Optical and electrical properties of SnO2 films prepared by chemical vapour deposition

Transparent and conducting SnO₂ films are prepared at 500°C on quartz substrates by chemical vapour deposition technique, involving oxidation of SnCl₂. The effect of oxygen gas flow rate on the properties of SnO₂ films is reported. Oxygen with a flow rate from 0·8–1·35 lmin⁻¹ was used as both carrier and oxidizing gas. Electrical and optical properties are studied for 150 nm thick films. The films obtained have a resistivity between 1·72 × 10⁻³ and 4·95 × 10⁻³ ohm cm and the average transmission in the visible region ranges 86–90%. The performance of these films was checked and the maximum figure of merit value of 2·03 × 10⁻³ ohm⁻¹ was obtained with the films deposited at the flow rate of 1·16 lmin⁻¹.     

Dielectric and pyroelectric properties of a composite of ferroelectric ceramic and polyurethane

Flexible piezo- and pyroelectric composite was made in the thin film form by spin coating. Lead Zirconate Titanate (PZT) ceramic powder was dispersed in a castor oil-based polyurethane (PU) matrix, providing a composite with 0–3 connectivity. The dielectric data, measured over a wide range of frequency (10^–5 Hz to 10⁵ Hz), shows a loss peak around 100 Hz related with impurities in the polymer matrix. There is also an evidence of a peak in the range 10^–4 Hz, possibly originating from the glass transition temperature T_g of the polymer. The pyroelectric coefficient at 343 K is 7.0×10^–5 C·m^–2·K^–1 which is higher than that of β-PVDF (1×10^–5 C·m^–2·K^–1). Electronic Publication     

Hydrodynamics and heat transfer in cooling systems with intersecting channels. 3. Effect of the angle of flow and the number of stages

Results of further investigation of some variants of wafer structures are given. The effect of the angle of flow on the hydraulic resistance and heat transfer at Re numbers of 1·10²–2·10⁴ is revealed. The temperature field of a two-stage system is analyzed. It is shown that a size reduction of the structure and an increase in the number of stages make it possible to obtain the maximum possible coefficient of reduced heat transfer (2.5–2.8)·10⁵ W/(m²·K). Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 73, No. 2, pp. 214–223, March–April, 2000.     

Reduction of aluminum oxide in a nonequilibrium hydrogen plasma

A new method is proposed and experimental investigations are carried out aimed at reducing aluminum oxide in a nonequilibrium hydrogen plasma of a combined glow discharge (CGD) at a pressure of 1315.8–13,158 Pa, a discharge current of 5·10⁻²–3 A, and a hydrogen flow rate of 10⁻⁶–10⁻⁴ nm³/sec. A high degree of conversion of the aluminum oxide (60%) with an energy consumption of 20 kW·h/kg of Al₂O₃ is attained. Reduction of metals from oxides and other compounds in a CGD nonequilibrium hydrogen plasma can be used for producing rare-earth and high-purity metals. Translated from Inzhenerno-Fizcheskii Zhurnal, Vol. 73, No. 3, pp. 580–584, May–June, 2000.     

Precision equipment for reproducing particle sizes and numerical concentrations in aerosols, suspensions, and powders

Precision equipment is described for reproducing the unit of numerical concentration and size for particles in aerosols, suspensions, and powders in the concentration range from 4·10⁷ to 4·10¹³ m⁻³ with average particle dimensions of 1–100 μm. The apparatus is based on small-angle laser-beam scattering and Beer's law. The optical system is described. The residual systematic error in reproducing the numerical concentration and unit does not exceed 12% in the above concentration and size ranges. Translated from Izmeritel'naya Tekhnika, No. 9, pp. 68–70, September, 1997     

Structure and Features of the Motion of a Cathode Spot on a Continuous Titanium Cathode

High-speed video filming by the VS-FAST-NG CCD-array-based video camera from the firm of Videoskan with speeds of 1000 and 5000 frames per second and exposure time of 1·10⁻³ and 2·10⁻⁴ sec, respectively, is conducted. It is established that the arc burns from two or three cathode spots for (1–1.2)·10⁻³ sec. The mean and local speeds of the group of cathode spots are determined. If there is no external magnetic field present, the mean speed is equal to 5–6 m/sec. If there is a magnetic field B = 0.005 T present, the mean speed is equal to 15–16 m/sec. __________ Translated from Izmeritel'naya Tekhnika, No. 10, pp. 42–44, October, 2005.     

