Glass dispersion favours ionic conduction in 6Li2SO4-4Li2CO3 composite solid electrolyte

The effect of a dispersion of 7Li₂O-3B₂O₃ glass on the electrical conductivity of 6Li₂SO₄-4Li₂CO₃ eutectic has been studied. The samples were prepared by two different methods. With the dispersion of glass into the crystalline matrix a prominent increase in the conductivity has been observed. The results have been explained in the light of dispersed phase theory using microstructural evidence. These results would provide a new approach for achieving an enhancement in the ionic conductivity of solid electrolytes.     

Order-disorder phenomena in oxides with rock salt structures: the system Li2TiO3-Mg0

Li₂TiO₃, which belongs to the family of rock salt superstructure phases, undergoes an order-disorder phase transition at 1213° C. It forms solid solutions with MgO and the temperature of the order-disorder change falls increasingly rapidly with increasing MgO content; the ordered solid solutions could not be prepared beyond 40 mol % MgO. Up to 20% MgO, the transition may be observed as a DTA heat effect and is probably first order. At 25% MgO the transition is second order; no DTA heat effect occurs and, by X-ray diffraction, the order-disorder change occurs, reversibly and continuously, over a range of several hundred ° C. For 25% MgO, the disorder, , is given by =exp[–m(T _c–T)] whereT _c is the critical temperature, above which only short range order exists, andm is a constant. The order, , is determined from the relative intensity of the (0 0 2) superstructure reflection. The mechanisms of the order-disorder processes are discussed and a method of studying the kinetics is indicated. It is likely that many other oxide phases which have rock salt superstructures will exhibit order-disorder phenomena at high temperatures.     

On brittle-to-ductile transition in covalent diamond-like and ionic rock salt structure solids

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Structural and dielectric properties of Li2O-doped TiO2

The dielectric properties of the system Li–Ti–O have been exploited in the frequency range 20 Hz–1 MHz in order to obtain permittivity data of materials having high-κ′ and low loss. Doping of titanium dioxide with lithium oxide acts as a strong promoter of the anatase to rutile phase transition and it may reduce the phase transition temperature (915 °C) by more than 100 °C, possibly due to induced oxygen concentration disorders in the ternary Li–Ti–O system. For TiO₂:Li₂O molar ratios of 98.92:1.08 and calcination temperature of 950 °C the resulting material exhibits high-κ′ and low-loss permittivity properties with lack of interfacial polarization effects. Its dielectric response is superior compared to pure (undoped) rutile as obtained by calcination at much higher temperatures (1180 °C).     

Li2O-SiO2-V2O5-P2O5体系的锂快离子导体的研究

运用混料均匀设计方法,设计了四元体系Li2O-SiO2-V2O5-P2O5的实验配方,找出其中电导率最佳的区域以及电导率随配方的分布变化规律.试验验证点的实测值与预测值相当,得到的室温电导率达到10-5S/cm.     

Structural, dielectric and electrical properties of Li2Pb2La2W2Ti4Nb4O30 ceramic

Li₂Pb₂La₂W₂Ti₄Nb₄O₃₀ complex ferroelectric oxide was prepared by using a high-temperature solid-state reaction method (calcination temperature, ~1100 °C and sintering temperature, ~1150 °C). Room temperature preliminary structural analysis shows formation of a single-phase compound. The nature of microstructure (i.e. grain distribution, presence of voids, grain size, etc) recorded using scanning electron microscope (SEM) clearly suggests the formation of high quality and density of pellet samples. Studies of temperature dependence of dielectric constant, tangent loss and polarization show the existence of ferroelectric phase transition in the material at high temperature (307 °C). Detailed studies of temperature dependence of electrical parameters (i.e. impedance (400?475 °C), modulus, conductivity, etc) of the material clearly suggest a strong correlation between its microstructure (i.e. bulk, grain boundary, etc) and electrical properties. The nature of temperature variation of d.c. conductivity showed an Arrhenius behaviour of the material. A signature of ionic conductivity in the material was observed in its a.c. conductivity spectrum. The nature of frequency dependence of a.c. conductivity of the material can be explained by Jonscher’s universal power law. Electrical transport properties of the material show existence of non-exponential type of conductivity relaxation.     

