Qiuyun Fu

Physically Flexible, Rapid‐Response Gas Sensor Based on Colloidal Quantum Dot Solids

A gas sensor based on PbS colloidal quantum dots (CQDs) is constructed on a paper substrate, yielding flexible, rapid-response NO₂ gas sensors, fabricated from the solution phase. The devices are highly sensitive and fully recoverable at room temperature, which is attributed to the excellent access of gas molecules to the CQD surface, realized by surface ligand removal, combined with the desirable binding energy of NO₂ with the PbS CQDs.

Theoretical Analysis of Wireless Passive Impedance-Loaded SAW Sensors

This paper concentrates on the theoretical analysis of wireless passive surface acoustic wave (SAW) impedance-loaded sensors. A general method is proposed for simulating the impedance-loaded SAW sensors. It is based on the combined finite-element method and boundary element method (FEM/BEM). A FEM is used to account for the mass loading effect of electrodes and a Greens function is used to model the piezoelectric substrate. Comparison between the simulations and measurements on SAW devices shows a good agreement. The calculated amplitude variation of the impulse response in time domain shows a resonant characteristic with the change of the loaded impedance. It is found that the return loss reaches the maximum value when the resonant frequency of the loaded circuits matches the center frequency of the short-circuited SAW transponder. This phenomenon is successfully explained by using the proposed model. Some high-performance sensors with greater amplitude modulation and larger sensitive range could be designed using this method.

Grain-oriented sodium bismuth titanate-based lead-free piezoelectric ceramics prepared using the pulsed strong magnetic field and template grain growth

In this paper, 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 (BNBT6) lead-free piezoelectric ceramics have been prepared using the gelcasting technology. The dielectric and piezoelectric properties of these ceramics have been investigated. The specimens were sintered at 1100–1200 °C after grain-oriented under the pulsed strong magnetic field during the solidification of the green bodies. Compared with the BNBT6 samples without applying magnetic field, the ceramics textured by applying 5 T pulsed magnetic field has a coercive field with reduction of 400 V/mm, which makes the polarization process easier. Meanwhile, it is noted that the orientation degree increases with increasing sintering temperature, whereas the piezoelectric constant and electromechanical coupling coefficients are improved. If SrTiO3 seed grain is introduced, the orientation degree can reach 0.70 and the relative density of the sintered ceramics is up to 96%. The dielectric properties are anisotropic in directions vertical and parallel to the applied ma...

Growth and characterization of all-inorganic lead halide perovskite semiconductor CsPbBr3 single crystals

As a typical representative of all-inorganic lead halide perovskites, cesium lead bromide (CsPbBr3) has attracted significant attention in the context of photovoltaics and other optoelectronic applications in recent years. In this paper, CsPbBr3 single crystal growth was conducted by a creative electronic dynamic gradient (EDG) method. The crystal structure was systematically investigated using scientific instruments and equipment. X-ray diffraction techniques, including X-ray diffraction (XRD), temperature-dependent X-ray powder diffraction and the X-ray rocking curve, were used to identify the phase and to investigate phase transition rules. Electron diffraction techniques, including high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and electron backscatter diffraction (EBSD), were used to investigate the crystal micro-structure. The final results indicated that the grown CsPbBr3 crystal was a perfect single crystal preferentially orienting in the (110) direction and met the basic demand of its applications.

Multiple Interfacial Fe3O4@BaTiO3/P(VDF-HFP) Core-Shell-Matrix Films with Internal Barrier Layer Capacitor (IBLC) Effects and High Energy Storage Density

Flexible nanocomposites composed of high dielectric constant fillers and polymer matrix have shown great potential for electrostatic capacitors and energy storage applications. To obtain the composited material with high dielectric constant and high breakdown strength, multi-interfacial composited particles, which composed of conductive cores and insulating shells and possessed the internal barrier layer capacitor (IBLC) effect, were adopted as fillers. Thus, Fe3O4@BaTiO3 core-shell particles were prepared and loaded into the poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) polymer matrix. As the mass fraction of core-shell fillers increased from 2.5 wt % to 30 wt %, the dielectric constant of the films increased, while the loss tangent remained at a low level (<0.05 at 1 kHz). Both high electric displacement and high electric breakdown strength were achieved in the films with 10 wt % core-shell fillers loaded. The maximum energy storage density of 7.018 J/cm3 was measured at 2350 kV/cm, which shows significant enhancement than those of the pure P(VDF-HFP) films and analogous composited films with converse insulating-conductive core-shell fillers. A Maxwell-Wagner capacitor model was also adopted to interpret the efficiency of IBLC effects on the suppressed loss tangent and the superior breakdown strength. This work explored an effective approach to prepare dielectric nanocomposites for energy storage applications experimentally and theoretically.

