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991.
Quantum dots (3–4?nm) of Zn1? x Cd x S (both free of Mn2+ and with Mn2+ incorporated) were synthesized through a novel solvothermal-microwave irradiation technique. Detailed structural analysis of the Zn1? x Cd x S and Zn1? x Cd x S:Mn2+ (x?=?0, 0.25, 0.5, 0.75 and 1) materials was carried out using powder X-ray diffraction technique. For all the compositions, the crystallite size was controlled to less than 1.5?nm. The optical energy gap for Zn1? x Cd x S was found to vary from 3.878 to 2.519?eV and for Zn1?x Cd x S:Mn2+ it varies from 3.830 to 2.442?eV when x is increased from 0 to 1. Overall, the optical energy gap could be tuned from a minimum of 2.442?eV to a maximum of 3.878?eV. DC conductivity analysis (from 40°C to 150°C) and electrical energy gap analysis for all the compositions were also performed. The dc conductivity for Zn1? x Cd x S solid solutions varies from 0.3840?×?10?10 to 8.7782?×?10?10?mho/m at 150°C and for Zn1? x Cd x S:Mn2+ it varies from 0.5751?×?10?10 to 9.8078?×?10?10 mho /m at 150°C (for x?=?0 to x?=?1). The method of synthesis and the results observed in this investigation may assist in the fabrication of optical devices when the required operational performance falls under the range observed in the study. 相似文献
992.
The thermal conductivity (κ) of single crystals of tetragonal uniaxial antiferromagnets USb2 (T N = 202 K) and UBi2 (T N = 180.8 K) has been measured along the a-axis (κa ) over the temperature range from 0.5 to 300 K and along the c-axis (κc ) from 0.5 to 70 K. The as-grown samples have residual resistivity ratio (RRR) values of about 500–600 and 100–150 for UBi2 and USb2, respectively. The anisotropy of the thermal conductivity (κa (T)/κc (T) ~ 5) and the low-T Lorenz ratios are discussed in relation to Fermi surface topology for both compounds. 相似文献
993.
994.
Functionalized multiwall carbon nanotubes (MWCNT-COOH) were decorated with crystalline cobalt ferrite nanoparticles (CoFe2O4 NPs) by co-precipitation reaction to form MWCNT-COOH/CoFe2O4 hybrid. The hybrid was characterized by X-ray diffraction analysis, transmission electron microscopy (TEM), Fourier transfom infrared spectroscopy and vibrating sample magnetometry. The results confirmed that MWCNTs and CoFe2O4 NPs coexisted in the hybrid. The TEM results showed a thick layer of CoFe2O4 was intimately connected to the surface of MWCNTs. The saturation magnetization value of the hybrid was 11.5 emu/g. There has been a high frequency fluctuation in conductivity, however, above all dc conductivity changes and resulting activation energy is calculated from the Arrhenius plots. It is found to vary with the temperature regions. This can be attributed to the existence of a conventional temperature independent tunneling conduction mechanism, which can be also explained that the metallic conduction is a dominant mechanism around room temperature. The ac conductivity of MWCNT-COOH/CoFe2O4 hybrid might also be a consequence of the predictions of the universal dynamic response and the ‘n’ power exponents could be determined with lower concentration of the addition in the hybrids. 相似文献
995.
Oxygen ion conductivity of Lao.sSro.2Gao.s3Mgo.17-xCoxO3-δ synthesized by laser rapid solidification 下载免费PDF全文
Materials Lao.8Sro.2Gao.83Mgo.17_xCox03_6 with x = 0, 0.05, 0.085, 0.10, and 0.15 are synthesized by laser rapid solidification. It is shown that the samples prepared by laser rapid solidification give rise to unique spear-like or leaf-like microstructures which are orderly arranged and densely packed. Their electrical properties each show a general depen dence of the Co content and the total conductivities of Lao.8Sro.2Gao.83Mgo.085Coo.08503_6 prepared by laser rapid solidification are measured to be 0.067, 0.124, and 0.202 S.cm-1 at 600, 700, and 800 ℃, respectively, which are much higher than by conventional solid state reactions. Moreover, the electrical conductivities each as a function of the oxy gen partial pressure are also measured. It is shown that the samples with the Co content values 〈 8.5 mol% each exhibit basically ionic conduction while those for Co content values 〉 10 mol % each show ionic mixed electronic conduction under oxygen partial pressures from 10-16 atm (1 atm = 1.01325 x 105 Pa) to 0.98 atm. The improved ionic conductivity of Lao.sSro.2Gao.83Mgo.085Coo.08503 prepared by laser rapid solidification compared with by solid state reactions is attributed to the unique microstructure of the sample generated during laser rapid solidification. 相似文献
996.