Structural characterization of lead sulfide thin films by means of X-ray line profile analysis

X-ray diffraction patterns of chemically deposited lead sulphide thin films have been recorded and X-ray line profile analysis studies have been carried out. The lattice parameter, crystallite size, average internal stress and microstrain in the film are calculated and correlated with molarities of the solutions. Both size and strain are found to contribute towards the broadening of X-ray diffraction line. The values of the crystallite size are found to be within the range from 22–33 nm and the values of strain to be within the range from 1·0 × 10⁻³–2·5 × 10⁻³.     

Waveguide-dielectric resonator method for accurate measurement of parameters of materials at high frequencies

The theory is given, with an analysis and various examples, of the practical implementation of a method for measuring the relative permittivity ɛ^*=ɛ′−iɛ″ of materials in the 0.5–26-GHz frequency range. The results and experimental errors are given of measurements of ε′ in the range 2–200 and of tanδ in the range from 5·10⁻⁵ to 2·10⁻². Translated from Izmeritel'naya Tekhnika, No. 6, pp. 62–66, June, 1999.     

Photoelectric method of measuring the rotation period of a turbine drive shaft

The rotation period has been measured for a turbine shaft in a thermal power station by an optoelectronic method. The electronic unit is screened from electromagnetic interference at line frequency, and the fiber-optic lines provide a measurement error of 5·10⁻⁴%. Translated from Izmeritel'naya Tekhnika, No. 12, pp. 28–29, December, 1996.     

Size quantization effects in optical and electrical properties of II–VI semiconductor films in nanocrystalline form

The electrical properties of CdTe and optical properties of ZnS in nanocrystalline thin film form are studied with a view to have a clearer understanding of the optical processes and the carrier transport mechanisms in nanocrystalline II–VI semiconductors, in general. Nanocrystalline ZnS and CdTe films were deposited by magnetron sputtering of respective targets in argon plasma. The optical absorption data of nanocrystalline ZnS films (thickness 10–40 nm) could be explained by the combined effects of phonon and inhomogeneity broadening along with optical loss due to light scattering at the nanocrystallites. The conductivity of CdTe (grain size within 4–4·7 nm) showed (T ₀/T) ^p dependence withp ∼ 0·5 indicating the presence of a Coulomb gap near the Fermi level. The width of the Coulomb gap varied within 0·02–0·04 eV depending on the deposition condition. The existing theoretical models were used for estimating hopping energy (0·02–0·04 eV) and hopping distance (2·8–5·1 nm) in nano CdTe films.     

Preparation, characterization and conductivity studies of Li3?2xAl2?xSbx(PO4)3

New NASICON type materials of composition, Li_3−2x Al_2−x Sb _x (PO₄)₃ (x = 0·6 to 1·4), have been prepared and characterized by powder XRD and IR. D.C. conductivities were measured in the temperature range 300–573 K by a two-probe method. Impedance studies were carried out in the frequency region 10²−10⁶ Hz as a function of temperature (300–573 K). An Arrhenius behaviour is observed for all compositions by d.c. conductivity and the Cole-Cole plots obtained from impedance data do not show any spikes on the lower frequency side indicating negligible electrode effects. A maximum conductivity of 4·5 × 10⁻⁶ S cm⁻¹ at 573 K was obtained for x = 0·8 of the Li_3−2x Al_2−x Sb _x (PO₄)₃ system.     