Influence of ferroelectric-electrode interfaces on the electrical properties of BaTiO 3 -CoFe 2 O 4 magnetoelectric composites

In order to further investigate the influence of electrode types and preparation conditions on the electrical properties of magnetoelectric (ME) composite ceramics, layered BaTiO3-CoFe2O4 (BTO–CFO) composites were prepared using tape casting method, and the effects of silver and aluminium electrodes on the electrical properties were studied. It is found that the different electrical properties of the ME composites are related to the ferroelectric-silver and ferroelectric-aluminium interfaces formed at the same annealing temperature, in which the former enhance the leakage current density, dielectric properties and AC conductivity, but lower the ferroelectric properties compared to the latter. Meanwhile, the electrical properties of the composite, especially leakage current and ferroelectric properties, are influenced by the silver electrode annealing temperature. In addition, space charges and polarons are responsible for the dielectric constant and AC conductivity of the ME composites, respectively.

Simulation of wireless passive SAW sensors based on FEM/BEM model

Research on the wireless passive surface acoustic wave (SAW) impedance-loaded sensors has received significant attention in recent years. This paper concentrates on the simulation method of these sensors. In our previous work, the coupling-of-modes (COM) model of impedance-loaded SAW sensors was constructed based on the models of SAW IDT. The accuracy of this model depends on the accuracy of their parameters. A numerical combined finite element method and boundary element method (FEM/BEM) model was used to derive COM parameters more accurately in this paper. We used a finite element method to account for the mass loading effect of electrodes and use a Greens function to model the piezoelectric substrate. Comparison between simulations and measurements on real SAW devices shows good agreement and proofs the effectiveness of this simulation method.

Structural evolution and physical properties of multiferroic Bi0.9−x La0.1Pb x FeO3−x/2 ceramics

The polycrystalline samples of multiferroic Bi0.9−x La0.1Pb x FeO3−x/2 (x = 0–0.35) were prepared by the solid state reaction method and characterized by x-ray diffraction, field emission scanning electron microscopy, dielectric, magnetic, magnetodielectric (MD) and magnetoelectric (ME) measurements. A structural evolution from rhombohedral to pseudocubic structure was found to happen near x = 0.20. The changes and anomalies observed in magnetization were correlated with structural evolution and the development in microstructure. The ferroelectromagnetic measurements demonstrated Pb2+ doping to be a very effective method to realize the coexistence of weak ferromagnetism and ferroelectric in the ferroelectric R3c phase of BiFeO3. The MD and ME effects of Bi0.9−x La0.1Pb x FeO3−x/2 ceramics were first reported. A maximum ME voltage coefficient has been observed at x = 0.30. This work is helpful for understanding the ferroelectromagnetic behaviors and ME effect with complicated spin structures.

Large magneto-electric effects in hexagonal La0.7Ba0.3MnO3-BaTiO3 solid solutions and magneto-electric coupling mechanism discussion

The solid solutions of La0.7Ba0.3MnO3-BaTiO3 were first prepared by a solid state method. The XRD showed that the solid solutions formed when the BaTiO3 transformed from tetragonal to hexagonal phase with sintering temperature increasing. The samples with hexagonal phase exhibited relative large magneto-electric effects. For the sample sintered at 1475 °C, the measured maximum magneto-electric coefficient was 48.6 mV/cmOe, obtained at a frequency of 30 kHz. The first-principles calculations indicated that the magnetic-electric coupling was attributed to the off-centering of Mn ions in coplanar octahedrons in the hexagonal phase. The present results suggest a new candidate for a room temperature multiferroic material with magneto-electric effects.

Progress of matching network for passive remote hybrid sensor based on SAW resonator

The matching network is an important section of the passive remote SAWR (surface acoustic wave resonator) hybrid sensor. There were two disadvantages for the classical method to design the matching network: The one was that the matching network reduces the Q factor of match point. The other was the strong mismatch occurs when the impedance of sensing element shifted from the well-matched point. S. Klett et al proposed the well-matched matching network, and improved the Q of match point. This paper researched the low-mismatched matching network deeply.