Ionic transport studies of the glassy silver vanadomolybdate system

Ionic conductivity of the Ag₂O-MoO₃-V₂0₅ system has been studied over a wide range of frequency, temperature and composition. A narrower glass forming region has been found in comparison to the corresponding Ag₂O-MoO₃-P₂O₅ and Ag₂O-B₂O₃-P₂O₅ systems. The highest conductivity at room temperature, _rt, = 3.21 × 10^–6–1 cm^–1 (d.c.) with an activation energy,E _act, of 0.466 eV, was observed for the glass former's ratio of unity. Further, it reached a maximum value of 2.2 × 10^–2¨-1 cm^–1 withE _act = 0.153 eV when the oxide-base glass was dissolved with Agl. D.c. conductivity, hopping rate and relaxation time in the present system have been found to be characterized by the same activation energy.     

晶体结构对化合物电学性质的影响

化合物的导电性包括电子(空穴)导电及离子导电两大部分.新材料的发展已将化合物的电学性质提到了急需研究的位置.随着对化合物电学性质研究的不断深入,发现了许多新现象,新性质和新材料,如氧化物高温超导体,稀土半导体,稀土巨磁阻材料等.这些都是电子(空穴)导电的实际应用.而由于新能源探索需适应保护环境的需要,传统的氧离子和质子导体成了人们的首选研究对象,以开发它们在燃料电池、氧分离膜,催化等方面的实际应用.由于不等价置换,价态变化及氧离子具有大的双电荷与阳离子基体的强相互作用及高迁移率,使得大多数的研究工作集中于化合物的结构畸变分析及精化,试图发现新的结构相或者新的电学材料.     

Structure and ionic transport studies of sodium borophosphate glassy system

Sodium borophosphate glasses of composition (mol%) 50Na₂O–50[xB₂O₃–(1−x)P₂O₅], 0 ≤ x ≤ 0.8 have been prepared by melt quenching method and characterized through XRD, DSC, FTIR and impedance spectroscopy techniques. The glass transition temperature increases with the substitution of B₂O₃ due to the cross-linking of the network and the FTIR study shows the presence of different structural units in the network. The ionic conductivity study as a function of composition of B₂O₃ shows increment in conductivity with two conductivity maxima at 10 and 30 mol% of B₂O₃ and conductivity variations with temperature follow an Arrhenius type behaviour. Transport numbers evaluated for ions and electrons show that Na⁺ ions are the mobile species in the investigated systems. The frequency dependence of the electric conductivity follows a simple power law feature. The analysis of various electrical parameters as a function of temperature in different complex planes shows that the charge transport occurs by the hopping mechanism.     

On the electrical transport in nickel telluride

Journal of Materials Science Letters -     

Influence of particle size on electrical transport properties of La0.67Sr0.33MnO3 manganite system

A systematic investigation of lanthanum-based manganite, La0.67Sr0.33MnO3, has been undertaken with a view to understand the influence of varying particle sizes on electrical transport properties. With a view to obtain materials with varying particle size, they were prepared by sol-gel route, sintering at four different temperatures. The samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD data has been analyzed by Rietveld refinement technique and it has been confirmed that the materials have rhombohedral crystal structure with R3c space group. Metal-insulator transition temperatures (Tp) were found to decrease continuously with decreasing particle size where as ferro to paramagnetic transition temperatures (Tc) are found to remain constant. The magnetoresistance (MR) values are found to increase with decreasing particle size. With a view to understand the conduction mechanism, the electrical resistivity data have been analyzed both in the ferromagnetic metallic (T < Tp) as well as high temperature paramagnetic insulating (T > Tp) regions.     

Microstructural and electrical studies on diamond films

X-ray diffraction, atomic force microscopy and electrical studies were performed on 2-3 μm thick diamond films on silicon substrates. The films were produced by the microwave plasma chemical vapour deposition method. The films were polycrystalline having a grain size of 32.1 nm. From room temperature current-voltage measurements, it was found that the charge transport mechanism was due to the thermionic emission over the potential barrier of 1.3 eV.     

The electrical conductivity of some azine compounds

Correlation of the molecular structure and thermal study of the electrical conductivity of benzaldazine (BA) and its NO₂-derivatives were carried out. The values of the activation energies, obtained from the electrical conductivity measurements, as well as the energy gaps calculated from ultra violet (u.v.) and visible spectra obtained either in liquid or in solid forms indicate that all compounds behave like a semiconducting material. Both n*s and *s were found to be the main sources participatiog in the cooduction processes.     

Composition effect on the catalytic activity and electrical conductivity of cobalt oxide compounds

This work examines the catalytic activity and electrical conductivity of electrodeposited nonstoichiometric cobalt oxide compounds. Their composition is Co, 47–53; H₂O, 10–18; and OH⁻ groups, 8–12%. The content of OH⁻ groups is shown to determine their catalytic activity and ionic conductivity. These compounds are potential electrode materials for the reduction of oxygen.     

Ultrasonic studies of the heavy fermion compounds

A review of ultrasonic measurements on the three heavy fermion compounds UPt ₃ , URu ₂ Si ₂ and CeCu ₆ is given. These compounds show one or more of the three types of co-operative behavior; Kondo-like effect, antiferromagnetism and superconductivity; all these features are observed as ultrasonic anomalies. Both UPt ₃ and CeCu ₆ show a strong coherence effect which is akin to a Kondo-like transition in the electronic system. Velocity anomalies are found at the antiferromagnetic transition for URu ₂ Si ₂ . UPt ₃ also has an antiferromagnetic transition which is believed to influence the subsequent superconducting ordering. For UPt ₃ , the superconductivity is of an unconventional nature; multiple superconducting phases have been observed and a complete phase diagram has been obtained from high resolution velocity measurements.     

