SrFeO x (SFO x ) compounds exhibit ionic conduction and oxygen-related phase transformation, having potential applications in solid oxide fuel cells, smart windows, and memristive devices. The phase transformation in SFO x typically requires a thermal annealing process under various pressure conditions, hindering their practical applications. Here, we have achieved a reversible phase transition from brownmillerite (BM) to perovskite (PV) in SrFeO2.5 (SFO2.5) films through ionic liquid (IL) gating. The real-time phase transformation is imaged using in situ high-resolution transmission electron microscopy. The magnetic transition in SFO2.5 is identified by fabricating an assisted La0.7Sr0.3MnO3 (LSMO) bottom layer. The IL-gating-converted PV phase of a SrFeO3−δ (SFO3−δ) layer shows a ferromagnetic-like behavior but applies a huge pinning effect on LSMO magnetic moments, which consequently leads to a prominent exchange bias phenomenon, suggesting an uncompensated helical magnetic structure of SFO3−δ. On the other hand, the suppression of both magnetic and exchange coupling signals for a BM-phased SFO2.5 layer elucidates its fully compensated G-type antiferromagnetic nature. We also demonstrated that the phase transition by IL gating is an effective pathway to tune the resistive switching parameters, such as set, reset, and high/low-resistance ratio in SFO2.5-based resistive random-access memory devices.

Negative capacitance effect in ferroelectric materials provides a solution to the energy dissipation problem induced by Boltzmann distribution of electrons in conventional electronics. Here, we discover that besides ferroelectrics, the antiferroelectrics based on Landau switches also have intrinsic negative capacitance effect. We report both the static and transient negative capacitance effect in antiferroelectric PbZrO3 films and reveal its possible physical origin. The capacitance of the capacitor of the PbZrO3 and paraelectric heterostructure is demonstrated to be larger than that of the isolated paraelectric capacitor at room temperature, indicating the existence of the static negative capacitance. The opposite variation trends of the voltage and charge transients in a circuit of the PbZrO3 capacitor in series with an external resistor demonstrate the existence of transient negative capacitance effect. Strikingly, four negative capacitance effects are observed in the antiferroelectric system during one cycle scan of voltage pulses, different from the ferroelectric counterpart with two negative capacitance effects. The polarization vector mapping, electric field and free energy analysis reveal the rich local regions of negative capacitance effect with the negative dP/dE and (δ2G)⁄(δD2), producing stronger negative capacitance effect. The observation of negative capacitance effect in antiferroelectric films significantly extends the range of its potential application and reduces the power dissipation further.

In this work, we report the synthesis of composite system pNAC, composed of silver nanoparticles embedded in pure thermo-sensitive crosslinked polymer network of poly(N-isopropylacrylamide-co-acrylamide) (pNA), using as a catalyst for the reduction of methylene blue (MB) dye by sodium borohydride (NaBH 4 ). The pNA was prepared by conventional free radical polymerization technique using sodium dodecyl sulfate as stabilizing agent, followed by in situ reduction of AgNO 3 inside the polymer network by NaBH 4 for the synthesis of composite systems pNACs. The synthesized pNA and pNACs were characterized by FTIR, dynamic light scattering, thermogravimetric analysis, scanning electron microscopy and UV-visible spectroscopy techniques. The materials were found sensitive toward temperature change of the medium. The entrapment ability of pNA toward different amounts of AgNO 3 solution was studied, and effect of metal content on particle size of pNACs was analyzed. The pNACs were applied as a catalyst for the reduction of MB in which they exhibit high catalytic activity and reusability toward the reaction.

Interfaces between materials provide an intellectually rich arena for fundamental scientific discovery and device design. However, the frustration of magnetization and conductivity of perovskite oxide films under reduced dimensionality is detrimental to their device performance, preventing their active low-dimensional application. Herein, by inserting the ultrathin 4d ferromagnetic SrRuO3 layer between ferroelectric BaTiO3 layers to form a sandwich heterostructure, we observe enhanced physical properties in ultrathin SrRuO3 films, including longitudinal conductivity, Curie temperature, and saturated magnetic moment. Especially, the saturated magnetization can be enhanced to ∼3.12 μB/Ru in ultrathin BaTiO3/SrRuO3/BaTiO3 trilayers, which is beyond the theoretical limit of bulk value (2 μB/Ru). This observation is attributed to the synergistic ferroelectric proximity effect (SFPE) at upper and lower BaTiO3/SrRuO3 heterointerfaces, as revealed by the high-resolution lattice structure analysis. This SFPE in dual-ferroelectric interface cooperatively induces ferroelectric-like lattice distortions in RuO6 oxygen octahedra and subsequent spin-state crossover in SrRuO3, which in turn accounts for the observed enhanced magnetization. Besides the fundamental significance of interface-induced spin–lattice coupling, our findings also provide a viable route to the electrical control of magnetic ordering, taking a step toward low-power applications in all-oxide spintronics.

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