Study of structure and dielectrc properties of non-stoichiometric Bi2O3-ZnO-Nb2O5 ceramics

Bi-based ceramics with pyrochlore structure exhibit interesting dielectric properties such as high dielectric constant and small dielectric loss at high frequency and low firing temperature. Structure and dielectric properties of non-stoichiometric ceramics Bi_1.5?x ZnNb_1.5O_7?1.5x (with x?=??0.25～0.6) were investigated. The compounds departured from stoichiomeric compositions lead to structural parameters change. The second phase appeared when x?≥?0.4. The lattice parameters of cubic pyrochlore Bi_1.5?x ZnNb_1.5O₇ and grain size decreased as x increased. The experimental results show that dielectric constant decrease with increasing of the x value. The dielectric relaxation and defect resulting from non-stoichiometric ceramics Bi_1.5?x ZnNb_1.5O_7?1.5x were discussed.     

Electrical conductivity and thermoelectric power of a-Ge20 Se80 − x Bi x thin films

The dc electrical conductivity and thermoelectric power of a-Ge₂₀Se_{80 − x} Bi _x (x = 0, 4, 6, 8, 10, 12) thin films are reported in the present work. The thin films were deposited by flash evaporation at 10^{− 5} Torr pressure and were well-characterized taking XRD, XRF, DSC and EPMA measurements of the system. The dc conductivity was measured over a temperature range 77 to 476 K. Conduction type and activation energies of electrical conductivity have been determined. The electrical transport takes place via two modes extended state conduction at higher temperatures and variable range hopping at lower temperatures. The conductivity was found to change by few orders of magnitude with Bi doping and the electrical activation energies (Δ E _σ) were found to decrease with increasing Bi content. The density of localized states and pre-exponential factor were determined. The thermopower measurements carried out using differential dc method in the temperature range 4.2 to 300 K and the activation energy (Δ E _s ) for TEP determined. The change in band gap with increasing Bi content is due to increased band tailing and increase of Bi–Se bonds and decrease of Se–Se bonds thus leading to the modification of the network structure of Ge₂₀Se₈₀ system.     

Electro-caloric behaviors of lead-free Bi0.5Na0.5TiO3-BaTiO3 ceramics

Electro-caloric (EC) properties of lead-free Ba_0.5Na_0.5TiO₃-xBaTiO₃ (BNT-xBT) ceramics prepared by citrate method are investigated at temperatures of 30–250°C. Based on thermodynamics calculations, BNT-xBT (x = 0, 0.05, 0.06, 0.1, 0.25, 0.3) are found to show EC effects different with other lead-based or lead-free ferroelectric ceramics, i.e., they absorb heats (refrigeration effect) during the processes of field application while other ferroelectric ceramics show refrigeration effect during the processes of field removal. The EC temperature change of BNT-xBT can be as large as 2.1°C under an electric field of 60 kV/cm, which is larger than most of the lead-free ferroelectric bulk ceramics. When x is close to the morphotropic phase boundary (x ~ 0.06–0.1), the EC temperature change of BNT-xBT shows a maximum near the ferroelectric to anti-ferroelectric transition temperature, which is characterized by dynamic mechanical analysis. This study suggests that these lead-free ferroelectric materials are promising in the practical application as EC coolers.     

碲化铋温差发电组件的寿命试验及其分析

通过寿命试验研究了TEG1-127-1.4-1.6-250型碲化铋材料温差发电组件在模拟使用过程中电输出性能的衰减规律,并讨论了碲化铋材料制备工艺对温差发电组件可靠性的影响.研究表明,在热面温度250℃,2250 h的寿命试验中,碲化铋材料温差发电组件的电输出性能衰减速率随时间的增加不断减小.热压制备碲化铋材料发电组件...     

High-temperature stable dielectrics in Mn-modified (1-x) Bi0.5Na0.5TiO3-xCaTiO3 ceramics

In the current work, the bulk (1-x) Bi_0.5Na_0.5TiO₃-xCaTiO₃ [BNCT100x] system was synthesized via solid-state route. CaTiO₃ in solid solution with Bi_0.5Na_0.5TiO₃ was observed to decrease the dielectric constant at higher temperature and raise the dielectric constant at lower temperature. Polarization hysteresis measurements indicated that the ferroelectricity of Bi_0.5Na_0.5TiO₃ was weakened with an increase of CaTiO₃, resulted in the shift of the depolarization temperature (T _d) toward lower temperatures. X-ray diffraction analysis revealed that TiO₂ was produced as a secondary phase due to the losses of Bi and Na during milling and sintering processes. Moreover, the addition of Ca promoted the segregation of Ti out of BNT grains. Dielectric properties of BNCT12 ceramics with different dopant levels of Mn were characterized as a function of temperature for potential use of high-temperature capacitors. Modification of BNCT12 materials with Mn improved the temperature characteristic of capacitance (?55°C to 250°C, △C/C_25°C ≤ ±15%). Finally, by doping 1.5 wt% Mn, the dielectric constant at room temperature could reach over 900, with a low dielectric loss below 1% and a high insulation resistivity about 10¹² Ω?cm. Furthermore, a small amount of Mn influenced the microstructure in the way to inhibit the long grains and grain growth of BNCT solution ceramics. However, excess Mn caused abnormal grain growth, and therefore, rectangle grains appeared again.     

