Microstructural transformation of vanadium pentoxide powder obtained by high-energy vibrational ball-milling

An X-ray powder profile analysis of vanadium pentoxide powder milled in a high-energy vibrational ball-mill is presented. The strain- and size-induced broadening of the Bragg reflection for two different crystallographic directions ([001] and [100]) were determined by Warren-Averbach (WA) analysis, using a pattern-decomposition method assuming a pseudo-Voigt function. The deformation process causes a decrease in the domain size, and a near isotropic saturation value of similar to 10 nm is reached after severe milling. The initial stages of milling produce a propensity for size broadening, whereas, with increasing milling time, microstrain broadening is predominant. WA analysis indicated significant plastic strain along with spatial confinement of the internal strain fields, probably in the crystallite interfaces. Transmission electron microscopy revealed a drastic change in particle shape after 64 h of milling, indicating the existence of size anisotropy which, however, decreased with further increase of the milling time

"The fruits of independence": Satyajit Ray, Indian nationhood and the spectre of empire

Challenging the longstanding consensus that Satyajit Ray's work is largely free of ideological concerns and notable only for its humanistic richness, this article shows with reference to representations of British colonialism and Indian nationhood that Ray's films and stories are marked deeply and consistently by a distinctively Bengali variety of liberalism. Drawn from an ongoing biographical project, it commences with an overview of the nationalist milieu in which Ray grew up and emphasizes the preoccupation with colonialism and nationalism that marked his earliest unfilmed scripts. It then shows with case studies of Kanchanjangha (1962), Charulata (1964), First Class Kamra (First-Class Compartment, 1981), Pratidwandi (The Adversary, 1970), Shatranj ke Khilari (The Chess Players, 1977), Agantuk (The Stranger, 1991) and Robertsoner Ruby (Robertson's Ruby, 1992) how Ray's mature work continued to combine a strongly anti-colonial viewpoint with a shifting perspective on Indian nationhood and an unequivocal commitment to cultural cosmopolitanism. Analysing how Ray articulated his ideological positions through the quintessentially liberal device of complexly staged debates that were apparently free, but in fact closed by the scenarist/director on ideologically specific notes, this article concludes that Ray's reputation as an all-forgiving, ‘everybody-has-his-reasons’ humanist is based on simplistic or even tendentious readings of his work

Phase-transformations in amorphous 3Al2O3-2SiO2 system prepared by sol-gel method

Binary gels of SiO2-Al2O3 of different compositions were prepared, using alkoxides, by the sol-gel technique. In this communication, we report the preparation and phase-transformations of 3Al2O3-2SiO2 (mullite) gel. The material obtained was dried and heat-treated at different temperatures for dehydration-polymerization. Further heat-treatment above 900°C promoted crystallization, a metastable phase first being formed leading to the stable mullite phase. The kinetics and the microstructural evolution of these transformations were studied by X-ray diffraction, differential thermal analysis, electron microscopy, infrared spectroscopy and refractive index measurements. It was found that in this gel material the high-temperature heat-treatment at 1450°C produced pure well-crystallized mullite (particle size ∼ 0.07–0.15 μm) of prismatic shape contrary to its characteristic acicular habit

Effect of substrate temperature and annealing temperature on the structural, electrical and microstructural properties of thin Pt films by rf magnetron sputtering

Influence of both substrate temperature, T-s, and annealing temperature, T-a, on the structural, electrical and microstructural properties of sputtered deposited Pt thin films have been investigated. X-ray diffraction results show that as deposited Pt films (T-s = 300, 400 degrees C) are preferentially oriented along (1 1 1) direction. A little growth both along (2 0 0) and (3 1 1) directions are also noticed in the as deposited Pt films. After annealing in air (T-a = 500-700 degrees C), films become strongly oriented along (1 1 1) plane. With annealing temperature, average crystallite size, D, of the Pt films increases and micro-strain, e, and lattice constant, a(0), decreases. Residual strain observed in the as deposited Pt films is found to be compressive in nature while that in the annealed films is tensile. This change in the strain from compressive to tensile upon annealing is explained in the light of mismatch between the thermal expansion coefficients of the film material and substrate. Room temperature resistivity of Pt films is dependant on both the T-s and T-a of the films. Observed decrease in the film resistivity with T-a is discussed in terms of annihilation of film defects and grain-boundary. Scanning electron microscopic study reveals that as the annealing temperature increases film densification improves. But at an annealing temperature of similar to 600 degrees C, pinholes appear on the film surface and the size of pinhole increases with further increase in the annealing temperature. From X-ray photoelectron spectroscopic analysis, existence of a thin layer of chemisorbed atomic oxygen is detected on the surfaces of the as deposited Pt films. Upon annealing, coverage of this surface oxygen increases. (c) 2006 Elsevier B.V. All rights reserved

A simple spectrophotometric method for determination of the optical constants and band gap energy of multiple layer TiO2 thin films

Using sol-gel processing, TiO2 films have been prepared on microscopic glass slides by dip-coating technique. From X-ray diffractometric (XRD) and X-ray photoelectron spectroscopic (XPS) measurements, it has been confirmed that the deposited films are an anatase form of stoichiometric TiO2. Using either normal incidence transmittance or normal incidence reflectance data, a simple method for determining both film refractive index, n(lambda), and film thickness, d, has been proposed for a transparent film on a non-absorbing flat substrate. At same wavelength within visible region, a correlation between T-S and T-B has been established and verified. T-S and T-B represent the transmittances of single side and both sides coated films of same thickness, respectively, prepared at identical conditions. Average film thickness per coating at various withdrawal speeds (58-146 mm min(-1)) has been estimated. An empirical dispersion equation that describes the variation of n(lambda) of TiO2 films in the wavelength (lambda) range of similar to390-800 nm has been deduced. Band gap energy (E-g) has also been estimated for these films. It has been observed that E-g changes from similar to3.35 to 3.16 eV as the film thickness varies from similar to100 to 300 nm and it does not depend significantly upon film withdrawal speeds in the range 58-146 mm min(-1). (C) 2003 Elsevier B.V. All rights reserved