A new microwave dielectric ceramics for LTCC applications: Li2Mg2(WO4)3 ceramics

A novel microwave dielectric ceramics Li₂Mg₂(WO₄)₃ (LMW) for low-temperature co-fired ceramics (LTCC) application were prepared by the conventional solid-state sintering method. Densification, phases, microstructure and microwave dielectric properties of the Li₂Mg₂(WO₄)₃ ceramics were investigated. The optimal sintering temperature of dense Li₂Mg₂(WO₄)₃ ceramic approximately ranges from 825 to 875 °C for 3 h. The ceramic specimens fired at 875 °C for 3 h exhibits excellent microwave dielectric properties: ε _r  = 7.72, Q × f = 29,600 GHz (f = 6.0 GHz), and τ _f  = ?15.5 ppm/°C. Moreover, the Li₂Mg₂(WO₄)₃ ceramics has a chemical compatibility with Ag during cofiring, which makes it a promising ceramic for LTCC technology application.     

Low temperature sintering and microwave dielectric properties of Li2ZnSiO4 ceramics with ZB glass

The influence of zinc borate (ZB) glass on densification, phase composition, microstructure and microwave dielectric properties of Li₂ZnSiO₄ ceramics has been investigated by using X-ray diffraction, scanning electron microscopy and Advantest network analyzer. Undoped Li₂ZnSiO₄ ceramics exhibited good microwave dielectric properties of ε _r  = 5.8, Q × f = 14,700 GHz and τ _f  = ?96.6 ppm/°C. When ZB glass was added, the sintering temperature of Li₂ZnSiO₄ ceramics was effectively reduced to 950 °C. Addition of 25.wt% ZB glass to Li₂ZnSiO₄ ceramics sintered at 950 °C showed excellent dielectric properties of ε _r  = 5.5, Q × f = 10,800 GHz (f = 6.8 GHz) and τ _f  = ?47.2 ppm/°C. Moreover, the material was compatible with Ag electrodes, making it a very promising candidate material for LTCC applications.     

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).     

溶胶-凝胶法合成锂离子筛前驱体LiMn2O4的研究

用溶胶 凝胶法、以柠檬酸和乙二醇作为聚合反应的单体合成了正尖晶石结构LiMn2 O4的前驱体 ,研究了反应物摩尔比、pH值及焙烧温度对材料性能的影响 ,并通过XRD、IR和SEM等方法研究了柠檬酸螯合法合成正尖晶石结构LiMn2 O4 的溶胶 凝胶过程 ,探讨了反应机理。研究表明白 ,在Li/Mn摩尔比为 0 6、pH值为 3 0及焙烧温度为 6 0 0℃时 ,合成的正尖晶石结构LiMn2 O4 的前驱体具有较好的晶粒结构 ,其一次粒子直径大多在 1 0 0nm以内。     

structure and transport properties of Li1-2xCo1+xVO4 lithium ionic conductors

Li_1-2xCo_{1 +x} VO₄ (0 ≤x ≤ 0.25) spinel solid solutions were synthesized and characterized by x-ray diffraction and IR spectroscopy. The materials were found to have a cubic structure in the composition range 0 ≤x ≤ 0.1 and an orthorhombic structure forx> 0.1. The observed lattice distortions were shown to correlate with Co content. The conductivity of the solid solutions was measured as a function of temperature and oxygen partial pressure. The ionic and electronic (n andp) conductivities were determined. The conduction in the solid solutions was shown to be dominated by Li⁺ ions.     

