Volume 29, Issue 7
December 2006, pages 653-741
pp 653-657 December 2006 Semiconductors
Al–Sb bilayer thin films having various thicknesses were deposited by thermal evaporation on ITO-coated conducting glass substrates at a pressure of 10-5 torr. These films were irradiated by Ag12+ heavy ions of energy, 160 MeV, with a fluence of 2.2 × 1013 ions/cm2, to get aluminum antimonide semiconductor. Rutherford back scattering and optical band gap data confirmed mixing of bilayer to form the semi-conducting system.
pp 659-663 December 2006 Semiconductors
In the present study, 𝑝-type (Bi2Te3)𝑥(Sb2Te3)1–𝑥 crystals with various chemical compositions (𝑥 = 0.2, 0.22, 0.235, 0.25, 0.265, 0.28 and 0.3) were fabricated through the zone melting method. Thermoelectric properties, including Seebeck coefficient (𝛼), electrical conductivity (𝜎), thermal conductivity (𝜅) and Hall constants, were measured at room temperature, 300 K. The influence of the variations of Bi2Te3 content (𝑥) on the thermoelectric properties was studied. The increase of Bi2Te3 content (𝑥) caused a decrease in (carrier) hole concentration and thus a decrease of 𝜎 and an increase of 𝛼. The maximum figure of merit (𝑍 = 𝛼2\𝜎/𝜅) of 2.7 × 10-3 K-1 was obtained at about 300 K for the composition of 25% Bi2Te3–75% Sb2Te3 with 3wt% excess of Te.
pp 665-671 December 2006 Solid State Ionics
Novel amorphous zirconium (IV) phosphonates of the class of tetravalent metal acid (TMA) salts have been synthesized by sol–gel method where phosphonates used are hydroxy ethylidene diphosphonic acid (HEDP), amino tri(methylene phosphonic acid) (ATMP) and diethylenetriamine penta(methylenephosphonic acid) (DETPMP) to give ZrHEDP, ZrATMP and ZrDETPMP, respectively. These materials have been characterized for elemental analysis, Zr and P (ICP-AES) and carbon, hydrogen, nitrogen contents (CHN analyser), thermal analysis (TGA, DSC), X-ray analysis and FTIR spectroscopy. Chemical resistivity of these materials has been accessed in acids, bases and organic solvent media. The protons present in the structural hydroxyl groups indicate good potential for TMA salts to exhibit solid state proton conduction. The transport properties of these materials has been explored by measuring specific proton conductance at different temperatures in the range 30–120°C at 10°C intervals, using SOLARTRON DATASET impedance analyser (SI 1260) over a frequency range 1 Hz–10 MHz at a signal level below 1 V. Based on the specific conduction data and Arrhenius plots, a suitable mechanism has been proposed and conductance performance of zirconium phosphonates compared with zirconium phosphate (ZrP).
pp 673-678 December 2006 Polymers
An investigation is carried out on gel polymer electrolytes consisting of poly (vinylidene fluoride) (PVdF) as a host polymer, lithium perchlorate (LiClO4), lithium triflate (LiCF3SO3) as salts and mixture of ethylene carbonate (EC) and propylene carbonate (PC) as plasticizers. Polymer thin films were prepared by solvent casting technique and the obtained films were subjected to different characterizations, to confirm their structure, complexation and thermal changes. X-ray diffraction revealed that the salts and plasticizers disrupted the crystalline nature of PVdF based polymer electrolytes and converted them into an amorphous phase. TG/DTA studies showed the thermal stability of the polymer electrolytes. The role of interaction between polymer hosts on conductivity is discussed using the results of a.c. impedance studies. Room temperature (28°C) conductivity of 2.786 × 10-3 Scm-1 was observed in PVdF (24)–EC/PC (68)–LiCF3SO3 (2)/LiClO4 (6) polymer system.
pp 679-684 December 2006 Alloys
Equal channel angular pressing (ECAP) is a novel technique for producing ultra fine grain structures in submicron level by introducing a large amount of shear strain into the materials without changing the billet shape or dimensions. This process is well suited for aluminium alloys and is capable of producing ultra fine grain structures with grain sizes falling between 200 and 500 nm. The present study attempts to apply ECAP technique to 99.5% pure aluminium and characterize the resulting aluminium by optical metallography, atomic force microscopy (AFM) and hardness measurement. ECAP of 99.5% pure aluminium produces ultrafine grain structure of about 620 nm after 8 passes. Despite an increase in the hardness from 23 to 47 BHN up to 6 passes, it decreases slightly for seventh and eighth passes. The results are compared with the already existing results available on pure aluminium. Analysis of the results of this investigation with those available in the literature has revealed that the number of passes essential to achieve a homogeneous microstructure in pure Al increases, while the ultimate equilibrium grain size obtained becomes finer with decreasing purity.
pp 685-688 December 2006 Alloys
Friction factor has been determined for CP aluminium and aluminium–zinc alloys using ring compression test at different temperatures from 303 K to 773 K. It is found that CP aluminium exhibits sticking whereas Al–Zn alloys do not exhibit sticking at elevated temperatures. Hot working of Al–Zn alloy is easier than that of CP aluminium at 773 K. As zinc content increases up to 10 wt% the friction factor decreases up to 0.02.
