Lithium ion conduction in Li5La3Ta2O12 and Li7La3Ta2O13 garnet-type materials

Electrical properties of the lithium garnets Li₅La₃Ta₂O₁₂ (L5LTO) and Li₇La₃Ta₂O₁₃ (L7LTO) are reported over a wide frequency range from 10 MHz to 0.1 Hz at different temperatures. The structural properties are characterized by powder X-ray diffraction, Scanning electron microscopy with energy dispersive X-ray spectroscopy and Fourier transformation Infrared spectroscopy. By means of the frame work of classical brick layer model (BLM) and of a finite element approach, the ion transport properties of grain and grain boundary for the lithium garnets were analyzed. The specific grain conductivity of 5.0?×?10^?6?S/cm at 40 °C is found for both lithium garnets. Specific grain conductivities and grain boundary conductivities are thermally activated, with activation energies found to be in the range of 0.55–0.61 eV. The total conductivity is found to be depending on the ion conduction of grain boundary. The information on the fraction of contact area α_contact between grains <0.25 is obtained by the finite element approach for Li₇La₃Ta₂O₁₃.     

Grain Boundary Defect Chemistry of Acceptor-Doped Titanates: High Field Effects

The field enhanced average conductivity in grain boundary space charge depletion layers in acceptor-doped SrTiO₃ ceramics was investigated by impedance analysis in the time domain. The dependence of the grain boundary conductivity on the acceptor concentration, the temperature and the field dependence are discussed and interpreted in terms of a Schottky diffusion model combined with the influence of accumulated oxygen vacancies at the GB interface.     

Structural and electrical studies of Ba5LaTi3V7O30 compound

The ferroelectric ceramic Ba₅LaTi₃V₇O₃₀ has been synthesized by solid-state reaction technique. Preliminary X-ray structural analysis confirmed a single-phase formation (orthorhombic crystal system) of the compound. Surface morphology of the compound was studied by scanning electron microscopy (SEM). Detailed studies of electrical properties (i.e., dielectric constant, loss tangent, ac and dc conductivity) as a function of temperature (RT - 773?K) at four different frequencies, 1?kHz, 10?kHz, 100?kHz and 1?MHz show ferroelectric—paraelectric phase transition of the compound. The impedance spectra show two distinctly separated regions in wide temperature range corresponding to grain boundary and grain interior contributions. The activation energy has been evaluated from ac conductivity and dc conductivity following Arrhenius equation is 0.15?eV at 1?MHz and 0.28?eV, respectively. The temperature dependence of electrical conductivity shows that the conductivity increases with increase in temperature suggesting that the compounds have a negative temperature coefficient of resistance (NTCR) behaviour. The conductivity pattern shows that it is strongly frequency dependent and obeys Jonscher’s power relation.     

Separation of the bulk and grain boundary contributions to the total conductivity of solid lithium-ion conducting electrolytes

The transport properties of lithium-ion conducting Li_3xLa_2/3-xTiO₃ are studied for bulk and grain-boundary effects. This paper introduces a procedure for investigating bulk and grain-boundary polarization contributions using electrochemical impedance spectroscopy (EIS) and subsequent analysis via the distribution function of relaxation times (DRT) [1]. The frequency range of impedance spectroscopy is extended up to 120 MHz to resolve all conductivity contributions occurring in a polycrystalline solid electrolyte. Intra grain (bulk) and inter grain (grain boundary) conductivity contributions are separated using (i) a systematic variation of solid electrolyte contacting, (ii) two different solid electrolyte microstructures and activation energies were determined using adequate equivalent circuit models. Finally, these results are supported by SEM analysis, revealing different grain size distributions and different contents of inhomogeneities in Li_3xLa_2/3-xTiO₃ solid electrolytes sintered at 1400°C and at 1450°C.     

Interface mediated transport properties in n-type SrTiO3 : Induced dipole alignment at oxide grain boundaries

Low temperature potentiometry and capacitance measurements based on noncontact atomic force microscopy were used to quantify local properties due to grain boundaries at a 0.05 wt.% Nb-doped SrTiO₃ [001] surface. Local I-V curves were constructed by combining potential steps and transport currents measured at individual grain boundaries (GBs) under different lateral biases. The GBs exhibit a positive temperature coefficient of resistivity (PTCR) effect. A comparison of transport properties and calculations suggest that SrTiO₃ grain boundaries undergo a non-polar to polar state phase transition induced by the large electric field associated with the boundary charge. This is supported by the temperature dependence of the barrier height and the boundary charge obtained by numerical simulation of I-V curves using a double Schottky barrier model. The built-in potential associated with the boundary was directly imaged with frequency-modulated Kelvin probe force microscopy at different temperatures and the results support the previous conclusion.     