热压法制备P型Bi2Te3基温差电材料研究

以P型赝二元Bi2Te3-Sb2Te3体系温差电材料区熔晶棒为前驱体,采用真空热压烧结法制备材料样品。测试热压前后材料样品性能,测试结果表明:热压样品较区熔材料具有更高的致密度和机械强度,改善了Bi2Te3基温差电材料易沿解理面发生劈裂的现象;同时,热压工艺促使了材料内部晶体结构和载流子浓度的变化,引起材料电导率的降低和塞贝克系数的改变,导致材料热导率显著降低。综合考虑材料各项性能参数,热压材料的热电优值基本与区熔材料相当,但前者的力学强度明显优于后者,在实际使用中将占有明显的优势。     

Investigation of the physical properties of Bi1.5-xCdxZn0.92Nb1.5O6.92-x/2 pyrochlore ceramics

For the purpose of dielectric parameters tuning Bi_1.5Zn_0.92Nb_1.5O_6.92 (BZN) pyrochlore ceramics were subject to cadmium doping in accordance to the chemical formula; Bi_1.5-xCd_xZn_0.92Nb_1.5O_6.92-x/2 for 0.10 ≤ x ≤ 0.50. The main physical properties of the doped samples were investigated by means of X-ray diffraction, scanning electron microscopy associated with energy dispersion spectroscopy, temperature dependent dielectric constant and temperature dependent electrical resistivity to obtain the crystalline structure, the lattice parameter, the relative density, the surface morphology and chemical composition. Optimization of single phase Cd doped samples were possible for x?≤?0.14, beyond this limit, ZnO and Zn₃Nb₂O₈ minor phases grow through the structure of the BZN. For samples which exhibit single BZN phase, the dielectric constant, the electrical resistivity and the resistivity activation energy increased with increasing Cd content. The maximum obtainable dielectric constant as 259 and 224 with high signal quality factor of 690 and 1090 at 25 and 200 °C, respectively, was for the sample doped with 0.14 Cd. These values are promising for implantation of BZN in RF and microwave technology as a resonator with high quality signal.     

Processing and property of textured lead-free SrTi4Bi4O15 piezoelectric ceramics

In this paper, textured SrTi₄Bi₄O₁₅(SBT) ceramics were produced by tape casting and hot-pressing to improve the piezoelectric property. Plate-like SBT powders were synthesized by a molten salt synthesis (MSS) method. Tape casting and hot-pressing were employed to obtain (00l) oriented SBT ceramics at 1,000°C with a density of 98.3%. Anisotropy characters of textured SBT were measured by piezoelectric coefficient and hysteresis loop. Compared with randomly oriented ceramics, textured SBT shown enhancements in the piezoelectric properties. Property of perpendicular to hot pressing direction (d ₃₃?=?17 pC/N) was more eminent than that of parallel to hot pressing direction (d ₃₃?=?1 pC/N).     

Bi2Te3基温差发电组件的热应力和结构参数选择

温差电材料性能决定了温差发电组件(TEM)的发电功率及转换效率,而在使用过程中由于环境因素的影响,对其机械性能也提出了一定的要求.热压法制备的Bi2Te3基温差电材料密度和强度均有提高,缓解了区熔法制备的Bi2Te3基温差电材料在平行于晶体方向上易发生解理破坏的问题,但还不能完全避免.通过分析Bi2Te3基温差电材料沿...     

Dielectric and nonlinear electrical behaviors of Ce-doped CaCu3Ti4O12 ceramics

We present a remarkable effect of Ce doping on the dielectric and nonlinear electric properties of CaCu₃Ti₄O₁₂ ceramics. Microstructure analysis indicates that Ce-doped CCTO ceramics are composed of large and small grains. Our results indicate that only 2.5 at. % Ce doping can suppress the dielectric permittivity in CaCu₃Ti₄O₁₂ by up to two orders of magnitude (from 10⁴ to 10² ), and the nonlinear varistor characteristics disappear completely, which may be due mainly to the Cu⁺ ions?? disappearing caused by the Ce doping.     

