Tan Zhi, Peng Yuting, An Jiao, Zhang Qiming, Zhu Jianguo
College of Materials Science and Engineering, Sichuan University, Chengdu 610065, China.
Department of Physics, University of Texas at Arlington, Arlington, Texas 76019, USA.
Inorg Chem. 2021 Jun 7;60(11):7961-7973. doi: 10.1021/acs.inorgchem.1c00478. Epub 2021 May 19.
The evolution of local atomic configuration and macroscopic electrical properties of KNbO is investigated in detail using molecular dynamics simulations within the framework of density functional theory. By analyzing the local off-center displacements of K and Nb atoms, the presence of the crossover of displacive and order-disorder mechanisms in the NbO octahedron due to orbital hybridization is found, whereas the K is a completely displacive type due to the nonoriented ionic K-O bond. Besides, the order-disorder behavior of Nb atoms is enhanced with the increase in temperature, especially undergoing the phase transition. The predicted high dielectric constant of KNbO confirms the key role of the Nb's order-disorder behavior. We discover that the anomalous increase in dielectric constant in the vicinity of the phase boundary is not only from the transformation of the polarized direction but also from the enhancement of order-disorder contribution in the nonpolarized direction. The high dielectric constant with large spontaneous polarization boosts the piezoelectricity at the orthorhombic-tetragonal phase boundary of 500 K, giving rise to the nearly 100% increase than that of 300 K. A rebonding model is developed to illustrate the origin of high piezoelectricity around the tetragonal ferroelectric phase boundary, and the significance of introducing a tetragonal structure is emphasized for developing high piezoelectricity in the inorganic perovskite ferroelectrics.
在密度泛函理论框架内，利用分子动力学模拟详细研究了铌酸钾（KNbO）的局部原子构型和宏观电学性质的演变。通过分析钾（K）和铌（Nb）原子的局部位移，发现由于轨道杂化，在NbO八面体中存在位移和有序-无序机制的交叉，而由于非定向离子K-O键，K是完全位移型。此外，Nb原子的有序-无序行为随温度升高而增强，特别是在发生相变时。预测的KNbO高介电常数证实了Nb有序-无序行为的关键作用。我们发现，相界附近介电常数的异常增加不仅源于极化方向的转变，还源于非极化方向上有序-无序贡献的增强。在500K的正交-四方相界处，具有大自发极化的高介电常数增强了压电性，比300K时增加了近100%。建立了一个再键合模型来说明四方铁电相界周围高压电性的起源，并强调了引入四方结构对于在无机钙钛矿铁电体中开发高压电性的重要性。