General theories for the electrical transport properties of carbon nanotubes

We have shown that the general theories of metals and semiconductors can be employed to understand the diameter and voltage dependency of current through metallic and semiconducting carbon nanotubes, respectively. The current through a semiconducting multiwalled carbon nanotube (MWCNT) is associated with the energy gap that is different for different shells. The contribution of the outermost shell is larger as compared to the inner shells. The general theories can also explain the diameter dependency of maximum current through nanotubes. We have also compared the current carrying ability of a MWCNT and an array of the same diameter of single wall carbon nanotubes (SWCNTs) and found that MWCNTs are better suited and deserve further investigation for possible applications as interconnects.     

Electrical transport studies on heavy rare-earth tungstates

This paper reports the measurement of thermoelectric-power (S) at different temperatures (800–1100 K) and electrical conductivity (σ) as a function of electric field strength, time, ac signal frequency and temperature (650–1200 K) for pressed pellets of heavy rare-earth tungstates (HRET) with a general formula RE₂(WO₄)₃ [where RE = Tb, Dy, Ho, Er, Tm and Yb]. These tungstates are typical insulating compounds with room-temperature σ value less than 10^?10 ohm^?1 cm^?1 and become semiconductors at elevated temperature with σ values of the order of 10^?5 ohm^?1 cm^?1 at 1200 K. The S vs T^?1 and log σ vs T^?1 plots are linear, but a change in the slope of straight lines occurs at a temperature (T_B) which lies between 900–1025 K for different tungstates. These break temperatures are the same for both S and σ plots. It has been found that HRET are mixed ionic-electronic conductors. Above T_B the electronic conduction dominates over the ionic conduction, but below T_B both become comparable. The electronic conduction above T_B is intrinsic with large polaron holes as the principal charge carriers; they conduct via a band mechanism. The energy band gap lies in the range 3.2 to 4.0 eV, and the charge carrier mobility in the range 3.8×10^?2 to 2.5 cm²/V-Sec for the different tungstates. Below T_B both electronic and ionic conduction are extrinsic. The electrons conduct via a thermally activated hopping mechanism with an activation energy lying in the range 0.87 to 1.30 eV, and the holes via a diffusion process with an activation energy lying in the range 0.88 to 1.23 eV for the different tungstates.     

Study on electrical transport and photoconductivity in iodine-doped cellulose fibers

The electrical transport and photoconductivity of pure and iodine-doped cellulose fibers have been studied. The studies were conducted in the temperature range 293–363 K, while the electric field was varied over the range 1–100 V cm⁻¹. The conductivity of the iodine-doped cellulose fibers shows significant enhancement by more than four orders of magnitude as compared to undoped samples. The analysis reveals that the electrical conduction follows Ohm’s law for iodine-doped samples, while for the undoped samples the bulk-limited Pool–Frenkel conduction mechanism is likely to dominate for the steady state current. Especially, the clear photoconduction response at UV and visible region indicates that photoconduction is essential due to band-to-band electron–hole pair’s generation and that doped CF is a good conductor of photogenerated carriers.     

Temperature effects on electrical transport in semiconducting nanoporous carbon nanowires

In this paper we report on the effect of temperature on the electrical conductivity of amorphous and nanoporous (pores size around 0.5?nm) carbon nanowires. Poly(furfuryl alcohol) nanowires with diameter varying from 150 to 250?nm were synthesized by a template-based technique and upon pyrolysis yielded amorphous carbon nanowires with nanosized pores in them. We observed significant (as high as 700%) decrease in electrical resistance when the nanowire surface temperature was increased from room temperature to 160?°C. On the basis of the experimental and microscopy evidence, we infer a thermally activated carrier transport mechanism to be the primary electrical transport mechanism, at elevated temperatures, in these semiconducting, amorphous, and nanoporous carbon nanowires.     

Phase formation, chemical composition and electrical studies of Ti/Si bilayer system

The annealing effects over a range of temperatures of the titanium film (90 nm) grown on Si(111) by electron gun evaporation technique were investigated using physical and electrical measurements. Grazing Incidence X-ray Diffraction experiment shows a stable titanium disilicides formation at higher annealing temperature. The depth profiling data using X-ray Photoelectron Spectroscopy show that the properties are closely related to the change of the interfacial layer and chemical state under the high-temperature annealing. The Schottky Barrier Height, as estimated by the current-voltage measurement is 0.75, 0.695, 0.662 and 0.60 eV for pristine and annealed samples at 450, 550 and 700 °C respectively.     

Anomalous electrical transport behavior in nanocrystalline nickel

We have prepared nanocrystalline Ni (n-Ni) samples of grain sizes 40-100?nm using a polyol method and investigated the electrical transport on their compacted pellets in the temperature range 3-300?K. The resistivity, ρ, decreases nearly linearly with increase in compaction pressure but without a change in its slope, dρ/dT. ρ is anomalously large, and is strongly temperature and grain-size dependent. The resistivity at room temperature, ρ(300?K), is in the range ～40-759?μΩ?cm but with a positive coefficient of resistivity α (metallic). This is associated with the significantly enhanced dρ/dT with increase in residual resistivity ρ(0). These characteristics are attributed to the disorder in the grain boundaries that represents effectively a series resistor network.