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Epitaxial strain is a powerful tool to induce functional properties such as ferroelectricity in thin films of materials that do not possess ferroelectricity in bulk form. In this work, a ferroelectric state was stabilized in thin films of the incipient ferroelectric, CaTiO3, through the careful control of the biaxial strain state and TiO6 octahedral rotations. Detailed structural characterization was carried out by synchrotron x-ray diffraction and scanning transmission electron microscopy. CaTiO3 films grown on La0.18Sr0.82Al0.59Ta0.41O3 (LSAT) and NdGaO3 (NGO) substrates experienced a 1.1% biaxial strain state but differed in their octahedral tilt structures. A suppression of the out-of-plane rotations of the TiO6 octahedral in films grown on LSAT substrates resulted in a robust ferroelectric I4?mm phase with remnant polarization ∼5?μC/cm2 at 10?K and Tc near 140?K. In contrast, films grown on NGO substrates with significant octahedral tilting showed reduced polarization and Tc. These results highlight the key role played by symmetry in controlling the ferroelectric properties of perovskite oxide thin films.

Polymer blends are regarded as a straightforward and effective method to enhance the energy storage performance of dielectric film capacitors. However, how the components and structures within the blend systems affect the energy density and efficiency remains insufficiently explored in-depth. In this discourse, employing a polymer blend of ferroelectric and linear dielectric phases as a paradigm, we perform phase-field simulations to elucidate the effects of ferroelectric phase volume fractions, geometrical dimensions, and the dielectric constant of the linear phase on the energy storage capabilities. Concurrently, we have devised six divergent blending microstructures to probe the ramifications of structural variances on the overarching performance metrics. We also analyze the domain configurations and switching dynamics under varying electric fields to understand the performance variations and delineate the determinants conducive to superior energy density and efficiency. This paper theoretically establishes the component–content–structure–performance relationships of different polymer blend systems, which is expected to better guide the innovative design of new polymer blend dielectrics. [ABSTRACT FROM AUTHOR]

The (PbTiO3)n/(SrTiO3)n (PTO/STO) superlattice system has been shown to exhibit interesting topological phases (e.g., vortices and skyrmions) in addition to normal ferroelectric domain states. Existing studies are mostly focused on the dependence of topological polar distributions and properties of PTO/STO superlattice on its periodicity. Here, we study the strain effect on the topological phase transitions and ferroelectric domain structures employing phase-field simulations. We summarized in an isotropic strain (in-plane misfit strain along the x direction is equal to that along the y direction) periodicity phase diagram displaying the stability regions of different polar topological states, including normal ferroelectric twins, vortices, skyrmions, and mixtures of vortices and twins. We also analyzed the polarization configurations under anisotropic in-plane strains (in-plane misfit strain along the x direction is not equal to that along the y direction) and demonstrated that the strain anisotropy can be used to tune the directions of vortex arrays along either the [100] pc or [010] pc directions or labyrinth vortex arrays. This work offers guidance to manipulating polar structures in the PTO/STO superlattices via strain engineering. [ABSTRACT FROM AUTHOR]

Potassium-sodium niobate K1-xNaxNbO3 (KNN) is one of the most promising lead-free piezoelectric materials. While there have been many studies on the microstructures and properties of KNN ceramics, the phase transitions and ferroelectric domain structures of KNN thin films are not well understood. In this work, we employ three-dimensional (3D) phase-field simulations to obtain the ferroelectric domain structures of KNN (0 ≤ x ≤ 0.5) thin films under a range of temperatures (0 K to 1300 K) and equiaxial misfit strains (–1.5% to 1.5%), based on which we establish the misfit strain-temperature phase diagrams of KNbO3 and K0.5Na0.5NbO3 thin films. We identify a wide variety of complex domain structures with coexisting ferroelectric phases, implying enhanced dielectric and piezoelectric properties. We expect this work to provide guidance for the strain engineering of domain structures and properties of KNN thin films. [ABSTRACT FROM AUTHOR]

It has been known that ferroelectric charged domain walls (CDWs), which break the polarization continuity, may be electrically active with an elevated conductivity. However, the bound charge at CDWs may render them energetically unstable, and thus, forming CDWs naturally and manipulating them electrically is still challenging. Here, we theoretically utilize phase-field simulations to design spontaneously generated CDWs with center-type quad-domains in a single square-shaped BiFeO3 nanoisland. It is shown that the stability of the spontaneously emerging head-to-head domain walls with center-convergent quad-domains is mainly determined by three contributions, namely, the geometrical constraint from approximately 45°-tilted bottom edges, the electric boundary condition, and the necessary screening free charges to compensate head-to-head domain walls. It is demonstrated that the center-convergent quad-domains with head-to-head CDWs can be electrically switched to the center-divergent one with tail-to-tail CDWs, providing guidance for achieving ferroelectric domain-wall-based nanodevices with low-power dissipation. [ABSTRACT FROM AUTHOR]

The issue of imaginary phonon modes predicted by first-principles calculations for high-temperature structures of most materials has been a longstanding problem for decades. We propose that the observed high-temperature structures are actually dynamic averages of related low-temperature structures. This theory is used to predict the phonon dispersions of cubic SrTiO3. The calculated phonon dispersions for the cubic phase, using the force constants calculated from the tetragonal phases, are found to be in remarkably good agreement with existing neutron data, without exhibiting any imaginary phonon modes. [ABSTRACT FROM AUTHOR]

A correction to the article "Polarization rotation transitions in anisotropically strained SrTiO3 thin films," that was published in the 2008 issue is presented.

The issue of imaginary phonon modes predicted by first-principles calculations for high-temperature structures of most materials has been a longstanding problem for decades. We propose that the observed high-temperature structures are actually dynamic averages of related low-temperature structures. This theory is used to predict the phonon dispersions of cubic SrTiO3. The calculated phonon dispersions for the cubic phase, using the force constants calculated from the tetragonal phases, are found to be in remarkably good agreement with existing neutron data, without exhibiting any imaginary phonon modes. [ABSTRACT FROM AUTHOR]