Investigation of active slip-systems in some body-centered cubic metals

Tensile tests were performed on high-purity W and Mo polycrystals at room temperature for a range of axial strain-rates 2.1 × 10⁻⁴–2.1 × 10⁻² s⁻¹. The critical resolved shear stress (CRSS) data was analyzed by using the analytical formulation for the strain-rate dependence of the CRSS derived in the kink-pair nucleation (KPN) model of flow stress in crystals with high intrinsic lattice friction. On evaluation of various microscopic slip-parameters of the model, the active slip-system in both W and Mo polycrystals was identified as {110}〈111〉. This is in good agreement with that deduced from the published data on the temperature dependence of the CRSS of these crystals as well as from the observed slip-lines on the deformed crystals reported in the literature. Moreover, the available data on the temperature dependence of the CRSS of Mo, Nb, Fe, V, and K crystals were also analyzed within the framework of the KPN model of flow stress. Peierls mechanism was found to be responsible for the CRSS of these metals; the active slip-systems in refractory metals Mo, Nb, Fe, and V were {110}〈111〉 and {211}〈111〉 whereas that in alkali metal K was {321}〈111〉.     

Effect of transient change in strain rate on plastic flow behaviour of low carbon steel

Plastic flow behaviour of low carbon steel has been studied at room temperature during tensile deformation by varying the initial strain rate of 3·3 × 10⁻⁴s⁻¹ to a final strain rate ranging from 1·33 × 10⁻³s⁻¹ to 2 × 10⁻³s⁻¹ at a fixed engineering strain of 12%. Haasen plot revealed that the mobile dislocation density remained almost invariant at the juncture where there was a sudden increase in stress with a change in strain rate and the plastic flow was solely dependent on the velocity of mobile dislocations. In that critical regime, the variation of stress with time was fitted with a Boltzmann type Sigmoid function. The increase in stress was found to increase with final strain rate and the time elapsed in attaining these stress values showed a decreasing trend. Both of these parameters saturated asymptotically at a higher final strain rate.     

Hot deformation behavior of an 8% Cr cold roller steel

An 8% Cr cold roller steel was compressed in the temperature range 900–1200 °C and strain rate range 0.01–10 s⁻¹. The mechanical behavior has been characterized using stress–strain curve analysis, kinetic analysis, processing maps, etc. Metallographic investigation was performed to evaluate the microstructure evolution and the mechanism of flow instability. It was found that the work hardening rate and flow stress decreased with increasing deformation temperature and decreasing strain rate in 8% Cr steel; the efficiency of power dissipation decreased with increasing Z value; flow instability was observed at higher Z-value conditions and manifested as flow localization near the grain boundary. The hot deformation equation and the dependences of critical stress for dynamic recrystallization and dynamic recrystallization grain size on Z value were obtained. The suggested processing window is in the temperature range 1050–1200 °C and strain rate range 0.1–1 s⁻¹ in the hot processing of 8% Cr steel.     

Thickness dependent electrical properties of CdO thin films prepared by spray pyrolysis method

A large number of thin films of cadmium oxide have been prepared on glass substrates by spray pyrolysis method. The prepared films have uniform thickness varying from 200–600 nm and good adherence to the glass substrate. A systematic study has been made on the influence of thickness on resistivity, sheet resistance, carrier concentration and mobility of the films. The resistivity, sheet resistance, carrier concentration and mobility values varied from 1·56–5·72×10⁻³ Ω-cm, 128–189 Ω/□, 1·6–3·9×10²¹ cm⁻³ and 0·3–3 cm²/Vs, respectively for varying film thicknesses. A systematic increase in mobility with grain size clearly indicates the reduction of overall scattering of charge carriers at the grain boundaries. The large concentration of charge carriers and low mobility values have been attributed to the presence of Cd as an impurity in CdO microcrystallites. Using the optical transmission data, the band gap was estimated and found to vary from 2·20–2·42 eV. These films have transmittance around 77% and average reflectance is below 2·6% in the spectral range 350–850 nm. The films aren-type and polycrystalline in nature. SEM micrographs of the CdO films were taken and the films exhibit clear grains and grain boundary formation at a substrate temperature as low as 523 K.     

