Nonlinear electrical properties and aging characteristics of (NiO, MgO, Cr2O3)-doped Zn-Pr-Co-R (R = Y, Er) oxide-based varistors

The electrical properties and stability of the varistors, which composed of (NiO, MgO, Cr₂O₃)-doped Zn-Pr-Co-R (Y, Er) oxide-based ceramics, were investigated for different additives. The breakdown voltage of the varistors increased in order of NiO→undoped→MgO→Cr₂O₃: 1200→1551→1691→1959 V/cm for ZPCY system and undoped→NiO→MgO→Cr₂O₃: 1024→1041→1500→1668 V/cm for ZPCE system, respectively. The nonlinear coefficient value increased in order of undoped→NiO→MgO→Cr₂O₃: 21→25→38→50 in ZPCY system and NiO→undoped→MgO→Cr₂O₃: 27→32→35→38 in ZPCE system, respectively. In ZPCY and ZPCE systems, the Cr₂O₃-additives most greatly improved the nonlinear properties. In Cr₂O₃-doped system, ZPCY system exhibited higher nonlinear properties than that of ZPCE system. The stability against d.c. accelerated aging stress was higher in Cr₂O₃-additives than in NiO- and MgO-additives for ZPCY system and was higher in NiO-additives than in MgO- and Cr₂O₃-additives for ZPCE system.     

Cr2O3对(Co,Ta)掺杂的SnO2压敏电阻电学特性的影响

研究了Cr对(Co,Ta)掺杂的SnO2压敏材料电学性质的影响.当Cr2O3的含量从0增加到0.15mol%时,(Co,Ta)掺杂SnO2压敏电阻的击穿电压从206V/mm增加到493V/mm;1kHz时的相对介电常数从1968猛降至498;晶界势垒高度分析表明,SnO2晶粒尺寸的迅速减小是样品击穿电压增高、相对介电常数急剧降低和电阻率迅速增大的主要原因.对Cr含量增加引起SnO2晶粒减小的原因进行了解释.掺杂0.15mol% Cr2O3的SnO2压敏电阻非线性系数为24,击穿电压达498V/mm,在高压保护领域有很好的应用前景.     

Effect of Er2O3 addition on the microstructure, electrical properties, and stability of Pr6O11-based ZnO ceramic varistors

The microstructure, electrical properties, and stability of Pr₆O₁₁-based ZnO varistors, which are composed of ZnO-Pr₆O₁₁-CoO-Er₂O₃ systems, were investigated with Er₂O₃ additive content. The density of ceramics was in the range of 84–88% of TD at 1300 °C and 93–98% of TD at 1350 °C, and greatly affected the stability. Most of the added-Er₂O₃ were segregated at nodal points. The varistors with 0.5 mol% Er₂O₃ sintered at 1300 °C exhibited the best nonlinear current-voltage characteristics, which the nonlinear exponent is 52.8 and the leakage current is 9.8 A. All the varistors sintered at 1300 °C, even under relatively weak stress, exhibited the thermal runaway within short time in order of high leakage current. On the contrary, the stability of varistors sintered at 1350 °C exhibited far higher stability than that at 1300 °C. Particularly, the varistors with 0.5 mol% Er₂O₃ exhibited not only relatively good nonlinear current-voltage characteristics, which the nonlinear exponent is 34.8 and the leakage current is 7.4 A, but also excellent stability, which the variation rates of varistor voltage, nonlinear exponent, and leakage current are below 1%, 3%, and 3%, respectively, even under more severe stress such as (0.80 V _{1 mA}/90 °C/12 h) + (0.85 V _{1 mA}/115 °C/12 h) + (0.90 V _{1 mA}/120 °C/12 h).     

Effect of sintering temperature on electrical properties and stability of Pr6O11-based ZnO varistors

The electrical properties and stability of ZPCCE varistors, which are composed of ZnO-Pr₆O₁₁-CoO-Cr₂O₃-Er₂O₃-based ceramics, were investigated as a function of sintering temperature and time in the range of 1325–1345 °C for 1–2 h. As the sintering temperature and time increased the nonlinear exponent decreased, whereas the leakage current was improved, and overall, its stability was also improved. Among all ZPCCE-based varistors, the varistors sintered at 1335 °C for 1 h exhibited the highest nonlinearity, with a nonlinear exponent of 70.53 and a leakage current of 1.92 A, but revealed comparatively low stability. The varistors sintered at 1340 °C for 2 h, with a nonlinear exponent of 43.37 and a leakage current of 1.18 A, exhibited the highest stability, in which the variation rates of the varistor voltage, nonlinear exponent, leakage current were –1.54%, –2.49%, and +240.68%, respectively, under continuous DC stress, such as . These varistors will be usefully applied to surge protectors in the future. Conclusively, it was found that the electrical properties and stability of ZPCCE varistors are strongly affected by the sintering temperature and time.     

