Structural and thermoelectric properties of hydrothermal-processed Ag-doped Fe2O3

Fe_2-xAg_xO₃ (0?≤?x?≤?0.04) nanopowders with various Ag contents were synthesized at different hydrothermal reaction temperatures (150?°C and 180?°C). Their structural properties were fully investigated through an X-ray diffraction, a Fourier transform infrared spectroscopy, and an X-ray photoelectron spectroscopy. The hydrothermal reaction temperature, time, and Ag content remarkably affected the morphological characteristics and crystal structure of the synthesized powders. The Fe_2-xAg_xO₃ (0?≤?x?≤?0.04) powders synthesized at 150?°C for 6?h and the Fe_2-xAg_xO₃ (0.02?≤?x?≤?0.04) powders synthesized at 180?°C for 12?h formed the orthorhombic α-FeOOH phase with a rod-like morphology, whereas the Fe_2-xAg_xO₃ (0?≤?x?≤?0.01) powders synthesized at 180?°C for 12?h formed the rhombohedral α-Fe₂O₃ phase with a spherical-like morphology. The Fe_1.98Ag_0.02O₃ fabricated by utilizing Fe_1.98Ag_0.02O₃ powders synthesized at 180?°C showed the largest power factor (0.64?×10^?5 Wm^?1 K^?2) and dimensionless figure-of-merit (0.0036) at 800?°C.     

High performance multi-layer varistor (MLV) from doped ZnO nanopowders by water based tape casting: Rheology,sintering, microstructure and properties

In this work, we report the fabrication of a high performance multi-layer varistor (MLV) via water based tape casting method using novel compositions of nanomaterials. Bi₂O₃, CaO and Co₃O₄ doped ZnO nanopowders were prepared by solution combustion synthesis (SCS) route, calcined at different temperatures (550, 650, 750 and 850?°C) and characterized by TEM, XRD, SEM and AFM. The nanopowder (crystallite size ~30?nm) calcined at 650?°C for 1?h was used as the starting material for MLV fabrication. Compositions of the slurry containing doped ZnO nanopowders, binder and plasticizer in water solvent were optimized for the fabrication of thick film. The rheological properties of the slurries having different solid loadings were analysed and thick films of various thicknesses (50–500?µm) were prepared by varying the feeding rate of tape casting. The film roughness of 38.3?nm for the thick film made from 40?wt% solid slurry was found to be superior compared to other samples due to the presence of reduced crack and shrinkage. MLV fired at 950?°C for 1.5?h exhibited a coefficient of nonlinearity of 18 and breakdown voltage of 291.5?V that yields superior properties compared to commercial MLVs.     

Effect of donor W and acceptor Ni codoping at Ti site on the structure and electrical properties of Na0.5Bi0.5TiO3 thin film

Pure Na_0.5Bi_0.5TiO₃ (NBT), donor W⁶⁺ doped NBT (NBTW), acceptor Ni²⁺ doped NBT (NBTNi), as well as donor W⁶⁺ and acceptor Ni²⁺ codoped NBT (NBTWNi) polycrystalline films are fabricated on indium tin oxide (ITO)/glass substrates via a chemical solution deposition method. The roles of aliovalent-ion substitution on the crystallinity, ferroelectric and dielectric properties of NBT film are mainly investigated. With the introduction of aliovalent-ion, the surface of the doped film becomes more uniform and the leakage current is reduced. Well saturated polarization-electric field (P-E) loops can be observed in W⁶⁺ and Ni²⁺ codoped NBT film due to its lowest leakage currents compared to those of other films. Also, the effect of voltage and frequency on the capacitance-voltage (C-V) curve and the dielectric tunability for the NBTWNi film is discussed. The ferroelectric and dielectric properties are largely improved in NBTWNi film, which can be ascribed to the synergetic effect of high-valence W⁶⁺ and low-valence Ni²⁺ ions. The cooperation between the acceptor and donor cations can effectively eliminate the mobile oxygen vacancies in NBT films.     

