Impedance spectroscopy study of polycrystalline Bi6Fe2Ti3O18

The electrical properties of polycrystalline Bi₆Fe₂Ti₃O₁₈ are investigated by impedance spectroscopy in the temperature range 30–550°C. The imaginary part of impedance as a function of frequency shows Debye like relaxation. Impedance data are presented in the Nyquist plot which is used to identify an equivalent circuit and the fundamental circuit parameters are determined at different temperatures. The grain and grain-boundary contributions are estimated. The results of bulk a.c. conductivity as a function of temperature and frequency are presented. The activation energies for the a.c. conductivity are calculated. The polaron hopping frequencies are estimated from the a.c. conductivity data.     

Structural and electrical characteristics of Sr(Fe2/3W1/3)O3 ceramics

The polycrystalline samples of Sr(Fe_2/3W_1/3)O₃ (SFW) were prepared by a high-energy ball-milling followed by solid-state reaction technique. The X-ray structural analysis showed the formation of single-phase compound in the tetragonal system, which is a distorted structure of an ideal cubic perovskite. The temperature–frequency dependence of dielectric constant and loss tangent exhibited relaxation behavior of the compound. The studies of impedance parameters (Z′, Z″) as a function of temperature and frequency have confirmed the contribution of bulk resistance of SFW. The small value of activation energy of the compound (～ 0.35 eV) can be explained by mixed ionic–polaronic conductivity mechanism.     

Dielectric and impedance properties of Nd3/2Bi3/2Fe5O12 ceramics

The polycrystalline sample of Nd_3/2Bi_3/2Fe₅O₁₂ was prepared by a high- temperature solid-state reaction technique. Preliminary X-ray structural analysis exhibits the formation of a single-phase tetragonal structure at room temperature. Microstructural analysis by scanning electron microscopy shows that the sintered sample has well defined grains. These grains are distributed uniformly throughout the surface of the sample. Detailed studies of dielectric response at various frequencies and temperatures exhibit a dielectric anomaly at 400 °C. The electrical properties (impedance, modulus and conductivity) of the material were studied using a complex impedance spectroscopy technique. These studies reveal a significant contribution of grain and grain boundary effects in the material. The frequency dependent plots of modulus and the impedance loss show that the conductivity relaxation is of non-Debye type. Studies of electrical conductivity with temperature demonstrate that the compound exhibits Arrhenius-type of electrical conductivity. Study of ac conductivity with frequency suggests that the material obeys Jonscher’s universal power law.     

La替代对Bi2O3-ZnO-Nb2O5陶瓷介电性能的影响

研究了A位La^3＋替代对Bi2O3-ZnO-Nb2O5（BZN）陶瓷结构和介电性能的影响。当La替代量X〈0．5时,陶瓷相结构为单一的立方焦绿石相。随着La替代量的增加,陶瓷样品的晶粒尺寸和密度逐渐减小。低温下的介电弛豫现象随着La替代量的增加也发生有规律的变化,介电常数逐渐减小,弛豫峰峰形逐渐宽化,峰值温度向低温方向移动。与La替代量为0．1、0．15、0．3和0．5相对应的弛豫峰的峰值温度分别为-95℃、-99℃、-109℃和-112℃。     

Sm2O3掺杂Bi2O3-ZnO-Nb2O5基陶瓷的结构与性能

研究了Sm2O3掺杂的bi2O3-ZnO-Nb2O5(BZN)基陶瓷(Bi1.5-xSmxZn0.5)(Zn0.5Nb1.5)O7(O≤x≤0.6,BSZN),的结构及介电性能.结果表明纯BZN陶瓷的结构为立方焦绿石单相;当Sm2O3掺杂量较少(O＜x≤0.5)时,样品的相结构仍然保持立方焦绿石单相;随着Sm2O3掺杂量的进一步增加(x≥0.6),样品出现其它相.同时,试样的介电性能随结构的变化而呈现有规律的变化.     

