A flexible quasi-solid-state Ni-Zn battery is developed by using tiny ZnO nanoparticles and porous ultrathin NiO nanoflakes conformally deposited on hierar chical carbon-cloth-carbon-fiber (CC-CF) as the anode (CC-CF@ZnO) and cathode (CC-CF@NiO), respectively. The device is able to deliver high performance (absence of Zn dendrite), superior to previous reports on aqueous Ni-Zn batteries and other flexible electrochemical energy-storage devices.
Ferroelectricity has been believed to be an important but controversial origin of the excellent photovoltaic performance of organometal trihalide perovskites (OTPs). Here we investigate the ferroelectricity of a prototype OTP, CH3NH3PbI3 (MAPbI3), both theoretically and experimentally. Our first-principles calculations based on 3-D periodic boundary conditions reveal that a ferroelectric structure with polarization of ∼8 μC/cm(2) is the globally stable one among all possible tetragonal structures; however, experimentally no room-temperature ferroelectricity is observed by using polarization-electric field hysteresis measurements and piezoresponse force microscopy. The discrepancy between our theoretical and experimental results is attributed to the dynamic orientational disorder of MA(+) groups and the semiconducting nature of MAPbI3 at room temperature. Therefore, we conclude that MAPbI3 is not ferroelectric at room temperature; however, it is possible to induce and experimentally observe apparent ferroelectric behavior through our proposed ways. Our results clarify the controversy of the ferroelectricity in MAPbI3 and also provide valuable guidance for future studies on this active topic.
Among the different types of multiferroic compounds, bismuth ferrite (BiFeO 3 ; BFO) stands out because it is perhaps the only one being simultaneously magnetic and strongly ferroelectric at room temperature. Therefore, in the past decade or more, extensive research has been devoted to BFO-based materials in a variety of different forms, including ceramic bulks, thin films and nanostructures. Ceramic bulk BFO and their solid solutions with other oxide perovskite compounds show excellent ferroelectric and piezoelectric properties and are thus promising candidates for lead-free ferroelectric and piezoelectric devices. BFO thin films, on the other hand, exhibit versatile structures and many intriguing properties, particularly the robust ferroelectricity, the inherent magnetoelectric coupling, and the emerging photovoltaic effects. BFO-based nanostructures are of great interest owing to their size effect-induced structural modification and enhancement in various functional behaviors, such as magnetic and photocatalytic properties. Although to date several
Ferroelectric random access memory (FeRAM) based on conventional ferroelectric perovskites, such as Pb(Zr,Ti)O 3 and SrBi 2 Ta 2 O 9 , has encountered bottlenecks on memory density and cost, because those conventional perovskites suffer from various issues mainly including poor complementary metal-oxide-semiconductor (CMOS)-compatibility and limited scalability. Nextgeneration cost-efficient, high-density FeRAM shall therefore rely on a material revolution. Since the discovery of ferroelectricity in Si:HfO 2 thin films in 2011, HfO 2 -based materials have aroused widespread interest in the field of FeRAM, because they are CMOScompatible and can exhibit robust ferroelectricity even when the film thickness is scaled down to below 10 nm. A review on this new class of ferroelectric materials is therefore of great interest. In this paper, the most appealing topics about ferroelectric HfO 2 -based materials including origins of ferroelectricity, advantageous material properties, and current and potential applications in FeRAM, are briefly reviewed.
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