Influence of calcination ambient and film thickness on the optical and structural properties of sol-gel TiO2 thin films

Influence of both calcination ambient and film thickness on the optical and structural properties of sol-gel derived TiO2 thin films have been studied. X-ray diffraction results show that prepared films are in an anatase form of TiO2. Films calcined in argon or in low vacuum (similar to 2 x 10(-1) mbar) are found to be smaller in crystallite size, more transparent at low wavelength region of similar to 300-450 nm, denser, have higher refractive index and band gap energy compared to air-calcined films. Scanning electron microscopic study reveals that surfaces of TiO2 films calcined in argon or in low vacuum are formed by densely packed nano-sized particulates. Presence of voids and signs of agglomeration can be seen clearly in the surface microstructure of air-calcined films. In the thickness range similar to 200-300 nm, band gap energy and crystallite size of TiO2 films remain practically unaffected with film thickness but refractive index of thinner film is found to be marginally higher than that of thicker film. In this work, it has been shown that apart from temperature and soaking time, partial pressure of oxygen of the ambient is also an important parameter by which crystallite size, microstructure and optical properties of the TiO2 films may be tailored during calcination perio

The formation of intermetallics in Cu/In thin-films

The kinetics of the formation of intermetallics in the Cu-In bimetallic thin film couple have been studied from room temperature to 432 K by measuring the evolution of composite and contact electrical resistance with time and temperature. The resistivity measurements have been supplemented by x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Copper reacts with indium even at room temperature to form CuIn intermetallic and assuming a model of defect assisted diffusion into the grains, the activation energy averaged over five different samples is found to be 0.40 eV. The grain boundary diffusion is found to occur with an average activation energy of 0.55 eV. XRD confirms the growth of CuIn intermetallic and on annealing at higher temperature, for copper-rich films copper further reacts with CuIn to form Cu9In4. Further evidences of solid state reactions and grain boundary diffusion through Cu grain boundaries have been obtained from SEM study. TEM indicates the growth of the grain size on annealing and confirms the presence of the CuIn phase

Interfacial reactions in Ag-Zn thin-film couples

Interfacial reactions in Agsingle bondZn thin film couples have been investigated by measuring the contact resistance and composite electrical resistance with time and temperature in order to understand the kinetic behaviour of the system. The resistivity measurements have been supplemented by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The activation energy of diffusion has been found to be 6.1 × 10−20 J from electrical resistivity measurements where the model assumes rapid grain boundary diffusion followed by a defect-assisted path for diffusion into the grain and 8.3 × 10−20 J from contact resistance measurements where the model is based on grain boundary diffusion. XRD indicates the growth of ß′-Agsingle bondZn phase even at room temperature which changes to the ß phase above 250°C. SEM confirms the diffusion of silver through zinc grain boundaries, especially at the interface boundary. TEM indicates the growth of grain size with annealing and confirms the presence of the ß′ phase

Rietveld analysis of polymorphic transformations of ball milled anatase TiO2

Rietveld's whole powder profile fitting method based on crystal structure refinement is applied to extract the microstructure information of several polymorphic TiO2 phases grown simultaneously during high energy vibratory ball milling of anatase phase. Warren-Averbach's method of X-ray line profile analysis is also made for comparison of above results. The X-ray powder patterns of four TiO2 phases along with alpha-Al2O3 (contamination) are simulated simultaneously for the first time to fit the experimental X-ray powder patterns of multiphase materials. The structural details of monoclinic TiO2 (B) phase are also reported first time in this paper. The advantages of the present method of analysis over the other methods of X-ray line profile analysis are discussed in details. (C) 2002 Elsevier Science B.V. All rights reserved

Influence of chemical composition, phase and thickness of TiO(x) (x <= 2) seed layer on the growth and orientation of the perovskite phase in sputtered PZT thin films

To study the influence of TiO(x) (x <= 2) seed layer on the formation of perovskite phase in lead zirconate titanate [Pb(Zr(0.52)Ti(0.48))O(3)] thin films, TiOx films of thickness similar to 20-480nm were prepared on coming-1737 glass substrates by r.f. magnetron sputtering and then post-annealed in air at different temperatures (350-650 degrees C). Depending mainly on seed layer thickness, TiO(x) films transform either into anatase or rutile TiO(2) after air-annealing. Thin PZT films (similar to 150 nm)were then deposited on substrates pre-coated with TiO(x) seed layers and air-annealed at 650 degrees C. It is found that thin TiO(2) seed layers (<= 150 nm) promote perovskite phase formation in PZT films. Anatase TiO(2) promotes the growth of randomly oriented perovskite PZT. A (101) textured rutile TiO(2) of thickness similar to 100 nm favours the growth of highly oriented perovskite phase along (100) and surface morphology of these PZT films shows dense rosette structures. A TiO or an amorphous TiO(x) seed film does not initiate perovskite growth. As the thickness of the TiO(x) seed layer exceeds similar to 150 nm, perovskite phase does not form readily irrespective of the crystalline form/phase of TiO(x). Thus, chemical composition, crystalline phase and thickness of the TiC(x) seed layer influence remarkably the crystalline phase, texture and surface morphology of the grown PZT films. (C) 2008 Elsevier B.V. All rights reserved