Dielectric and piezoelectric properties of (K0.5Na0.5)(Nb0.97Sb0.03)O3 ceramics doped with Bi2O3

In this study, to develop the optimal composition of ceramics for low loss piezoelectric actuator and ultrasonic motor applications, (K_0.5Na_0.5)(Nb_0.97Sb_0.03)O₃?+?0.009 K_5.4Cu_1.3Ta₁₀O₂₉?+?0.1wt%Li₂CO₃?+?xwt%Bi₂O₃(x?=?0?~?0.9) lead-free piezoelectric ceramics with a fixed quantity of 0.009 K_5.4Cu_1.3Ta₁₀O₂₉ (abbreviated as KCT) were manufactured using the conventional solid-state solution processes. The effects of Bi₂O₃ addition on the dielectric and piezoelectric properties were then investigated. From the X-ray diffraction analysis result the specimens demonstrated orthorhombic symmetry when Bi₂O₃ was less 0.6?wt%, a pseudo-cubic phase appeared when Bi₂O₃ was 0.9?wt%. SEM images indicate that a small amount of Bi₂O₃ addition affect the microstructure. The piezoelectric properties of (K_0.5Na_0.5)(Nb_0.97Sb_0.03)O₃ ceramics were greatly improved by a certain amount of Bi₂O₃ addition. Excellent properties of density?=?4.54?g/cm³, relative densities?=?98.5?%, k _p?=?0.468, Q _m?=?1,715 and d ₃₃?=?183 pC/N were obtained with a composition of 0.3?wt% Bi₂O₃     

Phase transition behaviors of (Na1/2Bi1/2)1−x TiPb x O3 thin films

Ferroelectric thin films of (Na_1/2Bi_1/2)_1?x TiPb _x O₃ have been synthesized via a sol–gel route. Structural changes of the films were investigated by using X-ray diffraction (XRD) and Raman spectroscopy over the composition range 0?<?x?<?0.9. There occur different nano-sized clusters in the films. More interestingly, in contrast to the previously reported results on (Na_1/2Bi_1/2)_1?x TiPb _x O₃ bulk ceramics, the ferroelectric thin films exhibit a rhombohedral–tetragonal structure change at x?=?0.4–0.5, together with a long range tetragonal symmetry at x?≥?0.8. The unique phase transition behaviors are discussed in relation to the growth of Pb²⁺TiO₃ clusters upon the substitution of Pb²⁺ for Na⁺/Bi³⁺ cations in the (Na_1/2Bi_1/2)_1?x TiPb _x O₃ films.     

Influence of vanadium substitution on the conductivity of Bi3.25La0.75Ti3O12 and Bi3.25La0.75Ti2.97V0.03O12 ceramics

We have fabricated Bi_3.25La_0.75Ti₃O₁₂ and Bi_3.25La_0.75Ti_2.97V_0.03O₁₂ ceramics using the conventional solid-state reaction method. We measured their dc conductivity and analyzed the impedance spectroscopy in order to clarify the influence of vanadium substitution for titanium site on Bi_3.25La_0.75Ti₃O₁₂ ceramic. The vanadium substitution for titanium site in Bi_3.25La_0.75Ti₃O₁₂ can reduce the Bi cation and oxygen vacancies. Furthermore, the elimination of these defects, trapped in the grain boundary and grain-electrode interface, significantly reduces the influence of domain pinning, which would be responsible for the improvement in the ferroelectricity and piezoelectricity.     

LiMn2O4在聚合物锂离子蓄电池中的高温性能

在电解液中的溶解是尖晶石LiMn2O4高温不可逆容量损失的主要原因。聚合物锂离子蓄电池结构特点及聚合物材料与电解液相互作用可以影响高温下尖晶石LiMn2O4在电解液中的溶解及扩散行为,降低尖晶石LiMn2O4的不可逆容量损失。使用尖晶石LiMn2O4为正极活性材料,利用厦门大学宝龙电池研究所聚合物锂离子蓄电池中试生产线,在特定的工艺条件下制备容量为600mAh的实验电池。实验表明,在聚合物锂离子蓄电池中LiMn2O4材料高温稳定性明显改善,实验电池在常温下循环200次,容量保持率在80%以上;55℃下循环30次,容量保持率超过92%;70℃下循环10次,容量保持率达到96%。     

Control of 0.2CaTiO3-0.8Li0.5Nd0.5TiO3 microwave dielectric ceramics by additions of Bi2Ti2O7

Ceramics of 0.2CaTiO₃-0.8Li_0.5Nd_0.5TiO₃) have been prepared by the mixed oxide route using additions of Bi₂O₃-2TiO₂ (up to 15 wt%). Powders were calcined 1100^∘C; cylindrical specimens were fired at temperatures in the range 1250–1325^∘C. Sintered products were typically 95% dense. The microstructures were dominated by angular grains 1–2 μm in size. With increasing levels of Bi₂O₃-2TiO₂ additions, needle and lath shaped second phases developed. For Bi₂Ti₂O₇ additions up to 5 wt%, the relative permittivity increased from 95 to 131, the product of dielectric Q value and measurement frequency increased from 2150 to 2450 GHz and the temperature coefficient of resonant frequency (τ _f ) increased from −28pp/^∘C to +22pp/^∘C. A product with temperature stable τ _f could be obtained at ∼2 wt% Bi₂Ti₂O₇ additions. For high levels of additives, there is minimal change in relative permittivity, the Qxf values degrade and τ _f becomes increasingly negative.     

