Transport properties of ZnO substituted lead vanadate glass system at eutectic composition

Glasses of the system x(ZnO)(50 − x)PbO:50V₂O₅ were prepared by melt-quench process in the range x = 0–15 mol%. Measurements are reported for dc electrical conductivity as well as thermoelectrical power for the above compositions in the temperature range 27–227 °C. The experimental results are analyzed with reference to various theoretical models proposed for dc electrical conduction in amorphous semi-conductors. The analysis shows that at high-temperatures the temperature dependence of dc conductivity is consistent with Mott's model of phonon-assisted hopping conduction, variable range hopping mechanism and Schnakenberg's model mechanism. The high-temperature thermoelectric power (TEP) was satisfactorily explained by Heikes’ relation and the data also showed evidence of small polaron formation in these glasses. Thermo EMF measurements indicate that all the glass samples including unsubstituted lead metavanadate are n-type at room temperature. As temperature is increased ZnO substituted samples change from n-type to p-type. When Heikes’ formula is applied to all the systems at room temperature the amount of disorder was found to be the same in all the systems. When Emin's formula is used for the estimation of W_D, the activation energy due to disorder, in ZnO substituted samples, unusually large values of W_D (∼0.6 eV) are obtained. The present results indicate that the Emin's formula cannot be directly used to estimate the disorder energy in ZnO substituted lead vanadates. The temperature dependent change of sign of the thermoelectric power S, in these systems may arise due to change in V⁴⁺/V⁵⁺ ratio with the change of temperature or due to the onset of band type of conduction as in MnO or other extrinsic compensated semi-conductors.     

Magnetic properties of Cu substituted Co-ferrite

Copper substituted Co-Cu ferrites Co_1 − xCu_xFe₂O₄ (0 ≤ x≤0.5) have been studied with Mössbauer spectroscopy, x-ray diffraction, and vibrating sample magnetometer (VSM). The Co-Cu ferrite toroidal core samples were sintered at 860-940 °C for 2 h and the initial permeability, quality factor, density and shrinkage were also measured. The crystal structure was found to be an inverse cubic spinel with the lattice constant a₀ = 8.390 Å and a₀ = 8.386 Å for Co-ferrite and Cu²⁺ substituted Co-ferrite, respectively, by Rietveld profile analysis using the FULLPROF program. Hyperfine field was decreased with increasing Cu²⁺ concentration. The saturation magnetization (Ms) of the Co-Cu ferrite annealed at 900 °C decreased drastically and the coercivity, Hc, dropped dramatically from about 1419 to 455 Oe as copper concentration x decreased from 0.0 to 0.5. This shows that Ms, Hc can be controlled using Cu content, and initial permeability and quality factor Q is nearly constant in Cu²⁺ substituted Co-ferrite. The toroidal core data showed that the density and shrinkage of Co_1 − xCu_xFe₂O₄ (0≤x ≤ 0.5) ferrites increased with increasing quantity of Cu ions.     

三价钐离子掺杂钛酸钙发光性能研究

通过溶胶-凝胶法,制备了钙钛矿型CaTiO3∶Sm3+纳米发光材料。采用XRD对样品进行物相表征。通过电致发光和光致发光测试研究了样品中Sm3+的发光特性,Sm3+可发出明亮的橙红色光,但样品的EL和PL谱存在一定的差别。通过分析发光测试结果,认为纳米颗粒中存在两种晶体结构SiteⅠ和SiteⅡ,分析了不同结构对电致发光和光致发光的影响,EL主要依赖于SiteⅠ中Sm3+,PL主要依赖于SiteⅡ中Sm3+,并通过实验验证了基质结构对Sm3+发光的影响。     

Transport properties of antiferromagnetic superconductors

Transport properties of antiferromagnetic superconductors with T _N<T _chave been investigated. Detailed numerical results are given for SmRh₄B₄ by using the following model. The paramagnetic phase (T _NT _c)is described by using Abrikosov-Gorkov theory of magnetic ions in an ordinary superconductor. In the AF phase (TT _N)the effects of the molecular field H _Q (T) and the elastic scattering of conduction electrons from spin fluctuations are included. Expressions for H _Q (T) and the scattering rate from spin fluctuations have been derived. The aim has been to see if properties are enhanced or depressed by the AF ordering occurring below T _N.It is found that whereas the electronic thermal conductivity K _s,nuclear spin relaxation rate R _s,and the longitudinal ultrasonic attenuation _s,are depressed by the AF ordering, the inverse of the magnetic penetration depth, [(T)]^–1 is enhanced below T _N.The effect of all types of impurities is included in the study. Theoretical results for K _sand [(T)]^–1 agree with the experimental values for SmRh₄B₄ (experimental data for other properties are not available in literature). In the above, T _Nis the Néel temperature and T _cis superconducting transition temperature.     

