Dielectric capacitors can store and release electric energy at ultrafast rates and are extensively studied for applications in electronics and electric power systems. Among various candidates, thin films based on relaxor ferroelectrics, a special kind of ferroelectric with nanometer-sized domains, have attracted special attention because of their high energy densities and efficiencies. We show that high-energy ion bombardment improves the energy storage performance of relaxor ferroelectric thin films. Intrinsic point defects created by ion bombardment reduce leakage, delay low-field polarization saturation, enhance high-field polarizability, and improve breakdown strength. We demonstrate energy storage densities as high as ~133 joules per cubic centimeter with efficiencies exceeding 75%. Deterministic control of defects by means of postsynthesis processing methods such as ion bombardment can be used to overcome the trade-off between high polarizability and breakdown strength.

Alternatively, molecular-dynamics (MD) simulations have shown that relaxors can be interpreted as exhibiting a multidomain state without a nonpolar matrix (i.e., polar nanodomains or PNDs). [4] The exact nature of order in relaxors, however, remains an ongoing debate [5] and, in turn, new approaches to study these complex materials are required to further illuminate the structure and how it can be controlled and can impact material properties. [5-9] In any case, it is essential to understand the evolution of the polar structure in relaxors (be they PNRs or PNDs) under applied stimuli as these are key to understanding relaxor behavior and large electromechanical effects in relaxors. Over the years, X-ray and neutron diffuse-scattering measurements have emerged as an essential tool to study the structural signatures of relaxor behavior [10-19] and studies on single-crystal relaxors have investigated the evolution of polar regions/domains (e.g., size, morphology) and suggested that they alter their size [14-17] and orientation [18] under different external stimuli. For example, under applied electric fields, which were expected to enhance polar order, the local order was found to align perpendicular to the field [18] and induce an asymmetry in the lattice dynamics [19] that could ultimately be responsible for the large electromechanical effects. [20] Other studies used pressure to push the material in the opposite directionto destabilize polar order [17]-and even induce a crossover from Understanding and ultimately controlling the large electromechanical effects in relaxor ferroelectrics requires intimate knowledge of how the local-polar order evolves under applied stimuli. Here, the biaxial-strain-induced evolution of and correlations between polar structures and properties in epitaxial films of the prototypical relaxor ferroelectric 0.68PbMg 1/3 Nb 2/3 O 3-0.32PbTiO 3 are investigated. X-ray diffuse-scattering studies reveal an evolution from a butterfly-to disc-shaped pattern and an increase in the correlation-length from ≈8 to ≈25 nm with increasing compressive strain. Molecular-dynamics simulations reveal the origin of the changes in the diffuse-scattering patterns and that strain induces polarization rotation and the merging of the polar order. As the magnitude of the strain is increased, relaxor behavior is gradually suppressed but is not fully quenched. Analysis of the dynamic evolution of dipole alignment in the simulations reveals that, while, for most unit-cell chemistries and configurations, strain drives a tendency toward more ferroelectric-like order, there are certain unit cells that become more disordered under strain, resulting in stronger competition between ordered and disordered regions and enhanced overall susceptibilities. Ultimately, this implies that deterministic creation of specific local chemical configurations could be an effective way to enhance relaxor performance.

The ability to tailor a new crystalline structure and associated functionalities with a variety of stimuli is one of the key issues in material design. Developing synthetic routes to functional materials with partially absorbed non-metallic elements (i.e., hydrogen and nitrogen) could open up more possibilities for preparing novel families of electronically active oxide compounds. Here, we introduce a fast and reversible uptake and release of hydrogen in epitaxial ABO3 manganite films through an adapted low-frequency inductively coupled plasma technology. Compared with traditional dopants of metallic cations, the plasma-assisted hydrogen implantations not only produce reversibly structural transformations from pristine perovskite (PV) phase to a newly found protonation-driven brownmillerite (BM) one, but also regulate remarkably different electronic properties driving the material from a ferromagnetic metal to a weakly ferromagnetic insulator for a range of manganite(La1-xSrxMnO3) thin films. Moreover, a reversible perovskite-brownmillerite-perovskite (PV-HBM-PV') transition is achieved at a relatively low temperature (T ≤ 350°C), enabling multi-functional modulations for integrated electronic systems. The fast, low-temperature control of structural and electronic properties by the facile hydrogenation/dehydrogenation treatment substantially widens the space for exploring new possibilities of novel properties in proton-based multifunctional materials.

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The local compositional heterogeneity associated with the lack of long-range ordering of Mg 2+ and Nb 5+ in PbMg 1/3 Nb 2/3 O 3 (PMN) is correlated with its characteristic "relaxor" ferroelectric behavior. Earlier work [Shetty et al., Adv. Funct. Mater. 29, 1804258 (2019)] examined the relaxor behavior in PMN thin films grown at temperatures below 1073 K by artificially reducing the degree of disorder via synthesis of heterostructures with alternate layers of Pb(Mg 2/3 Nb 1/3 )O 3 and PbNbO 3 , as suggested by the "random-site model." This work confirmed the development of ferroelectric domains below 150 K in long-range-ordered films, epitaxially grown on (111) SrTiO 3 substrates using alternate target timed pulsed-laser deposition of Pb(Mg 2/3 Nb 1/3 )O 3 and PbNbO 3 targets with 20% excess Pb. In this work, the first through third-harmonic dielectric charge displacement densities and complex dielectric susceptibilities were analyzed as a function of temperature and frequency in zero-field-cooled PMN films with short-and long-range ordering. The long-range ordering decreased the dispersion in the firstand third-harmonic dielectric charge displacement densities relative to short-range-ordered films. It was found that the one-dimensional ordering achieved in the long-range-ordered film is insufficient to achieve a fully normal ferroelectric state. In the presence of quenched random electric fields, these films require a small ac field to facilitate percolation of the polar nano-regions, enabling normal ferroelectriclike behavior at lower temperature (T < 240 K). The films behave like a typical relaxor near room temperature. With reduced ordering, the short-range films exhibit greater dispersion in linear and higher order harmonic dielectric charge displacement density.