Haizhong Guo

Current-voltage hysteresis and switchable rectifying characteristics have been observed in epitaxial multiferroic BiFeO3 (BFO) thin films. The forward direction of the rectifying current can be reversed repeatedly with polarization switching, indicating a switchable diode effect and large ferroelectric resistive switching. With analyzing the potential barriers and their variation with ferroelectric switching at the interfaces between the metallic electrodes and the semiconducting BFO, the switchable diode effect can be explained qualitatively by the polarization-modulated Schottky-like barriers.

Abstract High‐performance flexible pressure sensors have attracted a great deal of attention, owing to its potential applications such as human activity monitoring, man–machine interaction, and robotics. However, most high‐performance flexible pressure sensors are complex and costly to manufacture. These sensors cannot be repaired after external mechanical damage and lack of tactile feedback applications. Herein, a high‐performance flexible pressure sensor based on MXene/polyurethane (PU)/interdigital electrodes is fabricated by using a low‐cost and universal spray method. The sprayed MXene on the spinosum structure PU and other arbitrary flexible substrates (represented by polyimide and membrane filter) act as the sensitive layer and the interdigital electrodes, respectively. The sensor shows an ultrahigh sensitivity (up to 509.8 kPa –1 ), extremely fast response speed (67.3 ms), recovery speed (44.8 ms), and good stability (10 000 cycles) due to the interaction between the sensitive layer and the interdigital electrodes. In addition, the hydrogen bond of PU endows the device with the self‐healing function. The sensor can also be integrated with a circuit, which can realize tactile feedback function. This MXene‐based high‐performance pressure sensor, along with its designing/fabrication, is expected to be widely used in human activity detection, electronic skin, intelligent robots, and many other aspects.

In recent years, inorganic CsPbBr₃-based perovskites have accomplished considerable progress owing to their superior stability under harsh humid environment.

Zirconium oxide (ZrO2 or zirconia) nanostructures were synthesized by a hydrothermal route. Surface morphology analysis depicts the formation of various zirconia nanostructures at different synthesis conditions. X-ray diffraction examination demonstrates that the as-synthesized zirconia is of pure monoclinic phase (m-ZrO2). High resolution transmission electron microscopy (HRTEM) further confirms the high crystalline feature of the m-ZrO2 nanostructures. X-ray photoelectron spectroscopy (XPS) core-level spectra of Zr 3d and O 1s for the ZrO2 nanostructures have been studied to understand further the electronic states and chemical environment of the Zr and O atoms in ZrO2 for different synthesis conditions. XPS results also indicate the existence of oxygen defects and zirconia suboxides which affect the structural and optical properties of zirconia nanostructures. The nanostructures show UV−vis absorption band around 290 nm at room temperature. The band gap energy is determined, in the range of 2.5−3.8 eV for zirconia nanostructures synthesized at various conditions. A broad emission band with maximum intensity at around 400 nm is observed in the photoluminescence (PL) spectra of zirconia nanostructures at room temperature depicting the violet emission, which can be attributed to the ionized oxygen vacancy in the material.

Abstract Perovskite‐structured (ABO 3 ) transition metal oxides are promising bifunctional electrocatalysts for efficient oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). In this paper, a set of epitaxial rare‐earth nickelates (RNiO 3 ) thin films is investigated with controlled A‐site isovalent substitution to correlate their structure and physical properties with ORR/OER activities, examined by using a three‐electrode system in O 2 ‐saturated 0.1 m KOH electrolyte. The ORR activity decreases monotonically with decreasing the A‐site element ionic radius which lowers the conductivity of RNiO 3 (R = La, La 0.5 Nd 0.5 , La 0.2 Nd 0.8 , Nd, Nd 0.5 Sm 0.5 , Sm, and Gd) films, with LaNiO 3 being the most conductive and active. On the other hand, the OER activity initially increases upon substituting La with Nd and is maximal at La 0.2 Nd 0.8 NiO 3 . Moreover, the OER activity remains comparable within error through Sm‐doped NdNiO 3 . Beyond that, the activity cannot be measured due to the potential voltage drop across the film. The improved OER activity is ascribed to the partial reduction of Ni 3+ to Ni 2+ as a result of oxygen vacancies, which increases the average occupancy of the e g antibonding orbital to more than one. The work highlights the importance of tuning A‐site elements as an effective strategy for balancing ORR and OER activities of bifunctional electrocatalysts.