Improved physical properties of Al-doped ZnO thin films deposited by unbalanced RF magnetron sputtering

Room temperature Al-doped ZnO (AZO) thin films with improved crystalline and optical properties were grown on normal glass substrates using unbalanced RF magnetron sputtering technique. To modify the plasma density towards the substrate and enhance the crystalline nature, an additional magnetic field ranging from 0 to 6.0 mT has been applied to the AZO target by proper tuning of solenoid coil current from 0 to 0.2 A respectively, which plays a significant role for controlling the physical properties of AZO films. The results from XRD studies indicate that all AZO films were composed of hexagonal wurtzite structure with better crystal quality through the applied magnetic field, ZnO (002) plane as a preferred growth. Furthermore, XPS studies suggested that symmetric chemical shifts in the binding energies for the Zn 2p and O1s levels with applied magnetic field. SEM analysis revealed the formation of a smooth, homogeneous and dense morphological surface with applied magnetic field. From AFM analysis, it was observed that the applied magnetic field strongly influenced the grain size and the films showed decreasing tendency in electrical resistivity. Films exhibited superior optical transmittance more than 94% in the visible region essentially due to the formation of better crystalline nature. The results indicate that improved band gap from 3.10 to 3.15 eV with additional magnetic field varied from 0 to 6.0 mT respectively.     

Structural and electrical properties of lead free ceramic: Ba(La1/2Nb1/2)O3

Abstract

Abstract

Lead free perovskite Ba(La_1/2Nb_1/2)O₃ was prepared by conventional ceramic fabrication technique at 1375°C for 7?h in air atmosphere. The crystal symmetry, space group and unit cell dimensions were estimated using Rietveld analysis. X-ray diffraction analysis indicated the formation of a single phase monoclinic structure with space group P2/m. Energy dispersive X-ray analysis and scanning electron microscopy studies were carried to study the quality and purity of the compound. Permittivity data showed low temperature coefficient of capacitance (T _CC = 11%) up to 100°C. The circuit model fittings were carried out using the impedance data to find the correlation between the response of real system and idealised model electrical circuit. Complex impedance analyses suggested the dielectric relaxation to be of non-Debye type. The correlated barrier hopping model was employed to successfully explain the mechanism of charge transport in Ba(La_1/2Nb_1/2)O₃. The AC conductivity data were used to evaluate the density of states at Fermi level, minimum hopping length and apparent activation energy.     

Negative thermal expansion,electrical and mechanical properties of antiperovskite Mn3Zn0.5A0.5N (A = Sn,Ag, Ni)

Thermal expansion, electrical conductivity, hardness and friction property of Mn₃ZnN, which had been doped with Sn, Ag or Ni and sintered at 1223?K, were measured. X-ray diffraction analyses show that these compounds have a cubic antiperovskite Mn₃CuN-type structure and negative thermal expansion (NTE). The width of NTE operation temperature (ΔT) and the coefficient of thermal expansion are different when Mn₃ZnN was doped with different element. A giant NTE coefficient of ?81.00?×?10^?6?K^?1 is obtained from Mn₃Zn_0.5Ag_0.5N while ΔT is 18?K. A broad ΔT of 60?K is obtained from Mn₃Zn_0.5Sn_0.5N with thermal expansion coefficient of ?19.05?×?10^?6?K^?1. The results show that Mn₃Zn_0.5 A_0.5N (A?=?Sn, Ag, Ni) has good electrical conductivity. The electrical conductivity of Mn₃Zn_0.5Ag_0.5N is the largest among these compounds as 2.45?×?10³?S?cm^?1. The Vickers hardness of these compounds is more than 350?HV. The friction coefficients of Mn₃Zn_0.5Ag_0.5N, Mn₃Zn_0.5Ni_0.5N and Mn₃Zn_0.5Sn_0.5N are 0.5318, 0.4554 and 0.2336, respectively.     