Effect of sintering time on electrical characteristics and DC accelerated aging behaviors of Zn-Pr-Co-Cr-Dy oxide-based varistors

The electrical properties and DC accelerated aging behaviors for nonlinear properties and dielectric characteristics of the varistors, which are composed of ZnO–Pr₆O₁₁CoO–Cr₂O₃–Dy₂O₃ (ZPCCD)-based ceramics, were investigated for different sintering times. The increase of sintering time deteriorated nonlineacy by decreasing a nonlinear exponent from 66.6 to. 46.5 and increasing a leakage current from 1.2 to 3.5 μA. But, the appropriate sintering time decreased a dissipation factor and improved the DC accelerated aging characteristics. The varistors sintered for 2 h exhibited not only relatively high nonlinearity, with the nonlinear exponent of 54.8, the leakage current of 2.5 μA, and dissipation factor of 0.0263 but also the highest stability, in which the variation rates of varistor voltage, nonlinear exponent, leakage current, and dissipation factor are ?1.19%, ?4.0%, +75.8%, and +43.8%, respectively. As sintering time increases, the donor concentration and density of interface states increased in the range of 1.08 × 10¹⁸–1.48× 10¹⁸/cm³ and 3.40 × 10¹²–3.86 × 10¹²/cm², respectively. However the barrier height increased with increasing sintering time.     

Al doping effect on microstructure, electrical properties, dielectric characteristics, and aging behaviors of ZPCCY-based varistors

The Al doping effect on the microstructure, electrical properties, dielectric characteristics, and aging behaviors of ZPCCY-based varistors was investigated in the range of 0.0–0.1 mol%. The breakdown electric field in the E-J characteristics decreased in a wide range from 4,921 to 475 V/cm with increasing amounts of Al₂O₃. The nonlinear properties were improved by increasing amounts of Al₂O₃ up to 0.005 mol%, whereas the further additions caused it to decrease. The highest nonlinear coefficient (α = 45.2) was obtained when Al₂O₃ concentration is 0.005 mol%. The Al₂O₃ acted as a donor due to the increase of electron concentration in the small range of 0.0–0.1 mol%. On the other hand, an appropriate addition of Al₂O₃ in the range of 0.001–0.005 mol% was found to significantly improve the electrical stability against DC accelerated aging stress.     

Effect of aluminum doping on electrical and dielectric aging behavior against current impulse of ZPCCY-based varistors

The electrical and dielectric aging behavior against current impulse (5–1,200 A) in the Zn-Pr-Co-Cr-Y-based varistors was investigated with aluminum doping level (0–0.01 mol%). The varistors doped with 0–0.001 mol% Al were destroyed at higher current impulse beyond 900 A and the varistors doped with 0.005–0.01 mol% Al exhibited high stability against current impulse. The clamp ratio (K) at given current impulse ranges decreased with increasing Al doping level. The varistor doped with 0.01 mol% Al exhibited the lowest K value, with 1.65 at a current impulse of 10 A and 2.38 at a current impulse of 1,200 A. The best electrical and dielectric stability against current impulse of 1,200 A was obtained at 0.01 mol% Al, where %\Updelta E_{1  \textmA/cm²} = -3.4%\%\Updelta E_{1\;\text{mA/cm}^2} = -3.4\%, %Δα = 0%, %ΔJ _L = −26.3%, %Δε′_APP = +3.4%, and %Δtanδ = −7.7%. Conclusively, Al doping level was optimized at 0.01 mol% in terms of the surge withstand capability (SWC).     

The effect of sintering temperature on varistor properties of (Pr, Co, Cr, Y, Al)-doped ZnO ceramics

The effect of sintering temperature on varistor properties of (Pr, Co, Cr, Y, Al)-doped ZnO ceramics was investigated in the range of 1280-1350 °C. The increase of sintering temperature increased the average grain size (4.8-12.9 μm), whereas the sintered density was not nearly affected by sintering temperature. The breakdown field decreased over a wide range from 4610 to 1513 V/cm with the increase of sintering temperature. The nonlinear coefficient of this system was nearly constant in the range of 44-47 regardless of sintering temperature. The donor density decreased in the range of 1.51-1.32 × 10¹⁸/cm³ and the barrier height decreased from 1.40 to 0.92 eV with the increase of sintering temperature.     

