Zhiping Zheng

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.

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.

Preparation and effects of glass-coatings on BaTiO3-based PTC thermistors

AbstractGlasses in the Na2O–K2O–K2SiF6–ZnO–Al2O3–B2O3–SiO2 system were investigated as potential intermediate temperature sealing materials to protect BaTiO3-based positive temperature coefficient (PTC) thermistors. The influence of compositional changes on the crystallization tendency and sintering behavior of the glass was reported. Additionally, the electrical properties of PTC thermistors with glass-coatings were compared with those without glass-coatings. The results showed that the formulation (in wt%), 3.1Na2O–9.4K2O–10.6K2SiF6–4.3ZnO–4.3Al2O3–20.3B2O3–48SiO2 (G2), performed better on thermal properties, had a good glass formability within a relatively wide range of sintering temperature and was compatible with the PTC thermistors (no cracks or pinholes). Furthermore, the glass layer did not affect the characteristics of the PTC thermistors too much.

Preparation of BaTiO3-based chip thermistors by gelcasting approach

Abstract Gelcasting has been developed as a novel ceramic forming method for complex-shaped advanced materials of near-net-shape. In this work, the gelcasting process has been further developed to fabricate BaTiO 3 -based positive temperature coefficient chip thermistor. Special attentions were given to the effect of atmosphere type on gelcasting behavior of ceramics and the effect of the presence of glycerol and monomers in slurries on the flexibility and mechanical strength of gelcast green sheets. Compared with roll formed thermistors, gelcast ones exhibit stronger PTC effect.

Exceptional co-catalyst free photocatalytic activities of B and Fe co-doped SrTiO 3 for CO 2 conversion and H 2 evolution

CO2 should be converted into chemical-fuels, and to reduce H2O to H2 over SrTiO3 (STO) owing to its negative conduction band position vs. NHE. Herein a novel B and Fe co-doped SrTiO3 (B, F-STO) photocatalyst was successfully fabricated via a single-step sol-hydrothermal process. Various experiments confirmed that B and Fe are effectively doped into the STO matrix. Boron substituted oxygen anions, while Fe substituted Ti cations. UV–visible diffuse reflectance spectra (UV–vis DRS) and valence-band X-ray photoelectron spectroscopy (XPS) spectra confirmed that the band gap of STO significantly reduced from 3.4 to 1.9 eV upon co-doping with B and Fe. Hence, the B, F-STO photocatalyst exhibits more absorption (λ ≤ 650 nm) compared to pure STO (λ ≤ 360 nm). Further, from photoluminescence spectra, fluorescence spectra, and photoelectrochemical measurements, charge separation in STO is considerably enhanced by co-doping B and Fe. This resulted in the improved UV–vis light catalytic activities for CO2 conversion to CH4 and CO and H2O splitting to evolve H2. The amounts of CH4 and CO produced over B, F-STO are ∼ 17.2 and 21 μmol, respectively, about 5-fold enhanced compared to that of STO (∼ 3.4 μmol CH4 and 5.2 μmol CO), and the calculated quantum efficiency at λ = 420 nm is ∼ 2.16%. Similarly, the amount of H2 produced over B, F-STO is ∼ 61 μmol, about 6.7-fold enhanced compared to that over STO (9 μmol), and the calculated quantum efficiency at λ = 420 nm is ∼ 2.12%. This work provides feasible routes to fabricate highly efficient SrTiO3-based nanophotocatalysts for solar-fuel production.

Al-doped ZnO varistors prepared by a two-step doping process

ABSTRACT It is difficult to dope Al into main grains of ZnO varistor ceramics, especially for small doping amount. Generally, all raw materials including Al dopant are directly mixed together and sintered into ceramics. However, in this direct doping process, Al is apt to stay in grain boundaries, and almost does not enter grains. This does harm to the electrical properties of ZnO varistors. In this paper, we proposed a two-step doping process. Al2O3 powder was first mixed only with a part of the ZnO powder and pre-sintered. The pre-sintered powder was mixed with other additives such as Bi2O3 and the rest ZnO. Then ZnO varistor ceramics were prepared via solid state sintering processes. Results showed that two-step doped ZnO varistors exhibited improved electrical properties with a significant increased nonlinear coefficient and a great decreased leakage current compared to directly doped ones because more Al was incorporated into ZnO grains.