Electrical properties of exchange-enhanced systems: Fe in (Pd95Rh5)

The electrical resistivity of the giant moment system Pd₉₅Rh₅ containing between 0.8 and 1.85 at % Fe has been measured from 1.4 to 300 K. The incremental resistivity in alloys containing more than 1.25 at % Fe is found to exhibit aT ² limiting low-temperature form; however for the 0.8 and 1.1 at % Fe alloys such aT ² form is not clearly discernible, with (T) exhibiting a temperature dependence intermediate betweenT ² andT ^3/2. The former result is predicted from conduction electron-magnon scattering for which wave vector conservation holds, from which it is inferred that the criterion for wave vector conservation in this type of alloy isnot determined by mean free path effects. Estimates of the acoustic spin-wave stiffnessD are derived from the measuredT ² coefficients. These resistivity data also enable estimates of the exchange coupling parameterJ _s-local to be made. The magnetic ordering temperatureT _c is considerably less discernible than in single-component hosts but approximate values have been derived for the various alloys, from which estimates of the exchange coupling parameterJ _d-local have been made. In the disordered phase the measured incremental resistivity is found to contain a term which decreases approximately linearly with increasing temperature, at a rate of –(1.1±0.45)10^–3 µ cm/K at % Fe. Using existing pressure data on both Pd- and PdRh-based alloys, it is shown that both the sign and magnitude of this term can be accounted for in terms of the volume dependence of the potential and exchange terms, in conjunction with a large coefficient of thermal expansion.This work has been supported in part by the Defence Research Board under Grant No. 9510-100.     

Electrical properties of non-stoichiometric PZT 95/5 ferroelectric ceramics

Pb_0.99(Zr_0.95Ti_0.05)_0.98Nb_0.02O₃ (denoted as PZT 95/5) ceramics were prepared according to the nominal composition of Pb_0.99+x (Zr_0.95Ti_0.05)_0.98Nb_0.02O_3+x (?0.01 ≤ x ≤ 0.04). The electrical properties as a function of lead oxide (Pb) stoichiometry were evaluated. X-ray diffraction analysis shows that all the as-synthesized PZT 95/5 powders are pure perovskite phase and the unit cell volume increases with the addition of Pb. SEM micrographs indicate the fracture mode tends to be predominately intergranular and grain size gets bigger with the increase of Pb content. The coercive field decreases with the increase of Pb till x = 0.02 and then increases when the excess Pb is over x = 0.02. The remnant polarization first increases and then decreases with the increasing amount of excess Pb. Sample with excess Pb x = 0.03 has the biggest value of remnant polarization.     

Pd/GaN(0001) interface properties

This report concerns the properties of an interface formed between Pd films deposited onto the surface of (0001)-oriented n-type GaN at room temperature (RT) under ultrahigh vacuum. The surface of clean substrate and the stages of Pd-film growth were characterized in situ by X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), ultraviolet photoelectron spectroscopy (UPS), and low energy electron diffraction (LEED). As-deposited Pd films are grainy, cover the substrate surface uniformly and reproduce its topography. Electron affinity of the clean n-GaN surface amounts to 3.1 eV. The work function of the Pd-film is equal to 5.3 eV. No chemical interaction has been found at the Pd/GaN interface formed at RT. The Schottky barrier height of the Pd/GaN contact is equal to 1.60 eV.     

Superconducting and magnetic properties of ternary silicides in some rare earth-noble metal (Rh or Ir)-silicon systems

New families of ternary silicides have been prepared in the RE - Rh or Ir -Si systems and the crystal structures have been determined: RERh₃Si₂, RE₂Rh₃Si₅, RE₂RhSi₃ (RE = Y, La → Er), RERhSi (Y, La, Gd → Er), REIrSi (RE = La, Ce, Nd), RERhSi₂ and REIrSi₂ (RE = La → Gd). The RE₂RhSi₃ compounds crystallize with a new structural type, the other ones are isostructural with already known silicides or borides. Some of the silicides studied whose rare earths are diamagnetic (Y, La) show superconducting transitions above 1.6 K. They have been compared with other superconducting ternary borides, silicides, germanides and phosphides containing rare earths and noble metals. Except the phases with Y and La which are diamagnetic or show Pauli paramagnetism, the other materials order magnetically at low temperature. The onset of magnetic transitions vs. field has been observed for some compounds below 20 kOe at 4.2 K.     

