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In this work, ZnO–Bi2O3 based low-voltage varistors were prepared by co-doping of In2O3 and Ta2O5, which achieved a high nonlinear coefficient with a low breakdown voltage. By exploring the microstructure and electrical performance of the samples, it was found that the samples co-doped with In2O3 and Ta2O5 have uniform microstructure, and the threshold voltage decreased slightly while the leakage current decreased. The best performance of the varistor was obtained at 0.15 mol% Ta2O5 doping with a breakdown voltage of 184 V/mm, a nonlinear coefficient of 32.3 and a leakage current of 0.04 μA. The grain boundary resistance of the varistor increased after the co-doping of In2O3 and Ta2O5, which was conducive to improving performance stability of the sample. All varistors could be aged, but the parameter change rate of doped varistors was significantly smaller. [ABSTRACT FROM AUTHOR]

With the development trend of device miniaturization, the demand for varistor ceramics with high break field is becoming more and more important. To enhance the high-voltage performance and improve the nonlinear coefficient of zinc oxide varistor ceramics, the technical advantages of rare earth and flash sintering were innovatively proposed to effectively improve the varistor performance, and their microstructure and electrical properties were systematically studied. The results indicate that rare earth doping affected the formation of liquid phase and thus reduced the electrical conductivity during flash sintering, which decreased the conductivity in the early stage of flash sintering. Moreover, the pinning effect from rare earth doping to ZnO grains inhibited grain growth, which leads to a smaller grain size. The breakdown field of 0.2 mol % Y2O3 + 0.2 mol % Sc2O3 composite doped sample has been significantly improved to 1880 V/mm, with a nonlinear coefficient of 42.5 and the leakage current of 0.5 μA. It also exhibits a high dielectric constant of 267 on 1 kHz, and better dielectric frequency stability compared to others. [ABSTRACT FROM AUTHOR]

The crystal phase combination, relative density, microstructure, varistor properties and dielectric properties of La2O3-doped ZnO-Bi2O3-based varistor at a furnace temperature of 950 °C were investigated under the electric field of 300 V/cm within 35 s. Obtained samples were fully densified and uniform in microstructure. The effect of doping with different contents of La2O3 on flash-sintered ZnO-Bi2O3-based varistor was systematically studied. The results showed that when doping La2O3 was 0 mol%, 0.1 mol%, 0.2 mol% and 0.3 mol%, the densities of the samples were 91.5%, 90.5%, 96.1% and 95.1%, respectively. When the La2O3 doping amount was 0.2 mol%, the nonlinear coefficient was the highest of 32.9, the leakage current was the lowest of 1.1μA, and the dielectric loss was less than 0.1. Therefore, uniform microstructure and excellent electrical property can be obtained by preparing La2O3-doped ZnO varistor ceramic via flash sintering. [ABSTRACT FROM AUTHOR]

The continuous development of microelectronic devices with integrated functions has led to an increasing interest in the development of dielectric ceramics with high dielectric constant, low dielectric loss, good frequency, and temperature stability. In this work, (Ca, Sb)-co-doped TiO2 (CSTO) ceramics were prepared by solid-phase reaction sintering method and their phase structure, microstructure, giant dielectric properties, and mechanism were systematically investigated. The results show that the secondary phase of CSTO ceramic samples appeared when x ≥ 4%. The average grain size of CSTO ceramics decreased as the amount of doping increases, and all CSTO ceramics had giant dielectric constants. When the doping amount was x = 4%, the CSTO ceramics obtained optimum dielectric properties, where ε′ = 2.6 × 105 and tan δ = 0.10. X-ray photoelectron spectroscopy (XPS) results showed that the giant dielectric origin was mainly due to the Sb5+ doping that generated electrons inside the material, Ca2+ doping that enhanced the generation of vacancies inside the material, and the defective dipole clusters produced that improved the dielectric properties of the CSTO ceramics. This work is critical for the development and deployment of new TiO2-based giant dielectric ceramics. [ABSTRACT FROM AUTHOR]

