Abstract
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 BiFeO
3
films. The BiFeO
3
film epitaxially grown on SrTiO
3
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 BiFeO
3
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 BiFeO
3
. The strain gradient induced multilevel photoconductance shows very good reproducibility by bending the flexible BiFeO
3
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.
Realization of functional flexible artificial synapse is a significant step toward neuromorphic computing. Herein, a flexible artificial synapse based on ferroelectric tunnel junctions (FTJs) is ...demonstrated, using BiFeO
3
(BFO) thin film as the functional layer. The inorganic single crystalline FTJs grown on rigid perovskite substrates at high temperatures are integrated with the flexible plastic substrates, by using the water-soluble Sr
3
Al
2
O
6
(SAO) as the sacrificial layer and the following transfer. The transferred freestanding BFO thin film exhibits excellent ferroelectric properties. Moreover, the memristive properties and the brain-like synaptic learning performance of the flexible FTJs are investigated. The results show that multilevel resistance states were maintained well of the flexible artificial synapse, together with their stable synaptic learning properties. Our work indicates the promising opportunity of ferroelectric thin film based flexible synapse used in the future neuromorphic computing system.
Ferroelectricity features the electrical switching of off-centered ions between the potential double well of the non-centrosymmetric lattice, while ionic conduction requires long-range hopping of ...ions across the lattice periodic potentials. The two seemingly mutually exclusive phenomena become strongly intertwined at the nanoscale in electrochemically active materials. However, the intrinsic coupling between ferroelectric switching and ionic activities in bulk crystalline materials remains largely unexplored. Here, we report anomalous polarization switching characteristics of a van der Waals (vdW) layered ferroelectric ionic conductor, CuInP
2
S
6
. By synergistic polarization switching and dielectric spectroscopy studies in both temperature and frequency domains, we reveal that the polarization switching kinetics of this compound is ionic-conduction-limited, due to the strong electrostatic interaction between ferroelectric and ionic defect dipoles. The crucial role of thermally-activated displacive instability of Cu ions is confirmed by the single-crystal X-ray crystallography results. The findings provide fundamental insight into the ionic kinetics under an electric field in crystals with coexisting dipole order (ferroelectricity) and disorder (ionic defect and conductivity). Last but not least, we demonstrate that the spontaneous ionic defect-polarization interlock can lead to permanent ferroelectric retention, which is essential for information storage.
Ionic conduction in a ferroelectric leads to anomalous polarization switching kinetics but prevents retention failure.
Epitaxial strain can cause both lattice distortion and oxygen nonstoichiometry, effects that are strongly coupled at heterojunctions of complex nickelate oxides. Here we decouple these structural and ...chemical effects on the oxygen evolution reaction (OER) by using a set of coherently strained epitaxial NdNiO3 films. We show that within the regime where oxygen vacancies (VO) are negligible, compressive strain is favorable for the OER whereas tensile strain is unfavorable; the former induces orbital splitting, resulting in a higher occupancy in the d3z 2−r 2 orbital and weaker Ni–O chemisorption. However, when the tensile strain is sufficiently large to promote VO formation, an increase in the OER is also observed. The partial reduction of Ni3+ to Ni2+ due to VO makes the eg occupancy slightly larger than unity, which is thought to account for the increased OER activity. Our work highlights that epitaxial-strain-induced lattice distortion and VO generation can be individually or collectively exploited to tune OER activity, which is important for the predictive synthesis of high-performance electrocatalysts.
The ferroelectric photovoltaic effect has been extensively studied for possible applications in energy conversion and photo-electrics. The reversible spontaneous polarization gives rise to a ...switchable photovoltaic behavior. However, despite its long history, the origin of the ferroelectric photovoltaic effect still lacks a full understanding since multiple mechanisms such as bulk and Schottky-barrier-related interface effects are involved. Herein, we report a comprehensive study on the photovoltaic response of BiFeO3-based vertical heterostructures, using multiple strategies to clarify its origin. We found that, under white light illumination, polarization-modulated Schottky barrier at the interface is the dominating mechanism. By varying the top metal contacts, only the photovoltaic effect of the polarization downward state is strongly modulated, suggesting selective interface contribution in different polarization states. A Schottky-barrier-free device shows negligible photovoltaic effect, suggesting the lack of bulk photovoltaic effect in vertical heterostructures under white light illumination.
The ferroelectric photovoltaic effect has been extensively studied for possible applications in energy conversion and photo-electrics. The reversible spontaneous polarization gives rise to a ...switchable photovoltaic behavior. However, despite its long history, the origin of the ferroelectric photovoltaic effect still lacks a full understanding since multiple mechanisms such as bulk and Schottky-barrier-related interface effects are involved. Herein, we report a comprehensive study on the photovoltaic response of BiFeO
-based vertical heterostructures, using multiple strategies to clarify its origin. We found that, under white light illumination, polarization-modulated Schottky barrier at the interface is the dominating mechanism. By varying the top metal contacts, only the photovoltaic effect of the polarization downward state is strongly modulated, suggesting selective interface contribution in different polarization states. A Schottky-barrier-free device shows negligible photovoltaic effect, suggesting the lack of bulk photovoltaic effect in vertical heterostructures under white light illumination.
Epitaxial strain can cause both lattice distortion and oxygen nonstoichiometry, effects that are strongly coupled at heterojunctions of complex nickelate oxides. Here we decouple these structural and ...chemical effects on the oxygen evolution reaction (OER) by using a set of coherently strained epitaxial NdNiO
films. We show that within the regime where oxygen vacancies (V
) are negligible, compressive strain is favorable for the OER whereas tensile strain is unfavorable; the former induces orbital splitting, resulting in a higher occupancy in the d
orbital and weaker Ni-O chemisorption. However, when the tensile strain is sufficiently large to promote V
formation, an increase in the OER is also observed. The partial reduction of Ni
to Ni
due to V
makes the e
occupancy slightly larger than unity, which is thought to account for the increased OER activity. Our work highlights that epitaxial-strain-induced lattice distortion and V
generation can be individually or collectively exploited to tune OER activity, which is important for the predictive synthesis of high-performance electrocatalysts.
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