The results show that the Ti--O and Zr-O bonds of the ferroelectric phase for the hydrogenfree are stronger than those for the hydrogenated and that the strong hybridization between H and O is favorable to form covalent bond between the two atoms. The total energy of the ferroelectric phase for the hydrogenated is higher than that of the paraelectric phase because hydrogen incorporation into the lattice has a direct effect on polarization pinning by possibly forming hydroxyl bond. These data demonstrate that hydrogen introduction during forming gas annealing, hindering phase transition of the PbZrosTiosOa from cubic paraelectric to tetragonal ferroelectric phase, is an important factor causing severe degradation of ferroelectricity in PbZr0.5Ti0.5O3. This study may be helpful to understand the mechanism of severe ferroelectricity degradation for ferroelectric materials during forming gas annealing.