IMF2017

Ferroelectric materials are critical components in a wide range of devices such as non-volatile memories, actuators, sensors, and electro-optic devices. For the practical applications in recent trend of miniaturization, it is essential to understand and enhance ferroelectricity of thin films including piezoelectricity and polarization switching. Recently, special attention has been given to ferroelectric materials due to the presence of morphotropic phase boundaries (MPB), or strain driven mixed phases of ferroelectric domain that enhanced electromechanical property. In the ferroelectric BiFeO­₃ (BFO) thin films, for example, the film tends to form rhombohedral phase in the middle of tetragonal phase in order to relieve the stress from substrate. The existence of rhombohedral phase has been well predicted to enhance electromechanical properties of BFO thin films arising from the large lattice distortion under an applied electric field; however, its dynamic phenomena has not been clearly investigated yet partially due to the lack of experimental tools. Recently, time resolved micro X-ray diffraction under electric field allow us to resolve not only structural change but also electromechanical properties of thin films. Change of diffracted intensity and shift of diffracted peak position under electric field will provide information on ferroelectric switching and piezoelectric response, respectively. As results, we found nonlinear phase transition between simple cubic and super tetragonal structures. The simple cubic structure showed ferroelectric switching under electric field while super tetragonal only showed linear piezoelectric response indicating the origin of phase transition.