Structure, Performance, and Application of BiFeO_(3) Nanomaterials

Multiferroic nanomaterials have attracted great interest due to simultaneous two or more properties such as ferroelectricity,ferromagnetism,and ferroelasticity,which can promise a broad application in multifunctional,lowpower consumption,environmentally friendly devices.Bismuth ferrite(BiFeO3,BFO)exhibits both(anti)ferromagnetic and ferroelectric properties at room temperature.Thus,it has played an increasingly important role in multiferroic system.In this review,we systematically discussed the developments of BFO nanomaterials including morphology,structures,properties,and potential applications in multiferroic devices with novel functions.Even the opportunities and challenges were all analyzed and summarized.We hope this review can act as an updating and encourage more researchers to push on the development of BFO nanomaterials in the future.

Regulated polarization degree of upconversion luminescence and multiple anti-counterfeit applications

Polarization upconversion luminescence(PUCL)of lanthanide ions(Ln^(3+))has been widely used in single particle tracking,microfluidics detection,three-dimensional displays,and so on.However,no effective strategy has been developed for modulating PUCL.Here we report a strategy to regulate PUCL in Ho^(3+)-doped NaYF4single nanorods based on the number of upconversion photons.By constructing a multiphoton upconversion system for Ho^(3+),we regulate the degree of polarization(DOP)of PUCL from 0.590 for two-photon luminescence to 0.929 for three-photon upconversion luminescence(UCL).Furthermore,our strategy is verified from cross-relaxation between Ho^(3+)and Yb^(3+),excitation wavelength,excitation power density,and local site symmetry.And this regulation strategy of PUCL has also been achieved in Tm^(3+),with the DOP ranging from 0.233 for two-photon luminescence to 0.925 for four-photon UCL Besides,multi-dimensional anti-counterfeiting display has been explored with PUCL.This work provides an effective strategy for regulating PUCL and also provides more opportunities for the development of polarization display optical encoding,anti-counterfeiting,and integrated optical devices.

Tribotronic bipolar junction transistor for mechanical frequency monitoring and use as touch switch

Tribotronics,a new field that involves the coupling of triboelectricity and semiconductors,has attracted great interest in the nanoenergy and nanoelectronics domains.This paper proposes a tribotronic bipolar junction transistor(TBJT)that incorporates a bipolar junction transistor and a triboelectric nanogenerator(TENG)in the single-electrode mode.When the mobile triboelectric layer slides on the device surface for electrification,a bias voltage is created and applied to the emitter junction,and then the base current from the TENG is amplified.Based on the fabricated TBJT,a mechanical frequency monitoring sensor with high sensitivity and excellent stability and a finger-triggered touch switch were developed.This work demonstrated for the first time a tribotronic device with simultaneously controlled voltage and current voltage/current simultaneously controlled tribotronic device,which has promising potential applications in micro/nano-sensors,human-machine interactions,intelligent instrumentation,wearable electronics,and other applications.

Flexoelectricity-enhanced photovoltaic effect in trapezoid-shaped NaNbO_(3)nanotube array composites

In this work,we successfully prepared vertically aligned NaNbO_(3)nanotube(NN-NT)with trapezoidal shapes,in which the orthorhombic and monoclinic phases coexisted.According to the structure analysis,the NN-NT/epoxy composite film had excellent flexoelectric properties due to the lattice distortion caused by defects and irregular shape.The flexoelectric effect is the greatest in the vertical direction in the flexible NN-NT/epoxy composite film,and the flexoelectric coefficient()is 2.77×10^(−8)C·m^(−1),which is approximately 5-fold higher than that of the pure epoxy film.The photovoltaic current of the NN-NT/epoxy composite film increased from 39.9 to 71.8 nA·cm^(−2)in the direction of spontaneous polarization when the sample was bent upward due to the flexoelectricity-enhanced photovoltaic(FPV)effect.The flexoelectric effect of the NN-NT/epoxy composite film could modulate the photovoltaic response by increasing it by 80%or reducing it to 65%of the original value.This work provides a new idea for further exploration in efficient and lossless ferroelectric memory devices.