Microstructure, electrical properties, and dc aging characteristics of Tb4O7-doped ZnO-based varistors

The microstructure, electrical properties, and dc-accelerated aging characteristics of Tb₄O₇-doped ZnO-based varistors were investigated for different Tb₄O₇ amounts and sintering temperatures. The sintered density increased with increasing Tb₄O₇ amount and sintering temperature. The average grain size decreased with increasing Tb₄O₇ amount and increased with increasing sintering temperature. The varistor voltage and nonlinear coefficient increased with increasing Tb₄O₇ amount and decreased with increasing sintering temperature. The stability was worse with increasing Tb₄O₇ amount for the varistors sintered at 1,300 °C. The 0.5 mol% Tb₄O₇-doped varistors sintered at 1,350 °C exhibited a good stability for dc-accelerated aging stress of 0.95 V _{1 mA}/150 °C/24 h.     

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.     

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.     

Structural and electrical studies on Bi2VO5.5/Bi4Ti3O12 multilayer thin films

The textured multilayer (ML) thin films of bismuth layered ferroelectric (FE) compounds, Bi₂VO_5.5 (BVO) and Bi₄Ti₃O₁₂ (BTO) with different individual layer thicknesses were fabricated via pulsed laser deposition technique on Pt(111)/TiO₂/SiO₂/Si substrates. X-ray diffraction studies confirmed that BVO and BTO retained their respective crystal structures in these multilayer (ML) thin films. The atomic force microscopy and scanning electron microscopy studies showed smooth and dense microstructures. The polarization hysteresis (P?CE) studies on a representative (BVBT30) ML thin film at 300 K confirmed the remnant polarization (2P _r ) and coercive field (E _c ) to be ~20 ??C/cm² and 250 kV/cm, respectively. The value of P _r obtained was greater than that of the single layer thin film of BVO (P _r  ~ 5.6 ??C/cm²). The room temperature dielectric constant (??_r??) and the loss (D) for BVBT30 ML measured at 100 kHz were 170 and 0.01, respectively. The frequency and temperature dependent dielectric constant, impedance, modulus and ac conductivity of these ML thin films were studied as a function of frequency (100 Hz?C1 MHz) in the 25?C300 °C temperature range. Two distinct electrical responses were observed in these films, which were attributed to the grain effects at low temperatures and grain boundary effects at higher temperatures. The frequency dependent electrical conductivity was fitted well with the double power law which evidenced two different types of contributions to the conductivity; the low frequency conductivity being due to the short range translational hopping and the high frequency conductivity was due to the localized or reorientational hopping.     

A位掺杂Bi4Ti3O12陶瓷的铁电性能研究

用传统固相烧结工艺,制备了纯相的Bi4Ti3O12 (BTO)陶瓷,A位掺杂的Bi3.25La0.75Ti3O12(BLT),Bi3.15Nd0.85Ti3O12(BNdT)铁电陶瓷.X射线衍射结果表明,所有样品均为单一的层状钙钛矿结构,La、Nd掺杂未改变BTO的晶体结构.铁电测试结果表明,BTO、BLT和BNdT陶瓷的剩余极化2Pr值分别为12.4、23.8和39.4μC/cm2.A位掺杂后,BLT、BNdT的2Pr值比未掺杂的BTO分别提高了1.92和3.18倍.漏电流测试表明,BLT、BNdT陶瓷的漏电流密度比BTO明显降低.A位掺杂显著提高了BTO陶瓷的铁电性能.     

Sintering and characterization of Bi4Ti3O12 ceramics

Polycrystalline ferroelectric Bi₄Ti₃O₁₂ ceramics have been prepared by the method of reactive liquid phase sintering. The sintering behaviour of the Bi₂O₃-TiO₂ composite was examined by plotting the isothermal densification curves. The results indicate that the starting oxides are involved in the reaction even at temperatures lower than or equal to 800°C, but the reaction advances at a very slow rate. Above solidus, the liquid phase promotes an extended reaction. Saturation observed in two densification curves, at 875 and 1100°C demonstrate that the reaction proceeds by two steps. A completion of the Bi₄Ti₃O₁₂ formation occurs after 60 min of sintering at 1100°C. Optical micrographs of sintered bismuth titanate ceramics show randomly oriented ferroelectric grains separated by a paraelectric intergranular layer. The Bi₄Ti₃O₁₂ crystallites exhibit a platelike morphology, similar in the appearance to mica, as evidenced by scanning electron micrographs. Isothermal annealing (750 to 950°C) does not affect the microstructure and electric properties of sintered bismuth titanate. The considerable value of dielectric permittivity and the appearance of hysteresis have been correlated to the presence of oxygen vacancies within the pseudotetragonal structure of Bi₄Ti₃O₁₂. The oxygen vacancies are preferentially sited in the vicinity of bismuth ions as evidenced by X-ray photoemission data. XPS and AES measurements confirm that the surface concentration of cations comprising the Bi₄Ti₃O₁₂ ceramics does not deviate from the nominal bulk composition.     

