npj Computational Materials

Strain engineering of electro-optic constants in ferroelectric materials (铁电材料电-光常数的应变工程)
Charles Paillard, Sergei Prokhorenko & Laurent Bellaiche
npj Computational Materials 5:6 (2019)
doi:s41524-018-0141-4
Published online:08 January 2019
Abstract| Full Text | PDF OPEN

摘要:基于电-光效应可以利用电场调控光强变化成为可能，该效应对于当今信息和通信技术（例如电视显示器和光纤）十分重要。在薄膜中寻找大的电-光常数对于电-光器件的小型化和提高电-光效率十分关键。本研究证明了通过PbTiO₃ 薄膜的应变工程可以有选择性地改进某个电-光常数。我们预测了高达100pmV^-1 的无应力电光常数，该数值既可以源于拉伸应变作用下相变边界处光学声子模式的软化，亦可源于压缩应变产生等效负压导致的大压电常数。具体地，可以通过在硅这一技术上十分重要的衬底材料上生长出PbTiO₃，来获得大的r₃₃电-光系数，其数值可为常用的LiNbO₃ 电光材料的两倍。　　

Abstract:Electro-optic effects allow control of the ow of light using electric fields, and are of utmost importance for today’s information and communication technologies, such as TV displays and fiber optics. The search for large electro-optic constants in films is essential to the miniaturization and increased efficiency of electro-optic devices. In this work, we demonstrate that strain-engineering in PbTiO₃ films allows to selectively choose which electro-optic constant to improve. Unclamped electro-optic constants larger than 100pmV^-1 are predicted, either by driving the softening of an optical phonon mode at a phase transition boundary under tensile strain, or by generating the equivalent of a negative pressure via compressive strain to obtain extremely large piezoelectric constants. In particular, a r₃₃ electro-optic coefficient twice as large as the one of the commonly used LiNbO₃ electro-optic material is found here when growing PbTiO₃ on the technologically important Si substrate.

Editorial Summary

Large electric-optic constant: Strain engineering in PbTiO₃film

基于铁电薄膜PbTiO₃ 的应变工程（拉伸或压缩）即可选择性地获得大的电-光常数。在薄膜中寻找大电-光常数对于电-光器件的小型化和提高电-光效率是必不可少的。来自美国阿肯色大学的LaurentBellaiche 领导的团队，采用精确的从头算技术，研究了应变对于PbTiO₃这一经典铁电体电-光特性的影响，以企确定导致铁电PbTiO₃薄膜中高电光性能的一般机制。计算结果显示，应变工程可以有选择性地改进某个电-光常数，具体增强机制有两种：其一为利用拉伸应变实现相变边界处光学声子模式的软化；其二为利用压缩应变产生等效负压导致大的压电系数。他们通过计算预测出了应变下的大于100pmV^-1 的大电-光常数, 发现若以硅材料作生长PbTiO₃薄膜的衬底，所获得的薄膜材料的r₃₃电-光系数可达57 pm/V，接近标准电-光材料LiNbO₃的两倍！

Large electric-optic constant can be obtained by strain engineering in ferroelectric film. Films with large electro-optic (EO) constants is essential for miniaturization of EO devices and improving EO efficiency. A team led by Laurent Bellaiche from the University of Arkansas in the United States, using precise ab initio techniques, explored a wide range of epitaxial strain conditions to determine EO effects in ferroelectric PbTiO₃ films. They demonstrated that strain engineering of PbTiO₃ films can be arbitrarily chosen to improve a certain EO constant. Two enhancing mechanisms were found, as the first driven force is softening of an optical phonon mode at a phase transition boundary under tensile strain, while the other is driven by the extremely large piezoelectric constants resulted from generating the equivalent of a negative pressure via compressive strain. EO constants larger than 100pmV^-1 were predicted, and could attain 57 pm/V, almost twice the standard electro-optical material LiNbO₃ if PbTiO₃ film growing on the technologically important Si substrate.