A laser-based automatic interference refractometer for control of the gradient of the index of refraction of plane-parallel glass elements

A laser-based fiber-optic interference refractometer for use in automatic control of the gradient of the index of refraction of large plane-parallel glass optical elements with resolution on the order of 8·10^–7 cm^–1 and absolute error at most 2·10^–5 cm^–1 is proposed.     

Li-storage and cycling properties of spinel,CdFe<Subscript>2</Subscript>O<Subscript>4</Subscript>, as an anode for lithium ion batteries

Cadmium ferrite, CdFe₂O₄, is synthesized by urea combustion method followed by calcination at 900°C and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) techniques. The Li-storage and cycling behaviour are examined by galvanostatic cycling, cyclic voltammetry (CV) and impedance spectroscopy in the voltage range, 0·005–3·0 V vs Li at room temperature. CdFe₂O₄ shows a first cycle reversible capacity of 870 (± 10) mAhg⁻¹ at 0·07C-rate, but the capacity degrades at 4 mAhg⁻¹ per cycle and retains only 680 (± 10) mAhg⁻¹ after 50 cycles. Heat-treated electrode of CdFe₂O₄ (300°C; 12 h, Ar) shows a significantly improved cycling performance under the above cycling conditions and a stable capacity of 810 (± 10) mAhg⁻¹ corresponding to 8·7 moles of Li per mole of CdFe₂O₄ (vs theoretical, 9·0 moles of Li) is maintained up to 60 cycles, with a coulombic efficiency, 96–98%. Rate capability of heat-treated CdFe₂O₄ is also good: reversible capacities of 650 (± 10) and 450 (± 10) mAhg⁻¹ at 0·5 C and 1·4 C (1 C = 840 mAg⁻¹) are observed, respectively. The reasons for the improved cycling performance are discussed. From the CV data in 2–15 cycles, the average discharge potential is measured to be ∼0·9 V, whereas the charge potential is ∼2·1 V. Based on the galvanostatic and CV data, ex situ-XRD, -TEM and -SAED studies, a reaction mechanism is proposed. The impedance parameters as a function of voltage during the 1st cycle have been evaluated and interpreted. Dedicated to Prof. C N R Rao on his 75th birthday, and his contributions to science for the past 56 years     

High-frequency actuator control of air flow near a circular cylinder: Impact of the discharge parameters on the cylinder aerodynamic drag

The impact of capacitive high-frequency surface discharge on a flow around a circular cylinder is studied at airflow velocity of 20–100 m/s and the Reynolds numbers Re < 2.4 × 10⁵. The power of the discharge was modulated at a frequency of 10²–10⁴ Hz, corresponding to the Strouhal number St = 0.1–10. It is shown that the distribution of pressure in the wake behind the cylinder is significantly influenced by the discharge. A decrease in the average diameter of the wake is observed. The parameters of the discharge were measured: the gas temperature, heating rate in the discharge region, and velocity of discharge propagation.     

Size dependent optical characteristics of chemically deposited nanostructured ZnS thin films

ZnS thin films of different thicknesses were prepared by chemical bath deposition using thiourea and zinc acetate as S²⁻ and Zn²⁺ source. The effect of film thickness on the optical and structural properties was studied. The optical absorption studies in the wavelength range 250–750 nm show that band gap energy of ZnS increases from 3·68–4·10 eV as thickness varied from 332–76 nm. The structural estimation shows variation in grain size from 6·9–17·8 nm with thickness. The thermoemf measurement indicates that films prepared by this method are of n-type.