The dense bulk ZnO–Bi2O3–Co2O3 varistor ceramics were obtained via flash sintering. The effect of electric field on densification, microstructure, and electrical properties of ZnO–Bi2O3-based varistor ceramics, which were under different electric fields by a constant heating flash sintering process was investigated. The results showed that when the electric field was increased from 200 to 350 V/cm, the onset temperature of flash sintering decreased significantly, and the peak power consumption increased. The flash-sintered specimen under the electric field of 200 V/cm at a furnace temperature of 762 °C obtained the highest nonlinear coefficient of 41.1 and the lowest leakage current of 1.57 μA. [ABSTRACT FROM AUTHOR]

In this paper, (Al, Ta) co-doped TiO2 (ATTO) ceramics were successfully prepared by flash sintering method under different electric fields (450–650 V/cm). The effects of electric field on flash sintering behavior, phase structure, microstructure, dielectric properties and varistor properties of ATTO ceramics were systematically studied. The results showed that all flash sintering ATTO ceramics were single rutile structure. With increasing electric field, grain size gradually increased. When the electric field was 550 V/cm, ATTO ceramic had the best comprehensive performance with dielectric constant of approximately 1.7 × 104, dielectric loss of about 0.5 at 1 kHz, and nonlinear coefficient of 3.5. X-ray photoelectron spectroscopy (XPS) and Impedance spectra (IS) results showed that the origin of good dielectric property was attributed to the internal barrier layer capacitance effect. Therefore, this work is not only of great significance to the further study of co-doped TiO2 colossal dielectric ceramics, but also offers an excellent method for the preparation of capacitive varistor dual-function ceramics. [ABSTRACT FROM AUTHOR]

Injection-compression-compression (I-C-C) process was studied to prepare polypropylene/ short carbon fiber (PP/SCF) composites. The effects of I-C-C process on the conductive network, fiber distribution and electric conductivity were investigated. The distance between conductive particles of the blending system was reduced by two-stage compression, so that the conductive network was compacted. The forming of dense conductive network significantly improved the conductivity. Moreover, I-C-C can effectively interfere with the fiber flow direction to enhance the conductivity of the infiltrated surface. Combined with the microstructure and electrical conductivity, the applicable mold temperature and compression speed range of the I-C-C process for PP can be obtained. The results showed that the electrical conductivity of the I-C-C prepared PP/SCF was increased up to 5 orders of magnitude higher than that of ordinary injection molding. Conductivity of PP/ 10 wt% SCF conductivity reached 3.7S/m, PP /15 wt% SCF reached 33S/m, and PP/ 20% SCF reached 150S/m. [ABSTRACT FROM AUTHOR]

The mobility disparity between oil and water accounted for the poor water swept efficiency. Previous research has testified that nitrogen foam can increase sweep area and control water and gas mobility. However, the former studies have largely covered the mobility control ability performance in some conventional reservoir rather than that under high temperature and high salinity. This paper presents the results of a laboratory study of nitrogen foam at the experimental condition (113 °C and 21.28 × 104 mg/L) on its mobility control ability investigation, including different gas-to-liquid ratio, injection rate and core permeability; additionally, a novel method on studying the stability of mobility control ability of foam was utilized. Nitrogen foam injection was conducted in core holder to investigate the shape discrepancy of each resistance factor and residual resistance curve. The results showed that the most moderate gas-to-liquid ratio and injection rate were 2:1 and 1 mL/min, respectively; foam performed more significant mobility control ability with the increase in permeability. After 5 days’ aging, nitrogen foam still got enough mobility control ability to block water channeling. The above results demonstrate that, under high temperature and high salinity condition, nitrogen foam still can act as a promising economical method for improving the mobility difference between water and oil by applying appropriate injection parameters. [ABSTRACT FROM AUTHOR]