Transport properties of alumina nanofluids

Recent studies have showed that nanofluids have significantly greater thermal conductivity compared to their base fluids. Large surface area to volume ratio and certain effects of Brownian motion of nanoparticles are believed to be the main factors for the significant increase in the thermal conductivity of nanofluids. In this paper all three transport properties, namely thermal conductivity, electrical conductivity and viscosity, were studied for alumina nanofluid (aluminum oxide nanoparticles in water). Experiments were performed both as a function of volumetric concentration (3-8%) and temperature (2-50?°C). Alumina nanoparticles with a mean diameter of 36?nm were dispersed in water. The effect of particle size was not studied. The transient hot wire method as described by Nagaska and Nagashima for electrically conducting fluids was used to test the thermal conductivity. In this work, an insulated platinum wire of 0.003?inch diameter was used. Initial calibration was performed using de-ionized water and the resulting data was within 2.5% of standard thermal conductivity values for water. The thermal conductivity of alumina nanofluid increased with both increase in temperature and concentration. A maximum thermal conductivity of 0.7351?W?m(-1)?K(-1) was recorded for an 8.47% volume concentration of alumina nanoparticles at 46.6?°C. The effective thermal conductivity at this concentration and temperature was observed to be 1.1501, which translates to an increase in thermal conductivity by 22% when compared to water at room temperature. Alumina being a good conductor of electricity, alumina nanofluid displays an increasing trend in electrical conductivity as volumetric concentration increases. A microprocessor-based conductivity/TDS meter was used to perform the electrical conductivity experiments. After carefully calibrating the conductivity meter's glass probe with platinum tip, using a standard potassium chloride solution, readings were taken at various volumetric concentrations. A 3457.1% increase in the electrical conductivity was measured for a small 1.44% volumetric concentration of alumina nanoparticles in water. The highest value of electrical conductivity, 314?μS?cm(-1), was recorded for a volumetric concentration of 8.47%. In the determination of the kinematic viscosity of alumina nanofluid, a standard kinematic viscometer with constant temperature bath was used. Calibrated capillary viscometers were used to measure flow under gravity at precisely controlled temperatures. The capillary viscometers were calibrated with de-ionized water at different temperatures, and the resulting kinematic viscosity values were found to be within 3% of the standard published values. An increase of 35.5% in the kinematic viscosity was observed for an 8.47% volumetric concentration of alumina nanoparticles in water. The maximum kinematic viscosity of alumina nanofluid, 2.901?42?mm(2)?s(-1), was obtained at 0?°C for an 8.47% volumetric concentration of alumina nanoparticles. The experimental results of the present work will help researchers arrive at better theoretical models.     

Mn掺杂快淬NdFeB永磁体磁性能研究

在前期研究工作的基础上,从热磁重(TMA)测量出发对快淬Nd9Fe85-xMnxB6(x=0～2)的相关磁性能及交换耦合效应作了进一步的研究.发现在最佳的热处理条件下,一定的Mn掺杂能提高快淬NdFeB的磁性能,特别是矫顽力最大能提高20%左右,但是更高的Mn掺杂量会导致矫顽力和最大磁能积的明显下降.XRD显示快淬态的NdFeB样品的晶化程度随Mn掺杂量提高而提高,但在最佳的热处理条件下所有的快淬NdFeB样品都包括硬磁性相Nd2Fe14B和软磁性相α-Fe.热磁重(TMA)测量显示一直随着Mn掺杂量提高到2%(原子分数),硬磁性相Nd2Fe14B的居里温度(Tc)在不断下降,但是α-Fe的Tc却随Mn掺杂量提高而提高.认为磁性能和居里温度改变是因为形成了δ-Mn和R2Fe23B3相.当Mn掺杂量较低时高温下有δ-Mn形成并和α-Fe产生交换耦合作用导致α-Fe的居里温度升高,而当Mn掺杂量提高到2at%时形成的R2Fe23B3相固溶δ-Mn相才导致α-Fe的居里温度下降.     

Transport properties of overdoped Tl cuprates

To explain the observed inconsistency between the negative thermopowerS and the positive Hall coefficientR _H in the overdoped Tl cuprates, tight binding calculations are performed which include both Cu-O and O-O interactions in the CuO₂ square lattice. A striking feature of the CuO₂ antibonding band is that a holelike Fermi surface is formed even when the band is less than half-filled. This brings about an unusual electron state in which the Hall (cyclotron) mass along the Fermi surface is holelike but the transport mass perpendicular to it is electronlike. This electronlike transport mass contributes to the negative thermopower.We thank N. Hamada, T. Manako, and T. Kondo for helpful discussions.     

Transport properties of critical dilute solutions

On the basis of the isomorphism of critical phenomena, the behavior of transport properties of binary mixtures in the vicinity of the vapor-liquid critical line is considered. In particular, the renormalization of the singularity of the thermal conductivity in dilute critical solutions has been analyzed in detail. It is shown that the behavior of the thermal conductivity is determined by the critical background, i.e., the fluctuation-induced regular part, which diverges at the critical point of a solvent.     