Microstructure, electrical properties, and degradation behavior of praseodymium oxides-based zinc oxide varistors doped with Y2O3

The microstructure, electrical properties, and degradation behavior of Pr-based zinc oxide varistors, which are composed of Zn-Pr-Co-Cr-Y oxides were investigated according to Y₂O₃ additive content in the range 0.5–4.0 mol%. The majority of the Sadded Y₂O₃ were segregated at the multiple ZnO grain junctions and grain boundaries. The average grain size was markedly decreased in the range 27.3–8.6 m with increasing Y₂O₃ additive content. Y₂O₃ acted as an inhibitor of grain growth. Additions of Y₂O₃ increased the varistor voltage in the range 36.90–686.58 V/mm, increased the nonlinear exponent in the range 3.75–87.42, decreased the leakage current in the range 115.48–0.047A, increased the barrier height in the range 1.06–2.16 eV, and decreased the donor concentration in the rang 1.87 × 10¹⁸–0.19 × 10¹⁸ cm^–3. Y₂O₃ acted as an acceptor, as a result of the decrease of donor concentration. All Pr-based ZnO varistors doped with Y₂O₃ exhibited very predominant degradation characteristics, which show a nearly symmetric I-V after the stress. In particular, since 4.0 mol% Y₂O₃-added ZnO varistor has not only very excellent non-ohmicity, but also very stable degradation behavior, it is estimated to be sufficiently used to various application fields.     

Microstructure and electrical properties of (Ta, Co, Pr) doped TiO2 based electroceramics

The addition of different dopants affects the densification, mean grain size and electrical properties of TiO₂-based varistor ceramics. This paper discusses the microstructural and electrical properties of (Ta, Co, Pr) doped TiO₂ systems, demonstrating that some of these systems display electrical properties that allow for their use as low voltage varistor. Dopants such as Ta₂O₅ play a special role in the formation of barriers at the grain boundary and in the nonlinear behavior in TiO₂-based systems. The higher values of nonlinear coefficient and breakdown electric field were obtained in the system just doped with Ta₂O₅ and CoO.     

Effect of aluminum oxide doping on the structural,electrical, and optical properties of zinc oxide (AOZO) nanofibers synthesized by electrospinning

Zinc oxide nanofibers doped with aluminum oxide were prepared by sol–gel processing and electrospinning techniques using polyvinylpyrrolidone (PVP), zinc acetate and aluminum acetate as precursors. The resulting nanofibers were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–Vis spectroscopy, and current–voltage (I–V) properties. The nanofibers had diameters in the range of 60–150 nm. The incorporation of aluminum oxide resulted in a decrease in the crystallite sizes of the zinc oxide nanofibers. Aluminum oxide doped zinc oxide (AOZO) nanofibers exhibited lower bandgap energies compared to undoped zinc oxide nanofibers. However, as the aluminum content (Al/(Al + Zn) × 100%) was increased from 1.70 at.% to 3.20 at.% in the electrospinning solution, the bandgap energy increased resulting in lower conductivity. The electrical conductivity of the AOZO samples was found to depend on the amount of aluminum dopant in the matrix as reflected in the changes in oxidation state elucidated from XPS data. Electrospinning was found to be a productive, simple, and easy method for tuning the bandgap energy and conductivity of zinc oxide semiconducting nanofibers.     

Effect of Cr2O3 on the electrical properties of multicomponent ZnO varistors at the pre-breakdown region

The effect of Cr₂O₃ on the electrical properties of the multicomponent ZnO varistors was investigated using voltage-current curves and impedance spectroscopy. The structure and morphological modifications were analysed by X-ray diffraction and scanning electron microscopy, respectively. It was observed in samples with addition 0.1 mol % Cr₂O₃ that there was an improvement in the electrical properties of the varistors, but the increase in concentration had a deleterious effect on the potential barrier at the grain boundary. The excess Cr₂O₃ segregates at the grain-boundary region and increases the donor concentration, leading to a higher leakage current.     

Effect of P addition on the thermal stability and electrical characteristics of NiSi films

Immersion Ni-P deposition is undoubtedly one of the most important catalytic deposition process, due to its simplicity in operation and low equipment cost. In this study, immersion deposited Ni-P films were used to form Ni-silicide films. Ni-P films with a thickness of 100 nm were fabricated by immersing Si(100) substrates in an aqueous deposition solution. Ni-silicide films were then formed by annealing the samples in a furnace at temperatures ranging from 400 °C to 900 °C for 1 h in an argon ambient. Experimental results indicate that a phosphor addition in Ni films increased the transformation temperature of NiSi to NiSi₂ to 900 °C. Moreover, the feasibility of enhancing the thermal stability of NiSi by varying the interface energy at the NiSi₂/Si interface and the surface energy of a Ni-P-Si capping layer on the NiSi surface is discussed.     