Electrical properties of poly(n-butylamino) (di-allylamino) phosphazene

A new organic–inorganic hybrid polymer, poly(n-butylamino) (di-allylamino) phosphazene, is synthesized and electrical properties of the polymer are reported. From the results of Fourier transform infrared (FTIR), 1H-nuclear magnetic resonance (NMR) and 31P-NMR measurements, it was confirmed that the synthesized polymer was poly(n-butylamino) (di-allylamino) phosphazene. From an Arrhenius plot of d.c. conduction it was found that experimental points fit to two straight lines, that the discontinuous point could be the glass transition (Tg=268.9 K) and that the activation energies are 0.74 and 1.5 eV at temperatures higher and lower than Tg, respectively. Dielectric constant and dielectric loss factors were measured over the temperature range from –20°C to 70°C with frequency 100 Hz100 kHz, and a dielectric loss contour was obtained. A relaxation process with the activation energy of 1.44 eV was found from the dielectric loss contour, which can be attributed to relaxation. A comparison was made between the present results and those of other phosphazene polymers. Because the polymer was non-flammable and shows high resistance and low dielectric constant, it could be used as an insulator in the field of electronics. © 1998 Kluwer Academic Publishers     

Electrical properties of iron (III) molybdate

Electrical transport properties, i.e. a.c. and d.c. electrical conductivities, thermoelectric power and dielectric constant, of Fe₂(MoO₄)₃ have been measured in the temperature range 300 to 1000 K on pressed pellets of a polycrystalline sample, using the two electrode method. Iron (III) molybdate has been found to be a p-type semiconductor with an energy gap of 3.1 eV. Intrinsic conduction occurs at 750 K and the activation energies below and above 750 K are 0.51 and 1.55 eV, respectively. The thermoelectric power increases up to 750 K and after that it decreases with increasing temperature. The dielectric constant increases with temperature over the entire temperature range measured except 650 to 750 K, where it has a constant value.[/p]     

Electrical transport properties of iron (II) molybdate

Electrical conductivity, thermoelectric power and static dielectric constant of iron (II) molybdate have been measured in the temperature range 300 to 1000 K on pressed pellets of polycrystalline sample. It has been found that FeMoO₄ is a p-type semiconductor with energy gap 4.1 eV. Different conduction mechanisms have been found below and above 700 K. Below 700 K conduction is due to a small polaron hopping mechanism and above 700 K conduction is due to large polarons as well as normal band conduction mechanism. Activation energy W, ₀ (T) and charge carrier mobility have been estimated in the two temperature ranges 300 to 700 K and 700 to 1000 K. Dielectric constant increases slowly with temperature up to 700 K and above 700 K, it increases exponentially with temperature.     

PZT 95/5-2Nb铁电陶瓷脉冲换能电输出

讨论了PZT 95/5-2Nb铁电陶瓷在冲击波压缩下的释放电性能,并利用PZT 95/5-2Nb铁电陶瓷设计了三种脉冲电源,分别实现了恒定电流、台阶电流和恒定电压等不同条件的电能输出.实验结果表明,PZT 95/5-2Nb铁电陶瓷可适用于多种性能的脉冲能源,具有电流输出幅值和波形易于控制,电流脉冲上升前沿陡,电源体积小等特点,具有广阔的应用前景.     

Features of the magnetic properties of Co/Si/Co thin-film systems

The magnetic properties of Co/Si/Co thin-film structures grown by magnetron sputtering have been studied using magnetooptical techniques. It is established that the saturation field (H _S) of trilayers exhibits oscillations as a function of the thickness of the semiconductor (silicon) interlayer. This behavior is explained by structural features of the Co/Si/Co system and the presence of antiferromagnetic exchange coupling between magnetic layers via the silicon interlayer.     

Electrical properties of electroplated Cu(Ag) thin films

To increase the electromigration resistance of copper interconnects copper alloy systems are of interest. In the present paper electrical properties of Cu(Ag) films will be discussed with respect to heat treatment and in comparison to copper and other alloy systems. The investigations show that the electrical resistivity of Cu(Ag) films is very low in comparison to other copper alloy systems. Up to an alloy content of about 2 at.% Ag the International Technology Roadmap for Semiconductors criterion of 2.2 μΩcm (scattering by geometrical constraints neglected) can be fulfilled after heat treatment. The various components of the electrical resistivity will be discussed in detail. The investigations show that grain growth and the redistribution of silver and impurities dominate the electrical resistivity evolution.     

