Defect model for the mixed mobile ion effect revisited: An importance of deformation rates

The progress in understanding the behavior of glassy mixed ionic conductors within the concept of the defect model for the mixed mobile ion effect [V. Belostotsky, J. Non-Cryst. Solids 353 (2007) 1078] is reported. It is shown that in a mixed ionic conductor (e.g., mixed alkali glass) containing two or more types of dissimilar mobile ions of unequal size sufficient local strain arising from the size mismatch of a mobile ion entering a foreign site cannot be, in principle, absorbed by the surrounding network-forming matrix without its damage. Primary site rearrangement occurs immediately, on the time scale close to that of the ion migration process, through the formation of intrinsic defects in the nearest glass network. Neither anelastic relaxation below glass transition temperature, T_g, nor viscoelastic or viscous behavior at or above T_g can be expected being observed in this case because the character of the stress relaxation in a wide temperature range is dictated above all by the deformation rates employed locally to the adjacent network-forming matrix. Since the ion migration occurs on the picosecond time scale, the primary rearrangement of the glass network adjacent to an ionic site occurs at rates orders of magnitude higher than those of the critical minimum values, so the matrix demonstrates brittle-elastic response to the arising strain even at temperatures well above T_g, which explains, among other things, why mixed alkali effect is observable in glass melts.     

Defect characterization of mixed SrCa tartrates

A few defect characteristics which are typical of gel-grown mixed single crystals of SrCa tartrates (Sr_1−XCa_xC₄H₄O₆ · 4H₂O) having different concentration, x, of the cations have been described. The temperature of decomposition has been found to be related, to some extent, to dislocation concentration. The magnitude of configurational entropy, which is a manifestation of lattice disorder, has been computed. The Vickers microhardness and dislocation density of crystals have been found to bear good correlation. An empirical formula has been suggested to explain the observed variation in microhardness with the concentration of ions in the mixed lattice.     

Defect studies in CuBIIIC chalcopyrite compounds using the ion channeling technique

Based on simple approximations the backscattering minimum yield is estimated for axial ion channeling in perfect crystals of six CuB^IIIC chalcopyrite compounds. The results obtained for CuInSe₂ are compared with experimental channeling spectra. Point defect concentrations up to about 10²¹ cm⁻³ are estimated for CuInSe₂ single crystals grown by the vertical Bridgman method. A simple power law is found for the fluence dependence of the damage density in oxygen implanted CuInSe₂ single crystals.     

The mixed alkali effect: Theoretical considerations

A cooperative theory for the composition dependence of activated processes in binary ionic oxide glasses (the mixed alkali effect) is proposed. It employs the regular solution model and introduces a molecular model, both of which are used in conjunction with appropriate spectroscopic data for obtaining an estimate of the magnitude of the theory's parameters. The nonlinear composition dependences of certain physical properties of mixed alkali systems, as well as their separation into exponential and pre-exponential factors, are shown to follow from these theoretical considerations.     

The mixed alkali effect in lithium-sodium borate glasses

The electrical conductivity of a series of 0.35 (Li, Na)₂O·B₂O₃ glasses shows a minimum at the composition Na/(Na+Li)～0.6, which becomes stronger as the temperature is decreased; the activation enthalpy for electrical conductivity shows a maximum at this composition. In general, replacing 1% of the total oxygen concentration by chlorine or bromine (keeping the total alkali content fixed) in these glasses increases the conductivity; fluorine doping has an opposite effect. The mixed alkali effect, expressed in terms of the compositional dependence of the activation enthalpy for conductivity, is enhanced when borate glass is doped with fluorine, but is slightly diminished when doped with chlorine or bromine. The results are explained in terms of the structure of halogenated alkali-borate glasses, and discussed in relation to the origin of the mixed alkali effect.     

Influence of space-charge effect on the ion distribution in evaporated SiO dielectrics

Equations are presented to calculate the ionic distribution in a thin film SiO capacitor at dc conditions. The space-charge effect on the potential distribution is taken into account. The theory can then be applied for high ion concentrations. Experimental results obtained with SiO and Al₂O₃SiOAl₂O₃ capacitors show that the space charge may not be neglected.     

