KNbO_3 180°畴的第一性原理计算

First-Principles Calculation on 180° Domain of KNbO3

利用第一性原理计算方法,考察铁电材料KNbO3的180°畴结构,并计算以K和Nb原子为对称中心的畴壁厚度、畴壁能及两种畴壁间移动的势垒高度.结果表明：该材料的畴壁厚度为1～2个晶胞常数;以K原子为对称中心的畴壁更稳定,其畴壁能为7.58 mJ/m^2;以Nb为对称中心的畴壁不稳定,会逐渐变为以K为对称中心的畴壁,其畴壁能为15.16mJ/m^2;畴壁移至最近邻晶格位置的势垒值为7.58mJ/m^2.

Using the first-principles calculation,we studied the 180° domain in the ferroelectric material of KNbO3 and calculated the thickness,energy and barrier height for the coherent motion of the domain wall of both K centered and Nb centered domain walls.Our calculation reveals that the thickness of 180° domain wall is only one to two lattice constants.The K centered domain wall is preferred because its formation energy（7.58mJ/m^2）is half of that of the Nb centered domain wall（15.16mJ/m^2）.The Nb centered domain wall is unstable and will gradually change to the K centered domain wall.The barrier height for the coherent motion of the domain wall to its neighboring lattice position is 7.58mJ/m^2.