Heating of a conductive polydisperse powder by electrostatic discharge (ESD) is modelled numerically. Powder packing is described using a discrete element model; powder resistance is defined by geometry of particle contacts and properties of plasma produced by electrical breakdown between neighbour particles. A set of parametric calculations in combination with experimental data is used to determine necessary adjustable model parameters. The model predicts the temperature for each powder particle resulting from its heating by the ESD current. Location and packing of individual particles within the powder affects greatly their achieved temperatures and thus the likelihood of ignition. Consistently with experiments, a trend showing that smaller particles are generally heated to higher temperatures at a given ESD energy is detected for coarser powders; this trend becomes less clear for finer powders with particle sizes less than the breakdown distance given by the Paschen curve in air. Comparison of the experimental data and calculations suggests that the transition from single particle to cloud combustion occurs when the distance between the particles ignited by ESD becomes close to the flame size for the individual burning particle. This distance, inversely proportional to the number of ignited particles, is primarily determined by the ESD energy. 相似文献
997.
The aim of this paper was to investigate electric field induced effects in mixtures of nematic liquid crystals (NLCs) with positive electric anisotropies (MCL 6601 Merck) with carbon nanotubes (MWCNT from Aldrich). In planar alignment, the current–electric field dependence and the current–temperature dependence were explained by assuming a Poole–Frenkel effect (i.e. a tunnelling mechanism) and good agreement with the experimental data was obtained. Within this high field range it resulted that in planar aligned NLC–CNTs mixture the conductivity decreases when the temperature was increased. In homeotropic aligned mixture, the conduction mechanism is similar to the one occurring in a semiconductor: the conductivity increases when increasing temperature. This happens because in thin liquid crystal cells there is a possibility to realize an inner contact between nanotubes and electrodes so the mixture behaves like a semiconductor. 相似文献
998.
The DC electrical resistivity (p) was studied for Co substituted SbNi ferrites as a function of temperature and composition. The experimental results showed that DC resistivity, Curie temperature and activation energies for electrical conduction increase as Co-ion substitution decreases. The DC electrical conductivity increases as temperature increases. The real part of dielectric constant (e') was found to be inversely proportional to the root mean square value of the electrical resistivity. 相似文献
999.
M. A. El Hiti 《Phase Transitions》2013,86(2):117-122
The DC electrical conductivity was studied as a function of both composition and temperature for the ferrite system NixMg1–xFe2O4 prepared by the usual ceramic technique. The experimental results proved that, the DC electrical conductivity increases as the temperature increases and as the nickel ion content and porosity decrease. The Curie temperature and the activation energies for electrical conduction increase as the nickel ion content increases. 相似文献
1000.
J. Banys J. Macutkevic V. Samulionis A. Brilingas Yu. Vysochanskii 《Phase Transitions》2013,86(4):345-358
Investigation results of dielectric and ultrasonic properties of layered CuInP2S6 crystals are presented. At low frequencies, dielectric spectra are highly influenced by the high ionic conductivity with the activation energy of 7357.4?K (0.635?eV). The high-frequency part of the spectra is determined by relaxational soft mode. The critical slowing down and Debye-type dispersion show the order–disorder type of the phase transition. The temperature dependence of the relaxational soft mode and dielectric contribution show a quasi-one-dimensional behaviour. Ultrasonic velocity exhibits critical slowing down which is accompanied by attenuation peaks in the phase transition region. Layered CuInP2S6 crystals have extremely large elastic nonlinearity in the direction perpendicular to layers. The nonlinear elastic parameters substantially increases at the PT temperature. 相似文献