Role of charged defects in resistance fatigue of ferroelectric tunnel junctions has been revealed at atomic scale.

Materials showing type II Dirac fermions can generate abundant physical properties. NiTe2 is a type-II Dirac semimetal, however, most of the synthesis methods for 2D NiTe2 require a high temperature (>550 °C) or complex manipulations, leading to environmentally unstable products. Herein, a facile solvothermal method is designed to prepare NiTe2 nanosheets. Significantly, a NiTe2 nanosheet-based flexible photodetector responds with high sensitivy to wide range incident light from 450 to 1550 nm. Moreover, the NiTe2 nanosheets maintain high environmental stability for 30 days, and the output current of the device shows negligible decay over time.

Recently, rapidly increased demands of integration and miniaturization continuously challenge energy densities of dielectric capacitors. New materials with high recoverable energy storage densities become highly desirable. Here, by structure evolution between fluorite HfO2 and perovskite hafnate, we create an amorphous hafnium-based oxide that exhibits the energy density of ~155 J/cm3 with an efficiency of 87%, which is state-of-the-art in emergingly capacitive energy-storage materials. The amorphous structure is owing to oxygen instability in between the two energetically-favorable crystalline forms, in which not only the long-range periodicities of fluorite and perovskite are collapsed but also more than one symmetry, i.e., the monoclinic and orthorhombic, coexist in short range, giving rise to a strong structure disordering. As a result, the carrier avalanche is impeded and an ultrahigh breakdown strength up to 12 MV/cm is achieved, which, accompanying with a large permittivity, remarkably enhances the energy storage density. Our study provides a new and widely applicable platform for designing high-performance dielectric energy storage with the strategy exploring the boundary among different categories of materials.

Recently, relaxor ferroelectric thin-film capacitors have attracted considerable attention for energy storage applications since their slim-type polarization–electric field hysteresis loops can yield large recoverable energy density ( Wrec) and high efficiency ( η). In this work, we study the effects of buffer layers on energy storage properties of 0.93Pb(Mg1/3Nb2/3)O3-0.07PbTiO3 (PMN-PT) thin-film capacitors with a 5 nm-thick SrTiO3 (STO) and LaAlO3 (LAO) films. The energy storage properties of Pt/PMN-PT/SrRuO3 (SRO) capacitors are found to be significantly changed by incorporating the STO or LAO buffer layer at the top Pt/PMN-PT interface, while inserting the buffer layer at bottom PMN-PT/SRO interface shows negligible effects on the electrical properties. Specifically, with the STO buffering, the breakdown field is dramatically increased in the Pt/STO/PMN-PT/SRO capacitor due to the existence of an internal field in the STO, which prevents the growth of electrical trees from the bottom SRO to the top Pt electrode, and a large Wrec of ∼48.91 J/cm3, more than three times of that of the PMN-PT capacitor, is achieved. However, buffered by the LAO, the Pt/LAO/PMN-PT/SRO capacitor exhibits a reduced relaxor character, which may be ascribed to a pinning effect of nanodomains associated with the charged LAO/PMN-PT interface. As a result, both Wrec and η are significantly lowered, compared to the non-buffered PMN-PT capacitor. These results provide physical insights into the modulation of relaxor and dielectric behaviors by designing the characteristics of buffer layers, demonstrating a way for enhancing energy storage properties in thin-film capacitors.

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