Mechanical and electrical properties of MoSi2–RSiC composites via a combination of phenolic resin infiltration–pyrolysis and MoSi2–Si–Ti alloy-activated melting infiltration composite processes

A three-dimensional interpenetrated network structure composite was designed and prepared via a combination of phenolic resin infiltration-pyrolysis and MoSi₂–Si–Ti alloy-activated melting infiltration processes to effectively merge the desirable properties of MoSi₂ and RSiC. Influence of infiltration temperature on the microstructure, mechanical and electrical properties of the composites was examined. Almost dense MoSi₂–RSiC composites with the designed structure were obtained at 1900°C. Formation of the gradient interface modified the interface combination and enhanced the mechanical and electrical properties of the composite. Flexural strength of the composites reached approximately 114.262?MPa (room temperature) and 128.392?MPa (1400°C), respectively, indicating corresponding increases of 37.08 and 35.69% compared with the RSiC matrix. Volume resistivity decreased to 57.63?mΩ?cm, nearly five orders of magnitude lower than that of RSiC. Influence of the interpenetrated network structure and interface combination on the electrical conductivity behaviour of the composites was discussed via a modified mixture rule.     

Lu3+/Yb3+ and Lu3+/Er3+ co-doped antimony selenide nanomaterials: synthesis,characterization, and electrical,thermoelectrical, and optical properties

Lu³⁺/Yb³⁺ and Lu³⁺/Er³⁺ co-doped Sb₂Se₃ nanomaterials were synthesized by co-reduction method in hydrothermal condition. Powder X-ray diffraction patterns indicate that the Ln_xLn^′_xSb_2−2xSe₃ Ln: Lu³⁺/Yb³⁺ and Lu³⁺/Er³⁺ crystals (x = 0.00 − 0.04) are isostructural with Sb₂Se₃. The cell parameters were increased for compounds upon increasing the dopant content (x). Scanning electron microscopy and transmission electron microscopy images show that co-doping of Lu³⁺/Yb³⁺ ions in the lattice of Sb₂Se₃ produces nanorods, while that in Lu³⁺/Er³⁺ produces nanoparticles, respectively. The electrical conductivity of co-doped Sb₂Se₃ is higher than that of the pure Sb₂Se₃ and increases with temperature. By increasing the concentration of Ln³⁺ions, the absorption spectrum of Sb₂Se₃ shows red shifts and some intensity changes. In addition to the characteristic red emission peaks of Sb₂Se₃, emission spectra of co-doped materials show other emission bands originating from f-f transitions of the Yb³⁺ ions.     

气体绝缘金属封闭开关设备的漏气处理

气体绝缘金属封闭开关设备(GIS)气体泄漏是其一个主要缺陷。在对青岛供电公司GIS的漏气处理工作进行现场调查分析的基础上,针对引起设备漏气及漏气处理不成功的主要原因,提出了对漏气处理工作的改进措施,经现场应用青岛供电公司GIS漏气处理成功率由92%提升到98%。     

A new method to improve the electrical properties of KNN-based ceramics: Tailoring phase fraction

Although both the phase type and fraction of multi-phase coexistence can affect the electrical properties of (K,Na)NbO₃ (KNN)-based ceramics, effects of phase fraction on their electrical properties were few concerned. In this work, through changing the calcination temperature of CaZrO₃ powders, we successfully developed the 0.96 K_0.5Na_0.5Nb_0.96Sb_0.04O₃-0.01CaZrO₃-0.03Bi_0.5Na_0.5HfO₃ ceramics containing a wide rhombohedral-tetragonal (R-T) phase coexistence with the variations of T (or R) phase fractions. It was found that higher T phase fraction can warrant a larger piezoelectric constant (d₃₃) and d₃₃ also showed a linear variation with respect to tetragonality ratio (c/a). More importantly, a number of domain patterns were observed due to high T phase fraction and large c/a ratio, greatly benefiting the piezoelectricity. In addition, the improved ferroelectric fatigue behavior and thermal stability were also shown in the ceramics containing high T phase fraction. Therefore, this work can bring a new viewpoint into the physical mechanism of KNN-based ceramics behind R-T phase coexistence.