pp 689-692 December 2006 Composites
Three kinds of LiFePO4/C composites for lithium-ion batteries were prepared by solid-state reaction. The crystalline structure, morphology and specific surface area of the composites were investigated by X-ray diffraction, scanning electron microscopy and multi-point Brunauer, Emmett and Teller. The results showed that the samples were all well-ordered olivine structures. A network structure, LiFePO4/C composite, was obtained using phenolic resin as carbon source. It possessed the highest specific surface area of 115.65 m2/g, exhibited the highest discharge capacity of 164.89 and 149.12 mAh/g at 0.1 C and 1 C rates, respectively. The discharge capacity was completely recovered when 0.1 C rate was applied again.
pp 693-700 December 2006 Thin Films
We report the effect of interlayer on multilayer X-ray reflectivity (XRR) profile using simulations at 8.047 keV (CuK𝛼) energy. We distinguished the effect of interfacial roughness and in-depth interlayer on reflectivity profile. The interfacial roughness reduces the intensity of individual peak while the in-depth interlayer redistributed the reflectivity profile. We are able to discern the asymmetry in interlayer thickness at two interfaces if the interfacial roughness is small compared to in-depth interlayer thickness. The limitation is that, the sensitivity decreases with increasing interfacial roughness. This interlayer model is applied for electron beam evaporated Mo/Si multilayers. The Mo–on–Si interlayer thickness is 10 ± 0.5 Å and Si–on–Mo interlayer thickness is 8 ± 0.5 Å. The nature of interfacial compound is identified using X-ray photoelectron spectroscopy (XPS). The mechanism of interlayer asymmetry is explained on the basis of different heats of sublimation of Mo and Si.
pp 701-704 December 2006 Nanomaterials
Carbon nanotubes (CNTs) have been synthesized via directly pyrolyzing ferrocene in the autoclave. The nanotubes with several micrometers in length have outer and inner diameters in the range of 40–100 nm and 20–40 nm, respectively. An yield of ∼70% of CNTs can be obtained without any accessorial solvents and catalysts. Experimental results showed that a temperature higher than 600°C in conjunction with proper pressure was favourable for achievement of the nanotubes. The growth mechanism of CNTs was also discussed.
pp 705-708 December 2006 Nanomaterials
TiO2 nanotubes have been synthesized by sol–gel template method using alumina membrane. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, UV absorption spectrum and X-ray diffraction techniques have been used to investigate the structure, morphology and optical properties of TiO2 nanotubes. SEM image showed that TiO2 nanotubes obtained were ordered and uniform. The diameter and length of the nanotubes were decided by the pore size and thickness of alumina template. Raman and XRD measurements confirmed the crystallinity and anatase phase of the TiO2 nanotubes. The optical absorption measurement of TiO2 nanotubes exhibits a blue shift with respect to that of the bulk TiO2 owing to the quantum size effect.
pp 709-716 December 2006 Nanomaterials
Nanostructured copper oxide thin films (CuO) were prepared on conducting glass support (SnO2: F overlayer) via sol–gel starting from colloidal solution of copper (II) acetate in ethanol. Films were obtained by dip coating under room conditions (temperature, 25–32°C) and were subsequently sintered in air at different temperatures (400–650°C). The evolution of oxide coatings under thermal treatment was studied by glancing incidence X-ray diffraction and scanning electron microscopy. Average particle size, resistivity and band gap energy were also determined. Photoelectrochemical properties of thin films and their suitability for splitting of water were investigated. Study suggests that thin films of CuO sintered at lower temperatures (≈ 400°C) are better for photoconversion than thick films or the films sintered at much higher temperatures. Plausible explanations have been provided.
pp 717-720 December 2006 Nanomaterials
While there is overwhelming evidence that strengthening from grain size refinement persists into the nanocrystalline grain size regime consistent with extrapolation of classical Hall–Petch (H–P) behaviour, there are indications of a transition to an inverse H–P dependence, i.e. grain boundary weakening behaviour, occurring below a grain size of ∼ 10–20 nm. When Hall–Petch strengthening predominates, and the stress intensity, i.e. H–P slope value, 𝑘𝜀, is thermally-activated (as is the case for pure fcc and the easy basal slip hcp metals), the strain rate sensitivity, defined as [𝜕𝜎/𝜕 ln(d𝛾/d𝑡]𝑇, also is predicted to follow an H–P type dependence, thus, increasing with decrease in grain size. As a consequence, the activation volume that is inversely proportional to the strain rate sensitivity, is found to decrease by an order of magnitude, from around 1000 b3 in conventional grain size fcc Cu and Ni materials to 10–100 b3, for nanomaterials. At the smallest grain sizes, the transition to an inverse H–P dependence has been proposed to occur because of onset of effective high temperature grain boundary weakening behaviour that is well known in limiting creep property descriptions. If the inverse H–P effect (grain boundary weakening) is genuine, we predict that the strain rate sensitivity and corresponding inverse activation volume dependence on grain size should also have to show a reversal.
pp 721-733 December 2006
pp 734-741 December 2006
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