Transport properties of thin metal films

The electrical conductivity, thermal conductivity and thermoelectric power of a metal film subjected to the simultaneous action of an electric field and a temperature gradient were calculated. Analytical equations for the electrical and thermal current densities in thin metal films were obtained.     

中氮茚接枝的新型聚硅烷的合成及其荧光性能研究

首次报道中氮茚接枝的二甲基二苯基聚硅烷PMPSi-c的合成及其荧光性能研究.结果表明经过中氮茚接枝,聚硅烷荧光强度明显增强,且能发射强烈的蓝色荧光,有望用作蓝光区的荧光材料.     

Effect of trivalent cation on the physicochemical properties of cobalt containing anionic clays

A series of cobalt containing hydrotalcites having the general formula CoMCO3-HT where M = Al, Fe and Cr were synthesized by sequential and coprecipitation methods. The samples were primarily characterized by X-ray diffraction (XRD), infrared absorption studies, transmission electron microscopy-energy dispersive X-ray analysis (TEM-EDAX), thermogravimetry-differential scanning calorimetry (TG-DSC) and BET surface area measurements. The lattice parameters, FTIR stretching wavelengths for O–H bonds and thermal stability depended on the ionic radius of the trivalent M cation. Thermal calcination of these materials yielded a non-stoichiometric spinel-type phase whose crystallinity was also affected by the nature of the trivalent cation. This revised version was published online in November 2006 with corrections to the Cover Date.     

Synthesis,characterization and optical properties of bismuth germanate doped with trivalent europium

Bismuth germanate single crystals doped with trivalent europium were grown by the Czochralski method. Procedures and results of synthesis experiments are reported. Microprobe analysis reveals the segregation of doped rare-earth elements. Spectroscopic studies of Eu³⁺ ions suggests C_3v point symmetry for the cationic site. Oscillator strengths and τ_λ parameters for Eu³⁺ were calculated.     

Transport properties of local spin fluctuation systems

The dynamical susceptibility due to local spin fluctuations in transition metals has been calculated in RPA, employing a generalized Wolff model with different Coulomb interactions at host and impurity sites, modified hopping from or into the impurity sites, and including potential scattering. The electrical and thermal resistivities and the diffusion part of the thermopower have been calculated, assuming well-localized spin fluctuations. The results for resistivity and thermopower turn out to be surprisingly similar to those obtained for Kondo systems. In particular, a giant peak in the thermopower is found which is of the same magnitude and of similar shape in both systems. The deviations from the Wiedmann-Franz law are also strongly temperature dependent, with a maximum of about 16% near the spin fluctuation temperature.     

Transport properties of Cu5SmSe4

The electrical conductivity, Hall coefficient, thermoelectric power, and thermal conductivity of Cu₅SmSe₄ have been measured at temperatures from 80 to 400 K, and its linear thermal expansion coefficient has been determined from X-ray diffraction data. The observed negative a-axis linear thermal expansion coefficient and anomalies in temperature-dependent transport properties of this compound are tentatively attributed to a transition of the samarium atoms from a divalent to a trivalent state.     

Transport properties of coupled semiconductor quantum dots

We have measured the electronic transport properties of the coupled quantum dot devices at low temperatures. The interplay between the strong many body spin interaction and the molecular states are probed in linear and non-linear transport regime. We observe the formation of strong coherent molecular states clearly visible in the double dot conductance phase diagram. In our study, the spin configuration in multiply coupled quantum dots could be identified using Kondo phenomenon. In addition, the characteristics of the spin dependent molecular states and phase dependant tunneling have been also observed using non-linear conductance measurement of the double dots. The results suggest the importance of the diverse spin related physical issues in artificial quantum dot devices.     

Dielectric properties of lanthanum substituted barium titanate microwave ceramics

In this study, we report the high dielectric constant lanthanum substituted barium titanate ceramic material for its possible applications at microwave frequencies. The microwave dielectric characterization of Ba_6 − 3xLa_8 + 2xTi₁₈O₅₄ solid solutions with 0.0 ≤ x ≤ 0.7 prepared by conventional mixed oxide route method has been carried out. The lattice parameters were obtained from the X-ray diffraction patterns. It was observed that lattice parameters increased with respect to an increase in the ‘La’ content. The crystal symmetry investigated was orthorhombic with space group of Pbam. From the evaluation of microwave dielectric properties of lanthanum doped barium titanate ceramics, it was observed that a maximum value of dielectric constant (ε′) = 157 and a minimum tangent loss (tanδ) = 0.0572 was obtained. The minimum value of a.c. conductivity (σ_a.c.) was observed to be 1.76e − 07 S/m.     

Transport properties of fluids near critical points

The paper reviews the theoretical and experimental results for the asymptotic behavior of the dynamics of critical fluctuations in fluids and fluid mixtures near a critical point. The implications of these results for the development of accurate representative equations for the viscosity and thermal conductivity of gases in the critical region are discussed.Invited lecture presented at the 10th International Conference on the Properties of Steam, Moscow, USSR, September 2–7, 1984.