铋改性二氧化锰在电化学电容器中的应用

采用液相沉淀法合成二氧化锰并在其表面包覆氧化铋,以期改善二氧化锰的电容性能。X射线衍射(XRD)测试表明合成的二氧化锰为无定形结构,包覆Bi2O3后材料转变为结晶度较差的α-Mn O2;扫描电镜(SEM)和X射线能谱(EDX)测试结果显示其为无规则颗粒状且表面覆盖着疏松的Bi2O3。循环伏安、恒电流充放电和电化学阻抗谱测试表明包覆5%(质量分数)Bi2O3的二氧化锰具有最好的电容性能。在电流密度分别为200、400和600 m A/g时,电极比电容分别为352.8、307.2和277.2 F/g,相比未包覆Mn O2分别提高了17.1%、15.0%和9.5%。     

尖晶石型ZnMn2O4的合成及其电化学行为

主要报道尖晶石型ZnMn2 O4的合成及其在非水介质中的电化学行为。实验表明 ,以醋酸锰、醋酸锌、碳酸锰和碳酸锌为原料 ,在 90 0℃左右合成的ZnMn2 O4具有尖晶石结构 ,初始容量达到 14 0mAh/ g ,且具有良好的可逆性 ,在Zn| 1mol/LZn(ClO4) 2 +PC|ZnMn2 O4模拟电池体系中 ,循环 2 0 0多次后容量衰减到 12 5mAh/ g。     

High dielectric permittivity of SrBi2Nb2O9(SBN) added Bi2O3 and La2O3

In this paper, the structural and dielectric properties of SrBi₂Nb₂O₉ (SBN) as a function of Bi₂O₃ or La₂O₃ addition level in the radio (RF) and microwave frequencies were investigated. The SBN, were prepared by using a new procedure in the solid-state reaction method with the addition of 3; 5; 10 and 15 wt.% of Bi₂O₃ or La₂O_3. A single orthorhombic phase was formed after calcination at 900 °C for 2 h. The analysis by x-ray diffraction (XRD) using the Rietveld refinement confirmed the formation of single-phase compound with a crystal structure (a?=?5.5129 Å, b?=?5.5183 Å and c?=?25.0819 Å; α?=?β?=?γ?=?90°). Scanning Electron Microscope (SEM) micrograph of the material shows globular morphologies (nearly spherical) of grains throughout the surface of the samples. The Curie temperature found for the undoped sample was about 400 °C, with additions of Bi³⁺, the temperature decreases and with additions of La³⁺ the Curie temperature increased significantly above 450 °C. In the measurements of the dielectric properties of SBN at room temperature, one observe that at 10 MHz the highest values of permittivity was observed for SBN5LaP (5%La₂O₃) with values of 116,71 and the lower loss (0.0057) was obtained for SBN15LaP (15%La₂O₃). In the microwave frequency region, Bi₂O₃ added samples have shown higher dielectric permittivity than La₂O₃ added samples, we highlight the SBN15BiG (15 % Bi₂O₃) with the highest dielectric permittivity of 70.32 (3.4 GHz). The dielectric permittivity values are in the range of 28–71 and dielectric losses are of the order of 10^?2. The samples were investigated for possible applications in RF and microwave components.     

Piezoelectric properties of (Na0.465K0.465Bi0.07)(Nb0.93Ti0.07)O3 ceramics with MnO2 addition

In this study, (Na_0.465K_0.465Bi_0.07)(Nb_0.93Ti_0.07)O₃ ceramics with MnO₂ addition were prepared by conventional mixed oxide method. The effects of MnO₂ addition on the structural and electrical properties of the specimens were investigated for the application of piezoelectric devices. As the results of X-ray diffraction analysis, all specimens showed the typical polycrystalline perovskite structure without presence of the second phase. Sintered densities increased with increasing the addition amount of MnO₂ and the specimen added with 0.06 mol% of MnO₂ showed the maximum value of 4.87 g/cm³. Average grain size increased and densification increased with an increasing of MnO₂ contents. The electromechanical coupling factor, dielectric constant, dielectric loss, d₃₃ and Curie temperature of the 0.06 mol% of MnO₂ doped (Na_0.465K_0.465Bi_0.07)(Nb_0.93Ti_0.07)O₃ specimens were 0.32, 1309, 0.016, 122 and 465 °C, respectively.