Ni-Cu-Zn Ferrites for low temperature firing: II. Effects of powder morphology and Bi2O3 addition on microstructure and permeability

The morphology of Ni-Cu-Zn ferrite powders obtained by milling of a calcined raw materials mixture strongly effects the densification behavior during sintering at 900^∘C. In order to obtain dense samples sub-micron powders with enhanced reactivity are required. The addition of Bi₂O₃ as sintering additive is beneficial: the density of samples sintered at 900^∘C increases with the bismuth oxide concentration up to 0.75 wt.%. The process of liquid phase sintering was studied by dilatometry. The grain size of the sintered samples slightly increases for 0.25 wt.% Bi₂O₃ compared to bismuth-free samples, whereas for 0.3–0.5 wt.% Bi₂O₃ additions bimodal grain growth is observed with a significant fraction of very large grains. For > 0.5 wt.% Bi₂O₃ a homogeneous coarse-grained microstructure is obtained. The permeability increases for small bismuth oxide additions, but decreases for a Bi-oxide content of more than 0.5%. Maximum permeability of μ_i = 900 is observed for intermediate Bi₂O₃ concentrations. PACS codes: 75.50 Gg; 81.20 Ev; 81.40 Rs     

Arc erosion characteristics of Cu-W contact at load current range in SF6 gas

Development of SF₆ gas-insulated switches that have a long service life and are highly reliable at medium voltage ratings require arc erosion of contacts in SF₆ gas to be decreased. The effects of SF₆ gas pressure and magnetic field for arc blow-out on erosion were studied experimentally in detail using sintered Cu-W contacts. The test current, SF₆ pressure and magnetic field were 100 to 400 A, 0.1 to 0.6 MPa and 0 to 50 mT, respectively. The results show that the arc erosion rate increased linearly with the SF₆ pressure. The magnetic field effectively reduced anode erosion (i.e., the application of a mere 50 mT lowered the erosion rate to 1/3 to 1/4). These phenomena may be attributed, respectively, to the increase in evaporation rate according to the shrinkage of arcing spot areas caused SF₆ pressure and a decrease of the evaporation rate correlating to high-speed movement of the arcing spot on the anode by the magnetic field. However, the cathode erosion was insensitive to the magnetic field. The influence of both W grain size and composition ratio, Cu:W, on the erosion rate was also studied. The smaller W grain at Cu content of 50 to 70 wt.% was found to be best for suppression of erosion under the present conditions. Further, the increase of N₂ mixture ratio to SF₆ under constant total gas pressure greatly decreased contact erosion. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 118 (1): 41–51, 1997     

Mixed Electronic-Ionic Conductivity of Cobalt Doped Cerium Gadolinium Oxide

The effect of small amounts (<5 mol %) of cobalt oxide on the electrical properties of cerium oxide solid solutions has been evaluated. Ce_0.8Gd_0.2O_2-x (CGO) powder with an average crystallite size of 20 nm served as a model substance for the electrolyte material with a high oxygen ion conductivity and low electronic conductivity in its densified state. Doping the CGO powder by transition metal oxides (MeO) with concentrations below 2 mol % did not change the ionic conductivity nor the electrolytic domain boundary. After long sintering times (2 h) at temperatures above 900°C, MeO and CeO₂ form solid solutions. However, short sintering times or high dopant concentrations lead to an electronic conducting grain boundary phase short circuiting the ionic conductivity of the CGO grains. Choosing proper doping levels, sintering time and temperature allows one to tailor mixed conducting oxides based on CGO. These materials have potential use as electrolytes and/or anodes in solid oxide fuel cells and ion separation membranes.     