Nonlinear electrical characteristics and dielectric properties of (Ca, Ta)-doped TiO2 ceramics

TiO₂ ceramics doped with 1.0 mol% Ca and different concentrations of Ta were obtained by sintering processing at 1450°C. The microstructures, nonlinear electrical behavior and dielectric properties of the ceramics were investigated. The samples have nonlinear coefficients of = 2.0–5.0 and ultrahigh relative dielectric constants which is up to 10⁵. Especially, the effects of Ta dopant on the nonlinear electrical characteristics and dielectric properties of the (Ca, Ta)-doped TiO₂ ceramics were studied in detail. When the concentration of Ta is 2.0 mol%, the sample exhibits the highest nonlinear coefficient and a comparatively lower dielectric constant. By analogy to a grain-boundary atomic defect model, the effects of Ta and the nonlinear electrical behavior of the TiO₂ system were explained.     

CuO掺杂对 SnO2压敏材料性能的影响

研究了掺杂 CuO对 SnO2· Ni2O3· Ta2O5压敏材料电学性能的影响.实验发现,随着 CuO的 掺杂量从 0.50mol%增加到 1.50mol%,材料的压敏电场强度从 132V/mm升高到 234V/mm,相对 介电常数从 4663减小到 2701.电场强度变化的原因是 CuO掺杂引起的晶粒尺寸变化,随掺杂量 增加晶粒尺寸从 18.8μ m减小到 13.3μ m.未固溶于 SnO2晶格而偏析在晶界上的 CuO阻碍了相 邻 SnO2晶粒的融合 ,这导致了晶粒尺寸的减小.为了解释 SnO2· Ni2O3· Ta2O5· CuO电学非线性 性质的起源,本研究对前人的晶界缺陷势垒模型进行了修正.对该压敏材料进行了等效电路分析, 实验测量与等效电路分析结果相符.     

Effect of spark plasma sintering on microstructure and electrical properties of ZnO-based varistors

Conditions for the elaboration of varistors by spark plasma sintering (SPS) are investigated, using 70 nm zinc oxide nano-particles. For this purpose, the system constituted of zinc oxide, bismuth oxide and other metal oxide is used. Material sintering has been performed by SPS at various temperatures and dwell times. Determination of the microstructure and chemical composition of the as-prepared ceramics are characterized by scanning electron microscopy and X-ray diffraction analysis. Micro-structural analysis revealed the presence of ZnO, spinel and bismuth rich phases. ZnO based Varistor samples sintered within climb speeds 100 and 400 °C/min are compared. The nonlinear electrical characteristics, current–voltage, are measured. The breakdown voltage of the varistors strongly depends on grain sizes. The results show that the best varistors are obtained by SPS at sintering temperatures ranging from 900 to 1200 °C.     

Effect of hafnium addition on the electrical properties of indium zinc oxide thin film transistors

This study reports the performance and stability of hafnium-indium zinc oxide (HfInZnO) thin film transistors (TFTs) with thermally grown SiO2. The HfInZnO channel layer was deposited at room temperature by a co-sputtering system. We examined the effects of hafnium addition on the X-ray photoelectron spectroscopy properties and on the electrical characteristics of the TFTs varying the concentration of the added hafnium. We found that the transistor on-off currents were greatly influenced by the composition of hafnium addition, which suppressed the formation of oxygen vacancies. The field-effect mobility of optimized HfInZnO TFT was 1.34 cm² V⁻¹ s⁻¹, along with an on-off current ratio of 10⁸ and a threshold voltage of 4.54 V. We also investigated the effects of bias stress on HfInZnO TFTs with passivated and non-passivated layers. The threshold voltage change in the passivated device after positive gate bias stress was lower than that in the non-passivated device. This result indicates that HfInZnO TFTs are sensitive to the ambient conditions of the back surface.     

Average Co magnetic moment of R-Co-B (R = Y,Pr and Nd) compounds

We estimate the average Co magnetic moment and account for the moment variation by a model in Y_{n + 1}Co_{3n + 5}B_2n (n = 0, 1, 2, 3 and ∞), Pr_{m + n}Co_{5m + 3n}B_2n (m = 2, n = 1 and m = 2, n = 3), Nd_{m + n}Co_{5m + 3n}B_2n (m = 3, n = 2) and Y₂Co₁₄B compounds. And we obtain the magnetic properties of hypothetical Y_{m + n}Co_{5m + 3n}B_2n (n = 1, m = 2, 3, 4 and 5) compounds.