Synthesis and Magnetic Properties of SrO–Fe2O3–B2O3–Bi2O3 Glass-Ceramics

Glass of nominal composition SrFe₁₂O₁₉ + 12SrB_1.5Bi_0.5O₄ is prepared by rapid quenching from the liquid state and is converted to glass-ceramics containing fine SrFe₁₂O₁₉ particles by heat treatment between 600 and 850°C. The materials are characterized by Mössbauer spectroscopy, x-ray diffraction, differential thermal analysis, electron microscopy, and magnetic measurements. All of the Fe in the glass is shown to be in the oxidation state 3+. The phase transformations accompanying glass crystallization are identified. The coercive field of the samples is shown to increase from 188 to 504 kA/m as the heat-treatment temperature is raised from 600 to 850°C. The composite prepared by heat treatment at 850°C contains submicron-sized SrFe₁₂O₁₉ particles with a thickness-to-diameter ratio of 0.33.     

花瓣状Fe_3O_4/Bi_2O_3复合粒子的制备及光催化活性

用共沉淀法制备的Fe3O4纳米粒子作为种子,通过水热法获得了微米尺寸的Fe3O4/Bi2O3复合粒子。X射线衍射和X光电子能谱表征结果说明复合粒子是由Fe3O4和Bi2O3组成。扫描电子显微镜照片表明复合粒子形貌基本呈规则球形,并且具有花瓣状的三维多级结构。以罗丹明B的催化降解实验为模型考察了不同反应组成、不同反应介质、不同反应温度条件下制备的复合粒子的催化活性。结果表明,当反应条件中m(Bi(NO3)3·5H2O)/m(Fe3O4)为1.9 g∶0.2 g,水作反应介质在160℃时,所制备的复合粒子催化活性最高,对罗丹明B的降解率达95.4%。降解完成后,用磁铁吸附,Fe3O4/Bi2O3很快从体系中分离,可以重新催化降解罗丹明B,实现磁场控制的循环催化。实验发现,Fe3O4/Bi2O3经6次循环利用后,对罗丹明B的降解率仍达88.5%。     

The effect of Bi2O3 on the microstructure and electrical conductivity of ZrO2-Y2O3 ceramics

ZrO₂-Y₂O₃ ceramics with varying Bi₂O₃ contents were prepared and their microstructures and electrical conductivities investigated. The phase stability of cubic fluorite zirconia was disturbed by the introduction of Bi₂O₃ and tetragonal or monoclinic second phases appeared. The effect of the second phases on the intragrain and the grain boundary conductivities was investigated in the 300–550 C range using complex plane analysis in the frequency range of 5 Hz to 13 MHz. It showed that conductivity data could readily be interpreted in terms of possible physical models and electrical equivalent circuits. Tetragonal phases had a small positive influence on the intragrain conductivity. The grain 9boundary resistivity could be diminished by discrete monoclinic second phases which offered more conductive intergranular contacts.     

Dielectric and impedance characteristics of Ba(Bi0.5Nb0.5)O3 ceramics

A lead free polycrystalline material Ba(Bi_0.5Nb_0.5)O₃ was prepared using a high-temperature mixed oxide technique using high purity ingredients. The formation of the material in monoclinic crystal structure was confirmed by an X-ray structural analysis at room temperature. The nature and texture of microstructure by scanning electron microscopy show that the compound has well defined grains uniformly distributed throughout the surface of the sample. Detailed studies of dielectric and impedance properties of the material, carried out in the frequency range of (1 kHz–1 MHz) at different temperatures (30 °C to 475 °C), have shown many interesting properties. Dielectric study showed an existence of diffuse phase transition around 317 °C. The temperature dependence of impedance parameters (impedance, modulus etc.) of the material exhibits a strong correlation of its micro-structure (i.e., bulk, grain boundary, etc.) with the electrical parameters. An existence of negative temperature coefficient of resistance (NTCR) type behavior in the material similar to that of semiconductors was also observed. The complex electric modulus analysis indicates the existence of hopping conduction mechanism in the system with non-exponential type of conductivity relaxation. The nature of variation of dc conductivity with temperature confirms the Arrhenius behavior of the material. The ac conductivity spectra show a typical signature of an ionic conducting system, and are found to obey Jonscher’s universal power law. The temperature dependent pre-exponential factor (A) shows peak and frequency exponent (n) possesses a minimum at transition temperature.     

