The quest for a solid state universal memory with high-storage density, high read/write speed, random access and non-volatility has triggered intense research into new materials and novel device architectures. Though the non-volatile memory market is dominated by flash memory now, it has very low operation speed with ~10 μs programming and ~10 ms erasing time. Furthermore, it can only withstand ~105 rewriting cycles, which prevents it from becoming the universal memory. Here we demonstrate that the significant photovoltaic effect of a ferroelectric material, such as BiFeO3 with a band gap in the visible range, can be used to sense the polarization direction non-destructively in a ferroelectric memory. A prototype 16-cell memory based on the cross-bar architecture has been prepared and tested, demonstrating the feasibility of this technique.

OER) are two of the most important electrochemical reactions that limit the efficiencies of fuel cells, metal-air batteries, and electrolytic water-splitting. [4][5][6][7] Although some noble metals and their associated compounds, such as Pt, RuO 2 , and IrO 2 , exhibit high ORR or OER catalytic activity, [8][9][10][11][12] the high cost and scarcity of such precious metals prevent their large-scale use. [13,14] 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.

Doped‐HfO2 thin films with ferroelectricity have attracted great attention due to their potential application in semiconductor industry as negative capacitance and resistance switching memory. Despite Hf0.5Zr0.5O2 (HZO) thin films having the most robust ferroelectric properties among all doped‐HfO2 thin films, the realization of single orthorhombic phase HZO thin films is not achieved, while the direct evidence between the structural–properties relationship of orthorhombic phase HZO and ferroelectricity is not confirmed. In this work, the growth of single orthorhombic phase HZO thin films with decent ferroelectricity and resistive switching behavior is reported. With the aid of advanced structural characterization techniques, the HZO thin film is confirmed to be in the single orthorhombic phase. Next, using scanning probe microscopy techniques and macroscopic ferroelectric measurements, the single phase HZO thin films exhibit ferroelectric properties with a remanent polarization of about 20 µC cm−2. Interestingly, the HZO thin film shows ferroelectric resistive switching with an ROFF/RON ratio of about 16 100% with excellent device performance. Furthermore, brain‐like learning behavior is also observed in the HZO thin film. These results may serve to stimulate the study of ferroelectric properties of HZO thin films and their application in the electronic industry.

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Flexoelectricity induced by the strain gradient is attracting much attention due to its potential applications in electronic devices. Here, by combining a tunable flexoelectric effect and the ferroelectric photovoltaic effect, we demonstrate the continuous tunability of photoconductance in BiFeO3 films. The BiFeO3 film epitaxially grown on SrTiO3 is transferred to a flexible substrate by dissolving a sacrificing layer. The tunable flexoelectricity is achieved by bending the flexible substrate which induces a nonuniform lattice distortion in BiFeO3 and thus influences the inversion asymmetry of the film. Multilevel conductance is thus realized through the coupling between flexoelectric and ferroelectric photovoltaic effect in freestanding BiFeO3. The strain gradient induced multilevel photoconductance shows very good reproducibility by bending the flexible BiFeO3 device. This control strategy offers an alternative degree of freedom to tailor the physical properties of flexible devices and thus provides a compelling toolbox for flexible materials in a wide range of applications.