Ag@AgCl改性Bi4Ti3O12的制备及其可见光催化性能

以五水硝酸铋为铋源、钛酸四丁酯为钛源,通过水热法制备了Bi4Ti3O12,再以硝酸银为银源、盐酸为氯源,采用光照还原Bi4Ti3O12得到Ag@AgCl/Bi4Ti3O12复合材料.利用XRD、UV-Vis DRS、SEM、TEM、BET和XPS等方法对所制备材料的组成和结构进行表征和分析,并以甲基橙(MO)溶液的脱色...     

Microstructure and electrical properties of LaMnO3-CaCu3Ti4O12 composite ceramics

In this study, xLaMnO₃-(1???x)CaCu₃Ti₄O₁₂ (0?≤?x?≤?0.7) composite ceramics have been prepared by the conventional solid-state method. XRD results show that the composite ceramics are mainly composed of LaMnO₃ and CaCu₃Ti₄O₁₂ phases. Electrical property analysis shows that the resistivity ρ₂₅ gradually decreases from 2.17?×?10⁸ to 1.74?×?10⁵ Ω·cm with increasing LaMnO₃ content. The relationship between lnρ and 1000/T is not linear and changes around 350 °C. In the temperature range of 0–350 °C, the activation energy Ea_0–350 °C decreases gradually with the increase of the LaMnO₃ content. In the temperature range of 350–500 °C, the activation energy Ea_{350–500 °C} increases first and then decreases, which is related to the variation of oxygen vacancy. The compounding of LaMnO₃ gives rise to the decrease in B value, thus, providing the potential for the applications of wide temperature range thermistors. After annealing, the coefficient of aging (ΔR/R) of the composites decreases from 23.73 to 3.01%.

     

Sandwiched BaNd2Ti4O12/Bi4Ti3O12/BaNd2Ti4O12 ceramics prepared by spark plasma sintering

Spark plasma sintering (SPS) combined with heat treatment was investigated to prepare laminated ceramics from compositions having quite different sintering temperatures. Although the optimal sintering temperature of BaNd₂Ti₄O₁₂ (BNT) ceramics was much higher than that of Bi₄Ti₃O₁₂ (BIT) ceramics, sandwiched BaNd₂Ti₄O₁₂/Bi₄Ti₃O₁₂/BaNd₂Ti₄O₁₂ (BNT/BIT/BNT) composite ceramics were successfully prepared with this new method. The results of scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) showed that the BNT layers and the BIT layer were well bonded and no significant diffusion between them was observed. The temperature coefficient of dielectric constant of the laminated ceramic was found to be much smaller than that of BNT ceramic.     

Effect of Sm2O3 dopant on microstructure and electrical properties of ZnO-based varistor ceramics

ZnO-based varistor ceramics doped with fixed Y₂O₃ and different Sm₂O₃ have been prepared by the conventional solid-state reaction route, and the phase composition, microstructure and electrical properties have been investigated by XRD, SEM and a V–I source/measure unit. The XRD analyses show the presence of primary phase ZnO and some minor secondary phases. Doping appropriate contents of Sm₂O₃ decrease the leakage current and enhance nonlinearity characteristics of ZnO-based varistor ceramics markedly. The varistor ceramics with 0.25 mol% Sm₂O₃ sintered at 1,125 °C for 1 h exhibit reasonable electrical properties with the breakdown field of 446.4 V/mm, the nonlinear coefficient of 65.8 and the leakage current of 2.36 μA/cm². The results illustrate that doping Y₂O₃ and Sm₂O₃ may be a promising route for the production of ZnO-based varistor ceramics with good electrical properties.     

Effect of Tantalum ion doping on the structure and electrical properties of Bi3Ti1.5W0.5O9-Bi4Ti3O12 intergrowth bismuth-layered ceramics

Journal of Materials Science: Materials in Electronics - Bi7Ti4.5-xTaxW0.5O21 (BTW-BIT-xTa, x?=?0.00, 0.05, 0.10, 0.15, 0.20, 0.30) intergrowth bismuth-layered ceramics were fabricated...     

