Abstract
Because the functions of polar materials are governed primarily by their polarization response to external stimuli, the majority of studies have focused on controlling polar lattice distortions. In some perovskite oxides, polar distortions coexist with nonpolar tilts and rotations of oxygen octahedra. The interplay between nonpolar and polar instabilities appears to play a crucial role, raising the question of how to design materials by exploiting their coupling. Here, we introduce the concept of ‘polarization twist’, which offers enhanced control over piezoelectric responses in polar materials. Our experimental and theoretical studies provide direct evidence that a ferrielectric perovskite exhibits a large piezoelectric response because of extended polar distortion, accompanied by nonpolar octahedral rotations, as if twisted polarization relaxes under electric fields. The concept underlying the polarization twist opens new possibilities for developing alternative materials in bulk and thin-film forms.
Highlights
Structural diversity of perovskite oxides offers exciting opportunities for exploring the functions of dielectrics[1], ferroelectrics[2] and multiferroics[3,4]
In situ X-ray diffraction (XRD) analysis using high-energy synchrotron radiation demonstrates that electric fields induce an extended polar displacement associated with nonpolar octahedral rotations in ferrielectric crystals, as if twisted polarization relaxes and stretches
Our simulations based on density functional theory (DFT) and phenomenological theory show that this concept stems from a structural coupling between nonpolar octahedral rotation and polar distortion
Summary
Structural diversity of perovskite oxides offers exciting opportunities for exploring the functions of dielectrics[1], ferroelectrics[2] and multiferroics[3,4]. Detailed structural analyses and theoretical calculations of lead-based ferroelectrics have revealed that the Ps vector rotates under electric fields, inducing a large piezoelectric response[11,12,13,14,15]. A nonpolar octahedral rotation with a double-well energy potential that constitutes the primary order parameter causes a ferroelectric polarization with a single-well potential[16,17]. This nonpolar rotation strongly affects the electrical properties[18]. In situ X-ray diffraction (XRD) analysis using high-energy synchrotron radiation demonstrates that electric fields induce an extended polar displacement associated with nonpolar octahedral rotations in ferrielectric crystals, as if twisted polarization relaxes and stretches. Our simulations based on density functional theory (DFT) and phenomenological theory show that this concept stems from a structural coupling between nonpolar octahedral rotation and polar distortion
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