Study on Preparation of Quartz Ceramics Toughened with Mineralizer

Abstract

Quartz ceramics have excellent properties such as low thermal conductivity, low expansion coefficient, high temperature resistance and thermal stability, but low toughness. The quenching method of quartz ceramic is as follows: (1) A hard phase is formed in the quartz ceramic. (2) Improve the surface coating. (3) Short fiber reinforcement. (4) The graphite particles are dispersed and quenched. (5) Have silicone resin reinforcer. (6) Improve mineralizers. In order to improve the toughness of quartz ceramics, a hardening mineralizer is selected in this experiment. In this experiment, quartz is used as the main raw material, and a mineralizer is selected as the aluminate, feldspar and Al₂O₃ powder cement. Quartz ceramics are prepared by molding. Adding 10% Al₂O₃ powder, adding Al₂O₃ powder can improve the flexural strength of quartz ceramics, and the flexural strength of quartz ceramics can reach 10?MPa. SEM analysis shows that the addition of Al₂O₃ can inhibit the grain boundary motion speed better and prevent grain growth, enhancement and enhancement. XRD analysis shows that the addition of aluminate cement, feldspar and calcium oxide may be beneficial to the conversion of quartz to cristobalite and the addition of Al₂O₃ to the conversion of quartz to phosphorus quartz.     

Electron-Ion Transport in ZrO2-Y2O3-CeO2 Ceramics

Simultaneous conduction of oxide ions and electrons in solid ceramic systems provides the capability for oxygen transport under a concentration gradient without the need for an externally applied electric field. In the present study, ionic transference numbers have been measured in the ZrO₂-5.8%Y₂O₃-10%CeO₂ system by open circuit Emf measurements involving different metal/metal oxide electrodes. In order to correlate the ionic transference number with grain size, high-density ceramic discs of different grain sizes (50 nm–5 m) were prepared by sintering pressed powders at various temperatures and times. Hydrothermal synthesis was used to prepare nanocrystalline powders of the above material with uniform crystallite size (10 nm) and chemistry. Emf measurements on the samples suggested both ionic and electronic transport, the ionic transference number decreasing with increase in the grain size. This observation was attributed to an increase in the amount of continuous crystalline grain boundary phase in the ceramics as the grain size increased. The presence of crystalline silicate and zirconate phases in the grain boundary region was confirmed by electron microscopic imaging combined with microanalysis. In the large grain (5 m) ceramics, the ionic transference number decreased linearly with temperature. As the grain size decreased, a maximum occurred in the ionic transference number vs. temperature curve. This maximum became more pronounced at smaller grain sizes. Better grain-grain contact and the doping effect of trivalent Ce in the grain boundary core are proposed to explain this observation.     

Synthesis of nanocomposites of PMN-PT-BT with metal oxides via surface modification

Low-temperature-sinterable PMN-PT-BT [0.96 (0.91Pb(Mg_1/3Nb_2/3)O₃-0.09PbTiO₃)-0.04BaTiO₃] powder was first prepared by the modified mixed oxide method and then metal (M = Cu, Mg, Ag) oxides were introduced as their nitrate salts. Precalcined PMN-PT-BT/MO composite powders were surface modified with the magnesia sol to suppress diffusion of Ag or metal oxides. Such prepared composite powders were sintered > 98% T.D. at 850–900^∘C and showed homogeneous microstructures with <100 nm Ag or metal oxide particles. Nanoparticles were located mostly in grains and some on grain boundaries. Grain growth was substantially inhibited and resulted in grain size of ∼2 μm. The nanocomposites of PBT/Ag and PBT/MgO showed substantially improved sintered densities and dielectric properties at sintering temperature below 1000^∘C, but the PBT/CuO composite was hardly affected. The PBT/Ag composites treated with the MgO sol showed good handling strength of MOR > 120 MPa. The proper amount of the magnesia sol for surface modification seemed to be 0.5–1.0 wt.     

Effect of doped Ni2+ on the dielectric properties of NiO-BaTiO3 composites

NiO-BaTiO₃ composites were prepared by sintering BaTiO₃ together with NiO in air at 1300°C. Microstructure and morphology of the composites were detected by XRD and SEM, and the dielectric properties were measured by LCZ meter. The results indicate that the perovskite phase is formed in fact in status of solid solution doped with Ni²⁺, although only a small amount of Ni ions can dissolve into the perovskite phase. Ni doping decreases the formation temperature of the composite without inhibiting the grain growth of the crystalline phase. The dielectric constant decreases sharply and the dielectric loss decreases smoothly with increasing Ni²⁺ below NiO addition of 0.5 wt.%. When NiO addition increases above 0.5 wt.%, the dielectric constant and loss correlate with mixing rule of the two phases. Meanwhile, the replacement of Ni²⁺ for Ti⁴⁺ decreases the Curie temperature of perovskite phase by 30°C.     

