Uniaxial strain-induced ferroelectric phase with a giant axial ratio in a (110) BiFeO3 thin film

Abstract

Strain engineering, which employs biaxial misfit strain to deform the crystal structure, is a powerful tool to tune the physical behavior of epitaxial thin films. Here we show that a 10-nm-thick BiFeO3 film is uniaxially strained by (110)-oriented LaAlO3 substrate, which exhibits a monoclinic lattice with a giant c/a ∼ 1.24 and a unique stripe ferroelectric domain configuration, as revealed by high resolution synchrotron x-ray diffraction and piezoelectric force microscopy. A strain-phase diagram for BiFeO3 under uniaxial strain condition is predicted by first-principles calculations, suggesting that monoclinic Pm phase with a large polarization of ∼130 μC/cm2 is the lowest-in-energy phase when strained by (110)-oriented LaAlO3 substrate. Our results provide a potential route to tune physical behavior of epitaxial ferroelectric thin films by uniaxial strain in (110) orientation, instead of widely investigated biaxial strain in (001) orientation. © 2013 American Physical Society.