The effect of pressure on fast ion conductivity in glasses

We have measured the effect of pressure and temperature on the ionic conductivity of glasses in the system B₂O₃/Li₂O(LiX)₂ (X = F, Cl, Br, I), where X_B2O3 ? 0.7 and X/O ratio was varied while maintaining a constant Li⁺ content of X_(LiX)2 + Li₂O ? 0.3. All glasses exhibited a very small pressure coefficient of conductivity, i.e. ΔV ? 1 cm³ mol^?1, which decreased very slightly as the Cl/O ratio increased or as Cl was replaced by Br at constant X/O ratio. The results were compared with the ELectrostatic Strain Energy theory; the results of this comparison lead to the conclusion that for Li⁺ conduction the electrostatic term is dominant in determining the activation energy for conduction.     

Kinetic anomalies of mixed crystal growth and their effect on the crystal isomorphic composition

Growth rate anomalies in aqueous solution growth of NaClO₃ and KClO₃ were first revealed by V. V. Sipyagin in 1967 and attributed to “kinetic anomalies”. These phenomena were confirmed in a series of other studies and for a variety of substances. Therefore, some universality of these anomalies was supposed that should be due to structural transformations in the liquid solutions. In this paper, we present for the first time results on growth rate oscillations found in mixed crystal growth and their impact on the isomorphic composition of solid solutions. Thick (100) Na(Cl,Br)O₃ layers were grown at fixed supercooling conditions onto NaClO₃ seeds in a microcrystallization cell equipped with an optical microscope. In the temperature range of 33 – 41 °C, four kinetic anomalies were found in solutions of a chlorate: bromate molar ratio of 20: 1 at supercoolings of 2.0 K and 3.0 K. Lattice parameter measurements of the grown Na(Cl,Br)O₃ layers revealed a linear dependence of lattice constant vs. growth rate. By measuring Vegard's law (lattice parameter vs. solid solution composition) we were able to determine the oscillations in mixed crystal composition that accompany the kinetic anomalies in solid solution systems. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The effect of ion exchange on glass surface morphology and composition

The surface morphology and K⁺, Na⁺ concentration distributions of plate glass were investigated by atomic force microscope (AFM) and electron probe microanalyzer (EPMA) before and after ion exchange. The AFM images indicate that the surface microcrack of chemical strengthened glass can be closed to a certain extent and the surface smoothness can be improved. The EPMA results indicate that the relationship between the weight gain and time, temperature follows Fick’s law, which are same as that of the thickness of ion exchanged layer, the total exchanged amount. Consequently, a simple and accurate weighing method was first proposed to estimate the ion exchange state.     

Adhesion property of polyolefin part for mobile device

Abstract

The value of the critical surface tension(γ_c.0) of the polyolefin part calculated by Zismann plot was 26.1?dyne/cm. The surface state and the γ_c,0 of the polyolefin part were changed by solvent treatment. Polyolefin part was influenced by solubility parameter of a solvent, on the other hand the degree of change in the surface state was dependent on a surface tension of a solvent. When a surface tension of solvent is lower than γ_c.0 of the polyolefin part, the wettability of a solvent was good and the surface state was greatly changed. The adhesion strength of polyolefin part was greatly improved to as compared to that of the untreated one. As the γ_c,0 of polyolefin part was closed to the surface tension of the primer, the good adhesion strength was obtained for γ_c/γ_L,p ≤1.     

Oxygen ion concentration in solvents for the growth of garnets

A concentration cell for the determination of the oxygen ion concentration by means of e. m. f. measurements is described which is suitable for oxidic melts with low viscosity and high attack on ceramic materials. Applying this concentration cell binary mixtures of oxides and fluorides used as solvents for the garnet preparation were investigated. The oxygen ion concentration is given in dependence on the composition of the mixtures. By comparison with simple models conclusions on the structure of the melt are made.     

Defect structure and the nature of the obstacles for dislocations in NaCl(Ca) crystals

On the basis of the investigation of the influence of Ca concentration on yield point at different strain rates it is revealed the nature of the obstacles for dislocations overcomed with and without thermal activation.     

The importance of the oxygen ion concentration for oxidic high-temperature solvents

Using e.m.f. measurements we determined relative oxygen ion concentrations of the systems PbO—PbF₂—B₂O₃, PbO—MoO₃—B₂O₃, PbO—Bi₂O₃—V₂O₅, 3 PbO · MoO₃—Fe₂O₃, and 3 PbO · MoO₃—Ga₂O₃. Furthermore the alteration of the relative oxygen ion concentration of pure PbO was observed after stepwise addition of the solvent components PbF₂, B₂O₃ and of the garnet forming oxides Fe₂O₃ and Y₂O₃ giving complete high temperature solutions for the Y₃Fe₅O₁₂ preparation. Applying the Lux' acid-base concept the behaviour of these oxide mixtures is discussed. Combinations which contain weak bases and weak acids allow the adjustment of a desired oxygen ion concentration that is little changed by added oxides for crystal growth. These combinations show favourable properties as solvents for oxidic substances with complicated compositions, e.g. perovskites, garnets, ferrites.     

