Structural and dielectric properties of Pb(Li1/4Sm1/4Mo1/2)O3 ceramics

The ceramic samples of lithium-samarium modified lead molybdate, Pb(Li_1/4 Sm_1/4 Mo_1/2)O₃ (PLSM)—a member of ABO₃ family were prepared by solid state reaction technique at ≈ 600–700°C. Preliminary X-ray analysis suggests the formation of single phase orthorhombic compound of PLSM. Studies of surface morphology, uniform particle/grain distribution, and presence of elements in the compound were completed using scanning electron microscope (SEM). Measurements of dielectric constant (ɛ), loss (tanδ) and conductivity (σ) at different frequencies and temperatures provided that the compound has a strong dielectric anomaly at 107°C.     

Some electrical and magnetic properties of γ-Fe2O3

γ-Fe₂O₃ synthesized from FeC₄H₄O₄·4H₂O has been studied using various techniques. The phase transformation observed by electrical conductivity measurements agrees well with the initial magnetization measurement. The magnetic hysteresis values compare with those ofγ-Fe₂O₃ samples synthesized using established procedures.γ-Fe₂O₃ particles obtained were circular in shape showing a well resolved six narrow bands in Mössbauer spectrum. The presence of hydrogen ferrite phase was also confirmed by electrical and magnetic measurements.     

Influence of Ag2SO4 addition on the electrical conductivity of the Li2O:B2O3 system

Glasses in the Li₂O:B₂O₃:Ag₂SO₄ system were prepared with varying silver sulphate contents. From the present results it can be said that the amorphous matrix accepts Ag₂SO₄ up to 5 mol% without any devitrification. The enhancement in conductivity with change in the structure of metaborate glass is due to Ag₂SO₄.     

Effect of temperature on nonlinear electrical behavior and dielectric properties of (Ca, Ta)-doped TiO2 ceramics

TiO₂ ceramics doped with 0.75 mol% Ca and 2.5 mol% Ta were sintered at different temperatures ranging from 1300 to 1450°C. The effects of sintering temperature on the microstructure, nonlinear electrical behavior, and dielectric properties of the ceramics were studied. The sample sintered at 1300°C exhibits the highest nonlinear coefficient (5.5) and a comparatively lower relative dielectric constant.     

Low-temperature fabrication of BaBi2Nb2O9 ceramics by reaction controlled sintering

Reaction controlled sintering was applied to the fabrication of BaBi₂Nb₂O₉ (BBN) ceramics at lower temperature. A powder mixture of BaCO₃ and Nb₂O₅ was heated at 600 °C in a 1st step calcination to produce a binary precursor of BaNb₂O₆. The pre-heated powder was then mixed with a fixed amount of Bi₂O₃, which was subsequently pressed into a disk pellet. After a powder compact of the mixture was subjected to heating at 950 °C for 4 h, a BBN bulk sample with a relative density of 92% was successfully obtained. The low-temperature fabrication of dense BBN ceramics could be attributed to the inhibited formation of an intermediate phase of Ba₅ Nb₄O₁₅ and the production of submicron powder with an appropriate reactivity during a 1st step calcination.     

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.     

Gas sensitivity of ZnO-based ceramics to vapors of saturated monohydric alcohols

The sensitivity of electrical conductivity of ZnO-based ceramics to vapors of saturated monohydric alcohols was investigated. Its interconnection with physicochemical parameters of alcohols: molecular mass, entropy, Gibbs energy, enthalpy, the bond breaking energy of С–О and О–Н molecular bonds was analyzed.     

New solution method to produce high performance thermoelectric ceramics: A case study of Bi-Sr-Co-O

Bi₂Sr₂Co_1.8O_x ceramics have been synthesized through a solution method involving the addition of polyethyleneimine as coordinating agent for the metallic cations. From these powders, bulk sintered materials have been prepared. Microstructure has been studied by means of scanning electronic microscopy (SEM) and it has shown that samples are mainly composed by the thermoelectric phase, with very small amounts of secondary phases. Electrical resistivity measurements showed very small values (around 21 mΩ cm at room temperature), nearly constant with temperature, while thermopower increases rapidly to values higher than 200 μV/K at 650 °C. Power factor value at 50 °C is about 0.08 mW/K² m and 0.20 at 650 °C, which makes this ceramic a potential material for power generation applications.     

Investigation of the crystal structure and electrical properties of La3+-doped SrBi2Ta2O9 ceramics

The layered-perovskite ferroelectric ceramics of La³⁺-doped SrBi₂Ta₂O₂ (SBT), with the chemical formula of SrBi_{(2 - x)}La _x Ta₂O₉ (SBLT), have been prepared by the conventional mixed-oxide method. The effect of substitution of La³⁺ for Bi³⁺ in the crystal structure and electrical properties of SBT ceramics was explored with the aid of X-ray diffraction, (T) curve and ferroelectric hysteresis loop measurements. The electrical properties such as dielectric constant () and remanent polarization (P _r) showed a dependence on the crystal structure, and both reached maxima of 243 and 25 C cm^–2, respectively, with 6 at % La³⁺ substitution, accompanying the greatest structure change. Theoretical considerations were presented to suggest that the atomic displacements and the crystal deformation implied by the crystal structure change are responsible for the improvement of electrical properties. On the other hand, degradation of fatigue resistance was observed in SBLT ceramics, which is believed to be caused by the chemical environment change of the perovskite layers arising from La³⁺ substitution on Bi³⁺ sites.     

