Phase transition and mixed oxide-proton conductivity in germanium oxy-apatites

La_9.75□_0.25(Ge₆O₂₄)O_2.62 oxy-apatite shows a phase transition from triclinic to hexagonal symmetry at approximately 1020 K that has been characterised by high-temperature synchrotron X-ray and neutron powder diffraction, and ionic conductivity measurements. The crystal structure at 1073 K has been determined from joint Rietveld refinements of synchrotron X-ray and neutron powder diffraction data. The study shows that hexagonal-La_9.75□_0.25(Ge₆O₂₄)O_2.62 contains interstitial oxygen at the position previously reported for other oxy-germanates. Changes in the oxide conductivity associated with this structural transition are discussed. The thermal analyses showed a weight loss on heating close to 600 K very likely due to water release. The synchrotron thermodiffractometric study shows an anomaly in the cell parameters evolution at that temperature, which indicates that this residual water is located into the apatite channels. The electrical characterisation under different atmospheres (dry and wet synthetic air) indicates that there is a significant proton contribution to the overall conductivity below 600 K, mainly under wet atmosphere.     

Aspects of thermal conductivity relative to heat flow

Summary The various techniques and methodologies of thermal conductivity measurement have been conventionally based on the determination of the rate of directional heat flow through a material having a unit temperature differential between its opposing faces. The constancy of this rate depends on the material density, its thermal resistance and the heat flow path itself. The last of these variables contributes most significantly to the true value of steady-state axial and radial heat dissipation depending on the magnitude of transient thermal diffusivity along these directions. The purpose of this paper is to exemplify the above features by defined parameters of heat flow measurement by existing methodologies. No new method is proposed here. Importantly, the relationship between the rate of heat transfer, total heat transferred and thermal conductivity at a given temperature under steady-state conditions for a fixed heat flow path will be illustrated.     

Thermal properties of sodium acetylacetonate

Sodium acetylacetonate was prepared by the interaction of acetyl acetone with sodium hydroxide. The thermal conductivity, phonon velocity, mean free path, Yong's modulus, and the thermal expansion coefficient were studied. The thermal conductivity of the material decreases with increasing temperature due to the thermal lattice scattering of phonons. The velocity of phonons is also decreased due to the perturbation of thermal phonons. The linear thermal expansion coefficient increases with temperature due to the weakness of the attractive forces between the small Na⁺ cations and bulkier acetylacetonate anions in the lattice.

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Zusammenfassung Natriumacetylacetonat wurde durch die Wechselwirkung zwischen Acetylaceton und Natriumhydroxid gewonnen. Es wurde die Wärmeleitfähigkeit, die Phononengeschwindigkeit, die mittlere freie Wegstrecke, das Elastizitätsmodul und der Wärmeausdehnungskoeffizient untersucht. Die Wärmeleitfähigkeit der Substanz nimmt wegen der thermischen Gitterstreuung der Phononen mit steigender Temparatur ab. Die Geschwindigkeit der Phononen nimmt auf Grund der Perturbierung der thermischen Phononen ebenfalls ab. Der lineare Wärmeausdehnungskoeffizient steigt mit zunehmender Temperatur an, was auf die schwachen Anziehungskräfte zwischen den kleinen Na⁺ Ionen und den massigen Acetylacetonat-Anionen im Gitter zurückzuführen ist.

     

Unipolar conductivity of donor or acceptor solutions

Donor or acceptor compounds in apolar organic solvents become charged at a high-field strength electrode and are driven to a surrounding low-field strength electrode of opposite sign. At 10 kV per cm the solutions conduct 3–7 times better when the highly charged electrode is positive in donor solutions. The opposite situation occurs in acceptor solutions.     

Thermal conductivity measurements on ferrofluids

The thermal conductivity of a number of ferrofluids consisting of colloidally dispersed Fe₃O₄ particles in diester, hydrocarbon, water and fluorcarbon carriers have been measured at 38°C. The variation in thermal conductivity with particle concentration is well described by Tareef's equation (1940). This has enabled the ratio of the physical to magnetic size to be determined and compared with estimates of the ratio obtained from electron micrographs and magnetic measurements.The fit between theory and experiment is particularly good for hydrocarbon carrier fluids giving the ratio of solid to magnetic radiusR _i/R _m=1.24±0.03 compared with the value obtained from magnetic data and electron micrographs of 1.19±0.07. The corresponding value from the fluids with a diester carrier ranges between 1.1<R _d/R _m<1.3 which is again consistent with microscopy and magnetic data.The application of a magnetic field of 0.1 T had no noticeable effect on the thermal conductivities of ferrofluids.     

Effect of Oxygen Redistribution on the Normal and Superconducting Properties of Yttrium High‐Temperature Superconductors

An anomaly is found in the vicinity of T_max 560$ K on electric resistance versus temperature curves for yttrium hightemperature superconductors of the 123 phase. Xray phase analysis suggests a structural phase transition in the vicinity of T_max due to oxygen redistribution in the mobile sublattice of this compound. Investigation of samples with Y partially replaced by Ca has shown that the structural phase transition does not depend on carrier concentration in the conduction band.     

由聚苯胺粒子组成的电流变液的研究

由经碱处理的掺杂态聚苯胺（ＰＡｎ）制得高介电常数的半导体ＰＡｎ粒子，将其悬浮于电绝缘油可组成电流变液，讨论了电流变（ＥＲ）液的静态屈服应力（τ＿ｓ），电流密度等性能与ＰＡｎ的介电常数（ε＿ｐ），导电率（σ），体积分数和应用电场强度的关系。对导电率相同的ＰＡｎ粒子，用氨水处理的ＰＡｎ粒子ε＿ｐ较用ＮａＯＨ液处理的高，前者在σ足够低如σ≤１．０×１０￣（－７）／ｃｍ时，ＥＲ液的τ＿ｓ随偶极系数的平方（β￣２）的增大而呈现非线性增加；后者ＥＲ液的τ＿ｓ随β￣２的增大出现一最大值．结果表明：由聚苯胺粒子可组成高电流变活性的无水ＥＲ液．     

Errors involved in the activation energy calculated by integral methods when the frequency factor depends on the temperature ( A = A 0 T m)

The dependence of the frequency factor on the temperature (A=A ₀ T ^m) has been examined and the errors involved in the activation energy calculated from some integral methods without considering such dependence have been estimated. Investigated integral methods are the Coats-Redfern method, the Gorbachev-Lee-Beck method, the Wanjun-Yuwen method and the Junmeng-Fusheng method. The results have shown that the error in the determination of the activation energy calculated ignoring the dependence of the frequency factor on the temperature can be rather large and it is dependent on x=E/RT and the exponent m.     

（H2O）^＋n（n=1,2）的几何结构优化和振动光谱分析

采用Ｈａｒｔｒｅｅ－Ｆｏｃｋ和ＭＰ２方法在多种水平下优化了（Ｈ２Ｏ）＾＋ｎ（ｎ ＝１，２）的几何结构，并进行了振动光谱分析。结果表明：对（Ｈ２Ｏ）＾＋采用ＭＰ２／６－３１１＋＋Ｇ（ｄ，ｐ）可得出最满意的结论。