Crystal structure and ionic conductivity of Li14Zn(GeO4)4 and other new Li+ superionic conductors

This paper reports the synthesis and characterization of a number of new Li⁺ superionic conductors with the type formula Li_16?2xD_x(TO₄)₄, where D is a divalent cation (Mg²⁺ or Zn²⁺), T is a tetravalent cation (Si⁴⁺ or Ge⁴⁺), and 0 < x < 4. One of these materials, Li₁₄Zn(GeO₄)₄, has a resistivity of 8 ω-cm at 300°C, lower than that of any Li⁺-ion conductor so far reported. The structure of this compound, which we have named LISICON (for $\text{Li s}$uper$\text{io}$nic $\text{con}$ductor), has been determined by single-crystal x-ray analysis. The space group is Pnma, with cell parameters $\text{a}\text{=10.828}\text{A}\text{?}$, $\text{b}\text{=6.251}\text{A}\text{?}$, $\text{c}\text{=5.140}\text{A}\text{?}$, and z=1. The structure has a rigid three-dimensional network of Li₁₁Zn(GeO₄)₄. The three remaining Li⁺ ions have occupancies of 55 and 16%, respectively, at the 4c and 4a interstitial positions. Each 4c position is connected to two 4a positions and vice versa. The bottlenecks betweenthese positions have an average diameter that is larger than twice the sum of the Li⁺ and O^2? ionic radii, thus satisfying thegeometrical condition for fast Li⁺ -ion transport. Moreover, all four sp³ orbitals of the O^2? ion are shared by strong tetrahedral covalent bonds with the network cations. Therefore, the anion charge is polarized away from the interstitial Li⁺ ions, weakening the Li1bO bond and increasing the Li⁺-ion mobility.     

A co-precipitation technique to prepare BiNbO4, MgTiO3 and Mg4Ta2O9 powders

A simple co-precipitation technique has been used successfully for the preparation of pure, ultrafine, single phase BiNbO₄ (BN), MgTiO₃ and Mg₄Ta₂O₉. An aqueous sodium hydroxide or ammonium hydroxide and ammonium carbonate solution was used to precipitate these cations as hydroxides and carbonates simultaneously under basic conditions. These precursors on heating at 750 °C, produce the respective powders. For comparison, these compounds were also prepared by the traditional solid state method. The phase purity and lattice parameters were studied by powder X-ray diffraction (XRD). Particle size and morphology was studied by transmission electron spectroscopy (TEM).     

The CuI-ZnI2 system,Part I: Synthesis and ionic conductivity

Compositions from 90 m/o CuI-10 m/o ZnI₂ to 10 m/o CuI-90 m/o ZnI₂ have been synthesized and studied with differential scanning calorimetry (DSC), X-ray diffraction at room temperature and electronic and ionic conductivity measurements (25 to ～350°C). The compositions with $\text{≧40}\text{m}\text{/}\text{o}$ CuI are solid solutions at room temperature, while disproportionation occurs in the 10 to 30 m/o CuI materials. The electrical conductivities of compositions with $\text{≧60}\text{m}\text{/}\text{o}$ CuI change from mixed to ionic at ～150°C, corresponding to DSC transitions in the same temperature region. These conductivities are higher than that of pure CuI. The highest conductivity, for 80 m/o CuI-20 m/o ZnI₂ (1.8×10^?3 (θ cm)^?1 at 250°C), is about eight times higher than that of CuI.     

The use of image charges in the charge-simulation method: aparallel-plane dielectric plate covering a conductor

It is noted that, when applied to two dielectrics, the charge simulation method needs a number of additional charges with respect to the single dielectric case. This can strongly increase the time of computation. It is analytically shown that, if the geometry to be solved is a dielectric medium facing a parallel plane dielectric plate covering a conductor, the problem can be again treated with the charge-simulation method in one dielectric only. In this way calculations of electric fields have been performed for a case relevant to insulation tests at high voltages: a conducting sphere in contact with a dielectric plate coating a plane conductor     

Microwave dielectric properties of low temperature firing (Li1/2Nd1/2)WO4 ceramic

A new kind of low temperature sintering ceramic with composition of (Li_1/2Nd_1/2)WO₄ were prepared by solid state reaction method. The phase and structure of the ceramics were characterized by X-ray diffraction (XRD), scanning electron microscopy. The microwave dielectric properties of the ceramics were studied using a network analyzer. All the XRD patterns can be fully indexed as single-phase tetragonal structure (I41/n), with lattice parameters a = b = 5.25789 Å and c = 11.39124 Å. The ceramic sintered at 775 °C for 4 h exhibits a good microwave dielectric properties with permittivity about 16.1, Q × f about 4,210 GHz and TCF about 142 ppm/°C.