Microstructure and electrical properties of ZnO-based varistors prepared by high-energy ball milling

ZnO-based varistor ceramics were prepared at sintering temperatures ranging from 900 °C to 1,300 °C, by subjecting the mixed oxide powders to high-energy ball milling (HEBM) for 0, 5, 10 and 20 h, respectively. Varistor ceramics prepared by HEBM featured denser body, better electrical properties sintered at low-temperature than at traditional high-temperature. The high density is due to the refinement of the crystalline grains, the enhanced stored energy in the powders coming from lattice distortion and defects as well as the promotion of liquid-phase sintering. Good electrical properties is attributed to proper microstructure formed at low-temperature and improved grain boundary characteristics resulting from HEBM. With increasing sintering temperatures, the electrical properties and density became worse due to the decrease in amount of Bi-rich phase. Temperature increased up to 1,200 °C or above, the Bi-rich phase vanished and the ceramics exhibited very low nonlinear coefficient.     

Synthesis and characteristics of nature-superlattice-structured Bi3TiNbO9–Bi4Ti3O12 ferroelectric thin films by MOD

Natural-superlattice-structured ferroelectric thin films, Bi₃TiNbO₉–Bi₄Ti₃O₁₂ (BTN–BIT), have been synthesized on Pt/Ti/SiO₂/Si by metal organic decomposition (MOD) using BTN–BIT (1 mol:1 mol) solution. BTN–BIT films show natural-superlattice peaks below 2θ = 20° in X-ray diffraction patterns, which indicate that the BTN–BIT films annealed at 700–800 °C in O₂ ambient are consisted of iteration of two unit cells of Bi₃TiNbO₉ and one unit cell of Bi₄Ti₃O₁₂. As the annealing temperature increases from 600 to 750 °C, uniform and crack-free films, better crystallinity and ferroelectric properties can be obtained, but the pyrochlore phase in BTN–BIT films annealed over 800 °C would impair the ferroelectric properties. With the increase of O₂ flow rate from 0.5 to 1.5 L/min, both remanent polarization P_r and coercive electric field E_C increase, which are mainly attributed to reduction of the vacanvies of Bi and oxide ions in the films. Natural-superlattice-structured BTN–BIT thin films having 2–1 superlattice annealed at 750 °C in O₂ ambient with a flow rate of 1.5 L/min exhibit superior ferroelectric properties of P_r = 23.5 μC/cm² and E_C = 135 kV/cm.     

Bi4Ti3O12掺杂对(Bi1.5Zn0.5)(Zn0.5Nb1.5)O7陶瓷结构与介电性能的影响

研究了Bi4Ti3O12掺杂对(Bi1.5Zn0.5)(Zn0.5Nb1.5)O7(BZN)陶瓷烧结特性、相结构和介电性能的影响.采用传统的固相反应法制备样品,X射线衍射技术分析相结构,SEM观察表面形貌.结果表明,Bi4Ti3O12掺杂能有效地促进烧结,提高介电常数ε,降低介电损耗tgδ,优化介电频率温度系数αε.1000℃烧结8%(摩尔分数) Bi4Ti3O12掺杂的BZN陶瓷具有较好的介电性能ε=192,tgδ= 4.21×10-4,αε=-3.37×10-4/℃.     

硅衬底Bi_4Ti_3O_(12)和Bi_(3.25)La_(0.75)Ti_3O_(12)铁电薄膜的慢正电子束研究

对硅衬底生长的Bi4Ti3O12和Bi3.25La0.75Ti3O12薄膜样品测量了慢正电子多普勒展宽谱,得到了S参数随正电子注入能量的变化。通过对S参数和W参数的分析,讨论了这类材料中的捕获态特征和结构特点,结果表明,薄膜与硅衬底界面的缺陷为空位-氧复合体,La的掺杂有助于阻止空位-氧复合体向界面的扩散。     

Giant dielectric and low voltage varistor behaviors of Ba-doped Bi1/2Na1/2Cu3Ti4O12 ceramics

Bi_1/2?xNa_1/2?xBa_2xCu₃Ti₄O₁₂ (x = 0, 0.025, 0.05, 0.075) polycrystalline ceramics are prepared by a modified Pechini method. Effect of Ba doping on the dielectric and nonlinear electrical behaviors are investigated in detail. All the samples exhibit giant dielectric effect and nonlinear electrical behavior. Compared with Bi_1/2Na_1/2Cu₃T_i4O₁₂ ceramics, the permittivity drops down and the nonlinear electrical behavior shifts to low voltage area by Ba doping. The permittivity reduces from 20,004 to 7,006 at 1 kHz. The breakdown voltage and nonlinear coefficient values decrease to 10.8 V/mm and 1.5, respectively. Additionally, the electrostatic barrier height drops down to 0.66 eV. Giant dielectric response and nonlinear electrical behavior can be interpreted in terms of internal barrier layer capacitors model. These results imply that Ba substitution can adjust the dielectric and nonlinear electrical behaviors of Bi_1/2Na_1/2Cu₃T_i4O₁₂ ceramics, which is a promising candidate for low voltage varistor materials.