Electrical properties of electrodeposited zinc selenide (ZnSe) nanowires

In this work, zinc selenide (ZnSe) nanowires were fabricated on indium-tin oxide coated glass substrate via template-assisted electrodeposition method from an electrolytic solution of zinc (II) sulphate (ZnSO₄·7H₂O) and selenium dioxide (SeO₂). ZnSe nanowires of diameter 100 nm have been fabricated using polycarbonate track-etch membrane. Electrodeposition was done at 30 °C temperature and the length of the nanowires was controlled by adjusting the deposition time. Both morphological and electrical characteristics were studied. Sample characterization was done using scanning electron microscope and X-ray diffraction. I–V measurements reveal that the ZnSe nanowires have non-linear behavior like Schottky diode characteristics. Further, the ZnSe nanowires were used in astable multivibrator which acts as capacitor to give conventional output behavior. The temperature dependent capacitive properties of ZnSe nanowires reveal that ZnSe nanowire can be used as temperature sensor.     

Mg95Ni5-30wt%La0.7Mg0.3Ni2.8Co0.5复合物的吸放氢性能研究

先采用氢化燃烧合成法制备Mg95Ni5,然后将氢化燃烧合成产物与30%(质量分数)La0.7Mg0.3Ni2.8Co0.5合金进行机械球磨复合,球磨时间分别为5、10、15和20h;将Mg95Ni5的氢化燃烧合成产物直接球磨10h用于对比研究.采用X射线衍射仪、扫描电镜、能谱仪及气体反应控制器研究了材料的相组成、微观形貌、颗粒化学成分以及吸放氢性能.研究表明,球磨10h的Mg95Ni5/La0.7Mg0.3Ni2.8Co0.5复合物具有最佳的吸放氢性能,在373K,50s内基本达到饱和吸氢量3.78%(质量分数);在523K,1800s内放氢量为3.83%(质量分数);其起始放氢温度为425K,与Mg95Ni5相比降低了35K,吸放氢性能的改善与复合物的组织结构密切相关.此外,La0.7Mg0.36Ni2.8Co0.5的加入改善了复合物的放氢动力学性能.     

Co(Pd)CuZnLa/硅藻土催化剂改性共沉淀法制备与表征

添加阳离子表面活性剂CTAB,利用共沉淀法制备了硅藻土负载Co-Cu-Zn-La和Pd-Cu-Zn-La的复合金属催化剂,利用SEM、TEM、XRD、FT-IR、TPR等技术对催化剂的表面形貌、结构及还原性能进行了表征。结果表明,制备的催化剂有丰富孔结构,4～15nm的活性氧化物组分呈200～400nm花状分布,分散良好;制备催化剂经H2程序升温还原后,除有金属单质存在外,可能还有合金生成。     

Electrical conductivity and Seebeck coefficient of (La,Ca) (Cr,Co)O3

Electrical conductivity and Seebeck coefficients of (La, Ca) (Cr, Co)O₃ were measured as a function of temperature. The electrical conductivity as measured in air from 100 to 1100 °C increased with increasing Co and Ca content. The Seebeck coefficients were positive, indicating p-type conductivity. The substitution of Co for Cr significantly decreased the Seebeck coefficients, indicating that the substitution resulted in an increase in site occupancy, associated with the Co. The additional Ca substitution for La resulted in further decrease in the Seebeck coefficients, then exhibited a temperature-independent behaviour, indicating that the carrier mobility, rather than carrier concentration, was thermally activated. The activation energies were 0.18 and 0.25 eV for LaCrO₃ and LaCoO₃, respectively, and increased to about 0.50 eV with substitution of 10 mol% Co for Cr and then linearly decreased as Co content increased.     

Carbon nanotube formation over laser ablated M and M/Pd (M = Fe,Co, Ni) catalysts: The effect of Pd addition

Monometallic and bimetallic M and M/Pd (M = Fe, Co, Ni) nanoparticles were prepared by pulsed Nd:YAG laser ablation of bulk M and Pd targets in acetone and transferred onto Si wafers to catalyze carbon nanotubes from decomposition of liquid petroleum gas via thermal chemical vapor deposition at 750°C. Transmission electron microscopy and optical extinction study revealed that the prepared M and M/Pd nanoparticles have rather spherical shape and their aspect ratios are nearly one. In comparison to monometallic M catalysts by addition of Pd, the average sizes of produced bimetallic M/Pd catalysts increased. Carbon nanotubes' characterization revealed that by addition of Pd to laser ablated M catalysts the average diameter, the yield, and quality of end product carbon nanotubes were increased. The average diameter of grown carbon nanotubes increases as: Ni < Ni/Pd < Co < Co/Pd < Fe < Fe/Pd and the quality of them increases as: Ni < Co < Fe < Ni/Pd < Fe/Pd < Co/Pd.