Impedance spectroscopy studies of K0.5Bi0.5TiO3

Lead free Potassium bismuth Titanate K_0.5Bi_0.5TiO₃ (KBT) was prepared by high temperature solid state reaction method in a closed crucible with excess KBT powder around the samples. A room temperature study of XRD confirms, single phase formation with tetragonal structure .Grain and grain boundary conduction is observed from complex impedance spectrum at high temperatures (425°C) by the appearance of two semicircular arcs. The Cole-Cole plots of impedance spectrum consisted of a Circular arc followed by a semicircular spur indicate that the dielectric phenomenon of KBT is due to conductive grain boundaries. The temperature variation of grain resistance and grain boundary resistance is observed with the activation energies. The presence of non-Debye type multiple relaxations has been confirmed by complex modulus analysis. The dielectric data obtained from impedance measurements, indicates broad dielectric peaks around 380°C. The ferroelectric nature confirmed from hysteresis plot. The DC Conductivity results indicate activation energy 0.54 eV below 400°C and 0.85 eV above 400°C. The AC conductivity values and electric modulus values are computed from the impedance data. The activation energies of AC conductivity have observed to decrease with decrease in frequencies.     

高强高导CuCr合金的显微组织与性能研究

采用粉末冶金烧结挤压工艺成功制备出高强高导Cu₁.5Cr合金材料,对合金的显微组织、物相组成、力学与电学性能等进行了研究。结果表明,合金基体组织晶界处存在富铜铬的未溶相。Cu₁.5Cr合金抗拉强度为670 MPa,延伸率为11%,软化温度为500℃,导电率为86%IACS。合金断口呈现出大量的延性韧窝,断裂方式为典型的塑性断裂。     

Preparation, microstructure and electrical properties of Li1.4Al0.4Ti1.6(PO4)3 nanoceramics

NASICON-type Li_1.4Al_0.4Ti_1.6(PO₄)₃ solid electrolytes were prepared by various processes, such as crystallization of glasses, spark plasma sintering (SPS) and conventional sintering process from nanosized precursor powders synthesized by a sol–gel route. The experimental results showed that grain size and relative density were the main factors determining the ionic conductivity of the bulk materials. The SPS technique produced ceramics with nearly 100% of the theoretical density. Maximum room temperature conductivities, 1.39?×?10^?3 S cm^?1 and 1.12?×?10^?3 S cm^?1 of grain boundary conductivity and total conductivity, respectively were obtained which were the highest values for Li⁺ inorganic oxide conductors as reported. Crystallization of ceramics from a glass was also certified as a favorable route to fabricate a bulk material with high conductivity.     

The effect of Co addition on the electrical conductivity of Sr- and Mg-doped LaAlO3

Co was added to see its effect on the electrical conductivity of Sr- and Mg-doped LaAlO₃ (La_0.9Sr_0.1 Al_0.9Mg_0.1O₃, LSAM). Electrical conductivities of La_0.9Sr_0.1(Al_0.9Mg_0.1)_{1− x}Co_xO₃ (LSAMC) for x = 0–0.20 were measured using 2-probe a.c. and 4-probe d.c. method at temperature between 300 and 1300^∘C in air, and as a function of Po ₂ (1–10⁻¹⁵ atm) at 1200^∘C. Electrical conductivities in air increased with increasing Co content, while their activation energy decreased. From the impedance spectroscopy analysis, it was found that both the grain and the grain boundary conductivities of LSAMC samples increased rapidly with Co-addition. LSAMC samples were oxygen ion conductors in low Po₂ and mixed conductors in high Po ₂ up to x = 0.1 just like LSAM. With Co-doping, p-type conductivities increased, however, ionic conductivities remained nearly constant.     

Liquid phase effect of La2O3 and V2O5 on microwave dielectric properties of Mg2TiO4 ceramics