氧化铋掺杂氧化铈纳米材料的合成及其导电性

本实验利用聚乙烯醇(PVA)为聚合剂进行了氧化铋掺杂氧化铈氧离子导电体合成与导电性研究.通过粉末X射线衍射对合成材料进行了相分析,并利用交流阻抗方法测试,分析了试样的导电性.研究结果表明,通过PVA的聚合作用能在较低温度下(500℃)有效地合成出高纯的氧化铈纳米晶固溶体;氧化铋掺杂量在5%-15%(摩尔含量)范围内时,氧化铈的氧离子导电性随掺杂量的增加而增大;选用适当的烧结升温/降温速度能获得晶粒小于100nm的块体材料,并能有效地提高材料的导电性.     

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.     

Electron microscopic observation of rapidly cooled ZrO2-3 mol% Sm2O3 from the melt

Electron microscopic observation was made on ZrO₂-3 mol % Sm₂O₃ specimens prepared from the melt using two different cooling rates, namely rapid quenching using a hammer-anvil apparatus and free cooling on a water-cooled copper hearth. The observed microscopic features, such as fully tetragonal grains with parallel twins or herringbone structure, anti-phase boundary contrast in a dark-field image, tweed structure, etc., were found to be quite similar to those observed in similarly prepared ZrO₂-3 mol % Y₂O₃ specimens. It was specifically noted that the tweed structure, which requires atomic diffusion, was not suppressed by the rapid quenching, indicating a very fast growth rate. Trace analysis was also conducted on the tweed structure observed in freely cooled specimens.     

Sm_2O_3掺杂CeO_2纳米材料的电子顺磁共振研究

利用溶胶-凝胶法制备Sm2O3掺杂CeO2的电解质材料。通过粉末X射线衍射谱对所制备的电解质材料进行平均晶粒尺寸和晶格常数分析,并利用电子顺磁共振仪进行测试,分析样品的电子顺磁共振特性。结果表明:所制备的粉末样品晶粒尺寸较小、具有立方萤石型结构,而且Sm2O3掺杂CeO2的固体电解质材料有缺陷结构,随焙烧温度越高,缺陷结构越多;其次不同比例的Sm3+掺入CeO2后,材料中缺陷结构也有很明显的变化。     

Carbonate coprecipitation synthesis of Sr- and Mg-doped LaGaO3

A carbonate coprecipitation synthesis, simple and easily scalable to industrial level, has been successfully applied to produce Sr- and Mg-doped LaGaO₃. The thermal evolution shows that the main perovskite phase crystallizes already at 1000 °C. Samples sintered at 1400 °C for 10 h have a relative density of 93% and an electrical conductivity of 7.7 ? 10^− 2 S cm^− 1 at 800 °C, similar to the one reported for solid state synthesis. The presence of small amounts of secondary phases (about 17%) such as LaSrGaO₄ and LaSrGa₃O₇ does not seem to deeply affect the electrical properties of the final material.     

Dielectric Relaxation and Conductivity of Ba(Mg1/3Ta2/3)O3and Ba(Zn1/3Ta2/3)O3

The frequency dependent dielectric properties of barium magnesium tantalate(BMT),Ba(Mg_(1/3)Ta(2/3))O_3 and barium zinc tantalate(BZT),Ba(Zn_(1/3)Ta_(2/3))O_3 synthesized by solid state reaction technique have been investigated at various temperatures by impedance spectroscopy.BMT and BZT possess cubic structure with lattice parameter a = 0.708 and 0.451 nm,respectively.The resonance peaks due to dielectric relaxation processes are observed in the loss tangent of these oxides.The relaxation in the samples is polydispersive in nature.The temperature dependence of dc conductivity,the most probable relaxation frequency(ω_m) obtained from tanδ vs logw plots and ω_m obtained from imaginary parts of the complex electrical modulus vs logw plots follow the Arrhenius behavior.According to these Arrhenius plots the activation energies of BMT and BZT are about 0.54 and 0.40 eV,respectively.Thus the results indicate that samples are semiconducting in nature.The frequency-dependent electrical data are analyzed in the framework of conductivity and electric modulus formalisms.Both these formalisms show qualitative similarities in relaxation time.Our study points that for complex perovskite oxides with general formula A(B'B")O_3,the dielectric properties significantly depend on the atomic radii of both A and B type cations.BMT and BZT exhibit enhancement in dielectric property compared to their niobate counterparts.They may find several technological applications such as in capacitors,resonators and filters owing to their high dielectric constant and low loss tangent.     

X-ray photoelectron spectroscopy and electrical properties studies of La2O3-doped strontium titanate ceramics prepared by sol-precipitation method

X-ray photoelectron spectroscopy has been used to investigate the existence of Ti³⁺ on the surface of La₂O₃-doped strontium titanate and to determine its surface characteristics. The surfaces, having Sr/Ti ratios significantly varying from the stoichiometric ratio, revealed the presence of carbon and suggested the presence of hydroxyl groups on the surface, whose concentration largely decreased in the bulk. Ti³⁺ species existed as a function of the sintering conditions and were detected on the surface of (La, Sr)TiO₃ sintered in air or in N₂ by natural cooling. These samples had a lower electrical resistivity, especially when sintered in a N₂ atmosphere. The surfaces of air oxidized SrTiO₃ and quenched from high temperature contained no detectable amount of Ti³⁺, resulting in higher resistivity. However, the N₂-sintered samples were dark blue in color and exhibited lower resistivity, semiconductivity, and lower valence oxidation state Ti existed when sintered above 1350°C.