The effect of Bi2O3 on the electrical and mechanical properties of ZrO2-Y2O3 ceramics

ZrO₂-Y₂O₃ ceramics with varying Bi₂O₃ content have been prepared and their microstructure, electrical conductivity and mechanical properties investigated. The sintering rate is strongly increased at low temperatures (1270 to 1420 K) due to the occurrence of a reactive phase the amount of which decreases during the sintering process. The main fluorite phase has an approximately constant composition at 0.85 ZrO₂-0.13 Y₂O₃-0.02 Bi₂O₃ while the amount of second phase depends on overall composition and sintering procedure. The electrical conductivity is also approximately constant but about a factor of five lower than in ZrO₂-Y₂O₃ ceramics. Typical strength and fracture toughness values are 160 MPa and 1.8 MPa m^1/2, respectively. However, the non-reproducibility of the second phase content and morphology seriously influences both mechanical properties.     

Low-temperature firing and microwave dielectric properties of MgTiO3 ceramics with Bi2O3–V2O5

The effects of Bi₂O₃–V₂O₅ additive on the microstructures, the phase formation and the microwave dielectric properties of MgTiO₃ Ceramics were investigated. The Bi₂O₃–V₂O₅ addition lowered the sintering temperature of MgTiO₃ ceramics effectively from 1400 to 875 °C due to the liquid-phase effect. The microwave dielectric properties were found to strongly correlate with the amount of Bi₂O₃–V₂O₅ addition. The saturated dielectric constant decreased and the maximum Qf values increased with the increasing V₂O₅ content, which is attributed to the variation of the second phase including Bi₂Ti₂O₇, Bi₄V_1.5Ti_0.5O_10.85 and BiVO₄. At 875 °C, MgTiO₃ ceramics with 5.0 mol% Bi₂O₃–7 mol% V₂O₅ gave excellent microwave dielectric properties: ε_r = 20.6,Qf = 10420 GHz (6.3 GHz).     

The crystal structures and dielectric properties of Bi2O3 doped SrBi2Ta2O9 ceramics

Ferroelectric materials with Bi-layered structure such as SrBi₂Ta₂O₉ composition with excess x wt.% Bi₂O₃ (x = 0, 2, and 4) are investigated as the main composition, the effect of excess Bi₂O₃ content and sintering temperatures on the crystal structure and dielectric characteristics of SrBi₂Ta₂O₉ ceramics are developed. Even 1280 °C is used as the sintering temperature of stoichiometry SrBi₂Ta₂O₉ composition, the X-ray diffraction patterns will show that the SrBi₂Ta₂O₉ phase is coexisted with the raw material of Ta₂O₅ and the secondary phases of SrBi₂O₄ and BiTaO₄. For SrBi₂Ta₂O₉ composition with excess 2 wt.%- or 4 wt.%-Bi₂O₃-doped and sintered at 1040 °C, the Ta₂O₅, SrBi₂O₄, and BiTaO₄ phases are eliminated and only the SrBi₂Ta₂O₉ phase is observed in the X-ray diffraction patterns. It is found that sintering temperatures and excess Bi₂O₃ content have large influence on the grain growth, the bulk densities, the maximum dielectric constants, and the Curie temperatures of SrBi₂Ta₂O₉-based ceramics.     