Dielectric ceramics of Mg₂TiO₄ (MTO) were prepared by solid-state reaction method with 0.5–1.5 wt.% of La₂O₃ or V₂O₅ as sintering aid. The influences of La₂O₃ and V₂O₅ additives on the densification, microstructure and microwave dielectric properties of MTO ceramics were investigated. It is found that La₂O₃ and V₂O₅ additives lowered the sintering temperature of MTO ceramics to 1300 °C and 1250 °C respectively, whereas the pure MTO exhibits highest density at 1400 °C. The reduction in sintering temperature with these additives was attributed to the liquid phase effect. The average grain sizes of the MTO ceramics added with La₂O₃, and V₂O₅ found to decrease with an increase in wt%. The dielectric constant (ε_r) was not significantly changed, while unloaded Q values were affected with these additives, and the values were in the range of 92,000–157,550 GHz and 98,000–168,000 GHz with the addition of La₂O₃ and V₂O₅, respectively. The dielectric properties are strongly dependent on the densification and the microstructure of the MTO ceramics. The decrease in Q×f _o value at higher concentration of La₂O₃ and V₂O₅ addition was owing to inhomogeneous grain growth and the liquid phase which is segregated at the grain boundary. In comparison with pure MTO ceramics, La₂O₃ and V₂O₅ additives effectively improved the densification and dielectric properties with lowering of sintering temperature. The proposed loss mechanisms suggest that the oxygen vacancies and the average grain sizes are the influencing factors in the dielectric loss of MTO ceramics.     

Characterization of PT ferroelectric thin films on porous silica for pyroelectric IR detectors

Ferroelectric PbTiO₃ thin films were deposited on Pt/DS/PS/SiO₂/Si substrates by sol–gel technique. Porous silica (PS) thin film was used as thermal-insulation layer and dense silica (DS) thin film was a buffer layer to reduce surface roughness of PS layer. Root mean square surface roughness can be effectively reduced from 9.7 to 3.5 nm after PS buffer layer was prepared. The average grain size of PT thin films decreased slightly with increasing thickness of porous silica. Dielectric constant of PT increased from 107 to 171 at 1 KHz as thickness of PS layer increased from 0 to 2,000 nm. PT thin film prepared on 2,000 nm porous silica exhibited good dielectric property. The leakage current density was less than 1.6?×?10^-6 A/cm² when the applied electrical field was 200 kV/cm. The composite film is suitable for preparing pyroelectric IR detectors.     

Nonstoichiometry and Electrical Conductivity of Nanocrystalline CeO{2 - x}

We synthesized dense CeO polycrystals of 10 nm grain size and characterized their electrical conductivity, in order to determine whether the defect properties of nanocrystalline solids fundamentally differ from those of conventional materials. The nanocrystals exhibit enhanced electronic conductivity, greatly reduced grain boundary impedance, and a heat of reduction more than 2.4 eV lower per oxygen vacancy compared to their coarse-grained counterparts. We propose that defect formation at low energy grain boundary sites is responsible for these properties, and that nanocrystalline oxides represent bulk materials possessing the defect thermodynamics of interfaces.     

Composition and structure of calcium aluminosilicate microspheres

The composition was studied of calcium aluminosilicate microspheres of three morphological types in high-calcium fly ash from combustion of brown coal from the Kansk-Achinsk basin in slag-tap boilers at temperatures from 1400 to 1500°С and sampled in the first field of electrostatic precipitators at the Krasnoyarsk Cogeneration Power Station no. 2 (TETs-2). Gross compositions and the composition of local areas were determined using a scanning electron microscopy technique and an energy-dispersive analysis with full mapping of globules. With a high content of basic oxides O _ох (68 to 79 wt %) and a low content of acid oxides K _ох (21 to 31 wt %), type 1 microspheres are formed. They consist of heterogeneous areas having a porous structure and crystalline components in which the content of CaO, SiO₂, or Al₂O₃ differs by two to three times and the content of MgO differs by seven times. With a lower content of O _ох (55 to 63 wt %) and an elevated content of K _ох (37 to 45 wt %), type 2 microspheres are formed. They are more homogeneous in the composition and structure and consist of similar crystalline components. Having a close content of O _ох (46 to 53 wt %) and K _ох (47 to 54 wt %), type 3 microspheres, which are a dense matter consisting of amorphous substance with submicron- and nanostructure of crystalline components, are formed. The basic precursor in formation of high-calcium aluminosilicate microspheres is calcium from the organomineral matter of coals with various contribution of Mg, Fe, S, or Na from the coal organic matter and Al, Fe, S, or Si in the form of single mineral inclusions in a coal particle. On the basis of the available data, the effect was analyzed of the composition of a CaO–MgO–Al₂O₃–SiO₂–FeO system on the melting and viscous properties of the matter in microspheres and formation of globules of different morphology. The results of this analysis will help to find a correlation with properties of microspheres in their use as functional microaggregates in cement or polymeric composite materials, or in the production of ceramic membranes or zeolite sorbents.