The effect of fluoride ion concentration on apatite formation and on its crystal habit

The effect of fluoride ions on the rate of apatite [ca_10(PO4)6(F,OH)₂] formation and on its crystal habit was investigated. It was found that both at high and at low fluoride concentrations the rate formations is retarded. At two optimal concentrations, namely at 3.4 and 5.5 fluoride: apatite excess of the stoichiometric ratio, the rate is the highest. The crystal habit of the apatite formed at high fluoride concentrations is hexagonal plate-like, while the apatite formed at low fluoride concentrations is dendritic or needle-like. The concentrations of fluoride in the crystals were determined by specific fluoride electrode technique.     

Defect levels in the band gap of amorphous selenium

Energy locations in the band gap have been determined for the thermally accessible levels of the negative-U defect centers in amorphous selenium. Both the temperature dependence of the steady-state photocurrents, and an analysis of emission currents in the post-transit regime of a time-of-flight transient photoconductivity experiment on the same samples, agree on the presence of defect levels at (0.42 ± 0.04) eV above the valence band mobility edge and (0.53 ± 0.06) eV below the conduction band. Both measured current levels and the resolved energy positions of the defects are subject to the Poole-Frenkel effect.     

The mixed alkali effect in sodium and potassium galliosilicate glasses II. DC electrical conductivity

The DC electrical conductivities of several series of mixed alkali galliosilicate glasses have been measured. The appearance of a minimum in the electrical conductivity of these glasses, independent of the gallium content, suggests that the mixed alkali effect is independent of the non-bridging oxygen content. These results are discussed in terms of current theories proposed to explain this anomalous behaviour.     

Study of ion transport behavior in a mechanochemically synthesized silver halide mixed composite system: [0.75 AgI:0.25 AgCl]

Ion transport behavior in a mechanochemically synthesized silver halide mixed composite has been investigated. AgI and AgCl, in 75: 25 mol. wt. (%) ratio, has been prepared by high energy ball milling for different milling times viz. 5, 10, 20, 30, 40, and 50 h as well as by simple physical mixing (referred to as zero hour milling). The room temperature conductivity has been evaluated as a function of milling time. The conductivity increased initially with increasing milling time, then decreased. The increase in conductivity has been attributed to the increased degree of amorphosity in the sample as a consequence of high energy ball milling. The 30-hour milled sample exhibited highest conductivity with an enhancement of more an order of magnitude from that of zero hour milled sample. To explain the ion transport mechanism in the optimum conducting sample, other basic ionic parameters viz. ionic mobility (μ), mobile ion concentration (n), ionic transference number (t_ion) etc. have also been determined. The materials and structural properties have been characterized using XRD, FTIR, and DSC techniques. Using the optimum conducting sample as electrolyte, all-solid-state battery has been fabricated having cell configuration: Ag (anode) // (0.75 AgI:0.25AgCl) // C + I₂ + Electrolyte (cathode), and the cell performance has been studied under varying load conditions.     

Phosphate glasses for GRIN structures by ion exchange

Phosphate glasses were treated as a material for GRIN-lens production by silver-alkaline ion exchange. Glass durability (in salt melts) known to be a general obstacle for using these glasses in ion exchange technologies was found to profoundly increase in the sequence of meta ? piro ? orthophosphate. It is supposed to be due to the structure of phosphate glasses, which transforms in this sequence from 1D to 3D space arrangement of the glass-forming network. Ion exchange properties of these glasses were studied as well, and the maximal index variation in sodium–silver ion exchange was found to be 0.17.     

CdZnTe晶体的缺陷能级分析

通过测试富Cd原料无籽晶垂直布里奇曼法生长出的高阻Cd0.8Zn0.2Te (CZT)单晶体的I-T特性曲线,利用热激活能原理来分析单晶体内的缺陷,结果得到晶体中有一个由镉空位引起的电子陷阱,其深度为0.539eV.由于俘获能级有较高的激活能,在常温下,价带上的载流子不会被激发,所以该晶体适用于制作室温核辐射探测器.另外还研究了CZT晶体在室温下的I-V特性,测得采用该方法生长的CZT单晶体电阻率高达5.0×1010Ω*cm,制作的核辐射探测器在室温下获得了比较好的241Am 59.5keV能谱.