Dielectric and microwave properties study of TiFeNbO6 ceramics added Bi2O3

In this paper the ceramic matrix of TiFeNbO₆ (TFNO) was studied. The TFNO phase was calcined at 1,075 °C and used to prepare the samples, of 2, 4, 6, 8 and 10 wt% of the Bi₂O₃ and sintered at 1,125 °C. These samples were characterized by X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy and dielectric microwave properties. XRD and RS were used to characterize these samples. The samples presented two new phases. The first phase is the tetragonal rutile structure with a space group of P4₂/mnm, equivalent at parent rutile Ti_0.4Fe_0.3 Nb_0.3O₂ (TFNO) with 040725 ICSD code, and the secondary phase belonging to the pyrochlore system Bi_1.721Fe_1.056Nb_1.134O₇ (BFNO), with a space group of Fd-3mZ (227), in a cubic structure. The dielectric properties have shown significant variation for 10 % Bi₂O₃-added sample, because the formation of the new phase (BFNO) contributes with the reduction of τ _f from 281.12 to 77.45 ppm/°C and with increase in ε _r , from 47.23 to 63.77 and an increase in the dielectric loss (tan δ), from 0.0016 to 0.0068, respectively. Even though, Bi₂O₃ additive deteriorates the dielectric loss of the ceramics, the permittivity has enhanced significantly, which is advantageous for reduction of the air gap between the probe and the DRA antennas that influences on the samples for future application in microwave.     

Effects of annealing treatment on the dielectric properties of manganese-modified Pb(Fe2/3W1/3)O3 ceramics

The dielectric properties of thermally treated manganese doped Pb(Fe2/3W1/3)O3 (PFW) ceramics were investigated. Modifications of the dielectric properties by thermal annealing were observed. Air annealing causes a sharpening of the dielectric permittivity and an increase of the permittivity maximum values, more pronounced as the amount of manganese dopant increases. Oxygen annealing does not cause evident variations in the dielectric permittivity curve. The presence of oxygen vacancies is evinced by thermal gravimetric measurements. The role of oxygen vacancies, as well as the associations of manganese ions with oxygen vacancies, on the annealing process, is proposed and discussed. © 1998 Chapman & Hall     

Preparation and characterization of two new dielectric ceramics Ba4NdTiNb3O15 and Ba3Nd2Ti2Nb2O15

Two new cation-deficient hexagonal perovskites Ba₄NdTiNb₃O₁₅ and Ba₃Nd₂Ti₂Nb₂O₁₅ were prepared in the BaO–Nd₂O₃–TiO₂–Nb₂O₅ system by high temperature solid-state reaction route. The phase and structure of the ceramics were characterized by X-ray diffraction and scanning electron microscope (SEM). The microwave dielectric properties of the ceramics were studied using a network analyzer. Ba₄NdTiNb₃O₁₅ has a dielectric constant of 38.15, a high-quality factors (Q _u ×f >18 700 at 5.4422 GHz), and a small temperature coefficient of resonant frequency ( _f )+12 ppm °C^–1 at room temperature; Ba₃Nd₂Ti₂Nb₂O₁₅ has a higher dielectric constant of 46.83 with high-quality factors Q _u ×f >19 500 at 5.0980 GHz, and _f +28 ppm °C^–1.     

氧化铋对微晶玻璃的相转变和性能的影响

为研究Bi2O3在堇青石基微晶玻璃烧结中的作用及其添加量对微晶玻璃的相转变和性能的影响,采用烧结法制备了不同Bi2O3含量的微晶玻璃,并对其进行了X射线衍射分析、显微分析和性能测试.结果表明:Bi2O3的加入降低了堇青石的u相向a相转变的温度,并有效促进微晶玻璃的烧结致密化;烧结样品的介电常数和抗折强度均随着Bi2O3加入量的增加而增加,且与密度变化规律相似;当Bi2O3添加量(质量分数)达5%时样品的介质损耗因子最低(＜10-3);微晶玻璃烧结样品的热膨胀系数基本符合线性规律.     

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.