Glass formation domains and structural properties of nonconventional transition metal ion glasses

Glass formation domains and structural properties of some binary transition metal ion glasses based on nonconventional network formers Bi₂O₃ and PbO have been investigated. With the same network former, the glass formation domains depend on the transition metal ions. Homogeneous glasses with random network structure were obtained, as evidenced by the composition dependent density, molar volume and glass transition temperatures. Significant information about possible structural units in these glasses has been obtained from the IR spectra of these glasses.     

Fast ion conducting lithium glasses—Review

For the last few years fast ion conducting lithium glasses are being studied due to their potential use in advanced electrochemical devices. A number of glass systems containing oxides, sulphides and other lithium compounds prepared by both conventional cooling and rapid quenching techniques have been reported. In this paper we review the transport properties of lithium ion conducting glasses. The special features of the ionic conduction process have been highlighted and some experimental techniques to study transport properties have been described. Some of the common observations of the properties have been discussed and finally some important problems for future development have been pointed out.     

Anion conduction in fluorozirconate glasses

Fluorozirconate glasses have been prepared and their ionic conductivity measured as a function of composition and temperature. All compositions are good fluoride ion conductors with conductivities at 250°C in the 10^?6–10^?5 (Ω-cm)^?1 range and activation energies between 0.7 and 0.9 eV. The fluoride ion to metal ratio was varied in the ZrF₄/1bBaF₂/1bThF₄/1bNaF system by replacing ZrF₄and/or BaF₂ with NaF. When Na⁺ substitutes for Ba⁺² a systematic decrease in the conductivity, σ, and the activation energy, E_a, is seen. This is explained on the basis of a reduction of carriers and on the modification of the network by Na⁺ ions. No systematic variation in σ or E_a were seen when Na⁺ replaces Zr⁺⁴. A change in slope of the log σ vs 1/T plot was seen at the glass transition temperature in La-containing glasses.     

Fast ionic lithium conduction in solid lithium nitride chloride

Lithium nitride chloride (Li_1.8N_0.4Cl_0.6) crystallizes in a defect anti-fluorite structure with 10% of the lithium sites being vacant. Its electrical conductivity and thermodynamic stability have been investigated in the temperature range from 25 to 400° C. Lithium ions are the predominant charge carriers, yielding a conductivity temperature product of σ T = 7.456 × 10⁴ exp(?0.49₅ eV/kT) $\text{Ω}{}^{\mathrm{?1}}$ cm^?K. The electronic contribution to the total conductivity is smaller by a factor of less than 10^?4. The material is thermodynamically stable against pure metallic lithium and has a decomposition voltage larger than 2.5 V.     

Construction of nanostructures for selective lithium ion conduction using self-assembled molecular arrays in supramolecular solids

Abstract

In the development of innovative molecule-based materials, the identification of the structural features in supramolecular solids and the understanding of the correlation between structure and function are important factors. The author investigated the development of supramolecular solid electrolytes by constructing ion conduction paths using a supramolecular hierarchical structure in molecular crystals because the ion conduction path is an attractive key structure due to its ability to generate solid-state ion diffusivity. The obtained molecular crystals exhibited selective lithium ion diffusion via conduction paths consisting of lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) and small molecules such as ether or amine compounds. In the present review, the correlation between the crystal structure and ion conductivity of the obtained molecular crystals is addressed based on the systematic structural control of the ionic conduction paths through the modification of the component molecules. The relationship between the crystal structure and ion conductivity of the molecular crystals provides a guideline for the development of solid electrolytes based on supramolecular solids exhibiting rapid and selective lithium ion conduction.     

含PVDF-HFP多孔骨架和交联PEG的锂离子凝胶膜制备与性能

锂离子导电膜是锂离子电池的核心材料,研究了以可溶胀聚合物多孔膜作为骨架、在其孔道内填充凝胶结构而制备的锂离子导电膜.首先采用溶液相转化法制备了聚(偏氟乙烯-六氟丙烯)(PVDF-HFP)多孔膜,然后将多孔膜浸入含有锂盐、聚乙二醇二丙烯酸酯(PEGDA)和过氧化苯甲酰的碳酸酯溶液吸收电解液,再加热引发PEGDA中双键交联得到具有多孔骨架和交联PEG的锂离子凝胶聚合物电解质膜(Li-GPEM).失重、力学和及电化学性质分析表明,所制备的Li-GPEM的电导率为2.25mS/cm,综合性能优于PVDF-HFP多孔膜吸附液态锂盐溶液的体系和共混凝胶膜体系.     

