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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 nonmetallic elements (i.e., hydrogen and nitrogen) can open up more possibilities for preparing novel families of electronically active oxide compounds. Fast and reversible uptake and release of hydrogen in epitaxial ABO3 manganite films through an adapted low-frequency inductively coupled plasma technology is introduced. 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 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 transition is achieved at a relatively low temperature (T ≤ 350 °C), enabling multifunctional 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.

The chemical and electronic interactions at metal/oxide heterojunctions is pivotal in determining the electronic properties of oxide devices utilized in microelectronics, catalysis, and photovoltaic systems. In this study, interfacial oxidation migrations within a model heterostructure system, consisting of a La0.7Sr0.3MnO3 film overlaid by various metallic (Ti, Al, Cu, Ag, and Au) ultrathin layers are systematically investigated. It is experimentally demonstrated that at elevated deposition temperature, the oxygen‐active ultrathin overlayers of base metals such as Ti and Al significantly derive oxygen from the underlying La0.7Sr0.3MnO3 film, inducing a perovskite to brownmillerite phase transition in the underlying functional oxide film. Conversely, no structural transitions are observed for La0.7Sr0.3MnO3 film when it is capped by noble metals (Au, Ag), which possess relative high oxidation formation energy. These observations are crucial for the development of novel crystalline and electronic architectures in metal/oxide heterostructures, offering a refined approach to modulate interfacial reactivity without compromising the functionality of oxide‐based heterojunction devices. [ABSTRACT FROM AUTHOR]

The high‐efficient and low‐cost oxygen evolution reaction (OER) is decisive for applications of oxide catalysts in metal‐air batteries, electrolytic cells, and energy‐storage technologies. Delicate regulations of active surface and catalytic reaction pathway of oxide materials principally determine thermodynamic energy barrier and kinetic rate during catalytic reactions, and thus have crucial impacts on OER performance. Herein, a synergistic modulation of catalytically active surface and reaction pathway through facile topotactic transformations switching from perovskite (PV) LaNiO3.0 film to infinite‐layer (IL) LaNiO2.0 film is demonstrated, which absolutely contributes to improving OER performance. The square‐planar NiO4 coordination of IL‐LaNiO2.0 brings about more electrochemically active metal (Ni+) sites on the film surface. Meanwhile, the oxygen‐deficient driven PV‐ IL topotactic transformations lead to a reaction pathway converted from absorbate evolution mechanism to lattice‐oxygen‐mediated mechanism (LOM). The non‐concerted proton–electron transfer of LOM pathway, evidenced by the pH‐dependent OER kinetics, further boosts the OER activity of IL‐LaNiO2.0 films. These findings will advance the in‐depth understanding of catalytic mechanisms and open new possibilities for developing highly active perovskite‐derived oxide catalysts. [ABSTRACT FROM AUTHOR]

Electric‐field regulation of magnetic properties in perovskite manganites has attracted much attention for its potential in spintronics. For antiferromagnetic perovskite manganites, fewer studies are reported due to technological difficulties in probing their magnetic properties. Here, negative exchange bias (EB) is realized in epitaxial antiferromagnetic/ferromagnetic manganite bilayers with atomically flat interfaces. The low‐voltage pulse modulation of EB is demonstrated using the field‐effect device geometry with the ferroelectric copolymer, polyvinylidene fluoride with trifluoroethylene as a dielectric gating layer, antiferromagnetic La0.35Sr0.65MnO3 (AF‐LSMO) as pinning layer, and ferromagnetic La0.7Sr0.3MnO3 (FM‐LSMO) as conduction channel. Instead of using non‐volatile polarizations to control the EB, volatile polarizations in ferroelectric field effect transistors are suggested to be capable of modulating the EB. With high‐resolution electron microscopy and spectroscopy, the non‐volatile regulation of EB is attributed to the creation/annihilation of oxygen vacancies in the AF‐LSMO layer via low‐voltage pulses. This study reveals the effect of volatile electric polarizations in ferroelectric field effect devices and highlights the potential for low‐voltage pulse control of the physical properties in antiferromagnetic perovskite oxide insulators. [ABSTRACT FROM AUTHOR]

Although epitaxial strain imparted by lattice mismatch between a film and the underlying substrate has led to distinct structures and emergent functionalities, the discrete lattice parameters of limited substrates, combined with strain relaxations driven by film thickness, result in severe obstructions to subtly regulate electro‐elastic coupling properties in perovskite ferroelectric films. Here a practical and universal method to achieve highly strained phases with large tetragonal distortions in Pb‐based ferroelectric films through synergetic effects of moderately (≈1.0%) misfit strains and laser fluences during pulsed laser deposition process is demonstrated. The phase possesses unexpectedly large Poisson's ratio and negative thermal expansion, and concomitant enhancements of spontaneous polarization (≈100 µC cm−2) and Curie temperature (≈800 °C), 40% and 75% larger than that of bulk counterparts, respectively. This strategy efficiently circumvents the long‐standing issue of limited numbers of discrete substrates and enables continuous regulations of exploitable lattice states in functional oxide films with tightly elastic coupled performances beyond their present levels. [ABSTRACT FROM AUTHOR]

Negative and near-zero Poisson's ratio materials are mechanical metamaterials that host an improved strain energy absorption property with respect to conventional materials. By using first-principles calculations, we report the negative and near-zero Poisson's ratios in van der Waals (vdW) heterostructures, such as graphene/hexagonal molybdenum disulfide (G/MoS2) and graphene/hexagonal boron nitride (G/h-BN), sharing distinct crystal structures from all other known negative and near-zero Poisson's ratio materials. However, the Poisson's ratios of the interfacial layer in bilayer MoS2 and h-BN are positive and near-zero along the out-of-plane direction, respectively, which are quite different from the Poisson's ratios of G/MoS2 and G/h-BN heterostructures. Therefore, these behaviors are unique to vdW heterostructures. We attribute these negative Poisson's ratio behaviors to the special interaction of pz orbitals between the interfacial layers. Furthermore, we observed among them high-order elastic constants in the out-of-plane direction, which exhibit nonlinear stress–strain responses. These results are significant for the preparation of G/h-BN and G/MoS2 heterostructures. The combinations of tunable negative/near-zero Poisson's ratios with the excellent electrical/optical properties of G/MoS2 and G/h-BN heterostructures will pave the way to a wide range of applications in novel auxetic molecular sieves and electrodes. [ABSTRACT FROM AUTHOR]

The occurrence of ferroelectric charged domain walls (CDWs) which was thought to be energetically unstable is observed, together with a ferroelectric vortex structure composed of 109° and 180° domains near an epitaxial BiFeO3/GdScO3 interface. The CDW and vortex affect the domain arrangement, domain configuration, and hence tune the domain size distribution. [ABSTRACT FROM AUTHOR]