压力作用下KNbO_(3)相变行为的分子动力学研究

Molecular Dynamics Study of the Phase Transition Behavior of KNbO_(3)Under Pressure

【目的】研究铁电材料KNbO_(3)在压力作用下的相变行为,分析尺寸效应和电场对KNbO_(3)相变压力的影响,为KNbO_(3)结构和性能的调控提供指导。【方法】基于核壳模型的分子动力学方法,研究KNbO_(3)极化强度和晶格参数随压力的演变行为,分析获得了KNbO_(3)的三个相变压力;研究不同尺寸下KNbO_(3)的相变行为,分析了尺寸效应对相变压力的影响;通过在KNbO_(3)的相变过程中施加电场,分析了电场对相变压力的影响。【结果】研究表明,KNbO_(3)的相变压力依次为2.28 GPa、5.32 GPa和6.61 GPa;当KNbO_(3)体系的原子总数超过60000时,获得的相变压力值是相对稳定的;电场—压力相图表明在电场的作用下相变压力会发生偏移。【结论】相变压力具有非常显著的尺寸效应,电场的大小和方向对KNbO_(3)结构和性能的调控具有重要的指导意义。

[Purposes]The phase transition behavior of the ferroelectric material KNbO_(3)under pressure is investigated,and the effects of size effect and electric field on the phase transition pressure of KNbO_(3)are analyzed to guide the regulation of KNbO_(3)structure and properties.[Methods]Based on the molecular dynamics method of the core-shell model,the evolution behaviors of KNbO_(3)polarization intensity and lattice parameters with pressure are investigated,and the three-phase transition pressures of KNbO_(3)are analytically obtained;the phase transition behaviors of KNbO_(3)under different sizes are investigated,and the effect of size effect on the phase transition pressure is analyzed;the effect of electric field on the phase transition pressure is analyzed by applying electric field during the phase transition of KNbO_(3).[Findings]The study showed that the phase transition pressures of KNbO_(3)are 2.28 GPa,5.32 GPa and 6.61 GPa respectively;the obtained phase transition pressure values are relatively stable when the total number of atoms of the KNbO_(3)system exceeds 60000;the electric fields-pressure phase diagram indi⁃cates that the phase transition pressure is shifted under the effect of electric fields.[Conclusions]The phase transition pressure has a very significant size effect,and the magnitude and direction of the elec⁃tric field are an important guide to the regulation of KNbO_(3)structure and properties.