Electronic and ionic conduction in some simple lithium salts

The electrical conductivity () and thermoelectric power (S) of solidified melt samples of Li₂MoO₄, Li₂WO₄ and Li₂SO₄ are presented in the temperature range 415 K to melting point of each compound. The ratio of ionic to electronic contribution to has been obtained with the help of a time-dependence study of d.c. electrical conductivity. It has been shown that in Li₂MoO₄ electronic contribution to remains high up to its melting point (about 8% just below the melting point) and it shows no superionic phase. However, in Li₂WO₄ and Li₂SO₄ a superionic phase is obtained in which the ionic contribution to is more than 99.99%. However, in normal ionic (or) phase it is small and decreases with decreasing temperature. Separate temperature variations of ionic ( _i) and electronic ( _e) conductivities are presented and the conduction mechanisms are discussed. It is shown that ionic conduction in the-phase is dominated by Schottky-type defects.     

Properties and structure of germanium-containing lithium aluminoborate glasses

Glasses of the system Li₂O–Al₂O₃–GeO₂–B₂O₃ have been investigated. The effect of replacement of the B₂O₃ by GeO₂ on the physicochemical properties of the glasses has been studied. The density and the refractive index were found to increase as the GeO₂:B₂O₃ ratio (r) increases. In contrast, the molar volume was found to decrease as r increases. Dilatometric measurements showed that the thermal expansion coefficient () increases with the increase of r whereas both of the glass transition temperature (T_g) and the softening point (T_s) decreases with increasing r. Fourier transform infrared (FTIR) spectroscopy revealed that BO₃ structural units increase at the expense of BO₄ units as r increases. It is indicated also that GeO₆ units are the preferred germanium structural units that participate into the glass network. The electrical conductivity was found to decrease with increasing r. This was attributed to the large difference between the two atoms (Ge and B), which increases the stability and therefore decreases the conductivity of the investigated glasses. The conductivity results were correlated with those from the FTIR study.     

Influence of strontium for calcium substitution in bioactive glasses on degradation,ion release and apatite formation

Bioactive glasses are able to bond to bone through the formation of hydroxy-carbonate apatite in body fluids while strontium (Sr)-releasing bioactive glasses are of interest for patients suffering from osteoporosis, as Sr was shown to increase bone formation both in vitro and in vivo. A melt-derived glass series (SiO₂–P₂O₅–CaO–Na₂O) with 0–100% of calcium (Ca) replaced by Sr on a molar base was prepared. pH change, ion release and apatite formation during immersion of glass powder in simulated body fluid and Tris buffer at 37°C over up to 8 h were investigated and showed that substituting Sr for Ca increased glass dissolution and ion release, an effect owing to an expansion of the glass network caused by the larger ionic radius of Sr ions compared with Ca. Sr release increased linearly with Sr substitution, and apatite formation was enhanced significantly in the fully Sr-substituted glass, which allowed for enhanced osteoblast attachment as well as proliferation and control of osteoblast and osteoclast activity as shown previously. Studying the composition–structure–property relationship in bioactive glasses enables us to successfully design next-generation biomaterials that combine the bone regenerative properties of bioactive glasses with the release of therapeutically active Sr ions.     

Direct current electrical conduction in lead tungsten phosphate glasses

Measurements have been made on d.c. electrical conductivity of semiconducting lead tungsten phosphate glasses (X mol% WO₃–(60–x) mol% PbO–40 mol% P₂O₅;x= 10, 20, 30, 40, 50 and 60) of six different compositions over a temperature range of 240 to 500 K. It is shown that the conduction can be described by a small polaron hopping model. When the WO₃ content is 30 mol% the d.c. conductivity _dc decreases and the activation energyW increases with increasing WO₃ content and the glass samples exhibit predominant ionic conduction, however, when the WO₃ content is > 30 mol%, _dc increases andW decreases with the increase of tungsten ion concentration and the glass samples exhibit electronic conduction. The electronic conduction in these glasses havingx > 30 mol% seems to be adiabatic. Greaves variable range hopping has been found to be valid. The value of the electron wavefunction decay constant a is of the order of 16 nm^–1. A minimum in the d.c. conductivity has been observed when the PbO concentration is 30 mol%.     

Glass formation in the system PbO-PbCl2

The preparation of glasses in the system PbO-PbCl₂ is described. The behaviour of the glass transition temperatures, heat capacities and microhardnesses as a function of glass composition has been investigated. The variations are discussed in terms of the structural features of the glasses.Communication No. 256 from the Solid State and Structure Chemistry Unit.