Novel features of rapidly quenched melts of Bi2(Ca,Sr) 3Cu2O8+δ

By roller quenching and water quenching melts of Bi2(Ca, Sr)3Cu2O8+δ, glasses have been obtained. These glasses exhibit two glass transitions as well as two crystallization transitions. Microwave absorption studies show the glass to be weakly superconducting at 77 K, probably due to the presence of ultramicrocrystallites. The glass on crystallization at 870 K gives the crystalline n=1 member of the homologous series Bi2(Ca, Sr)n+1CunO 2n+4 and the n=2 member on annealing at 1100 K. The glass route provides a unique means of obtaining the n=2 member of the series. On prolonged annealing of the glass at 1120 K, the n=3 member seems to be formed.

Infra-red spectra of crystalline chloroacetates of Cu, Ca, Sr, Ba and Pb

The infra-red spectra of Cu, Ca, Sr, Ba and Pb chloroacetates were studied in order to investigate the effect of co-ordination on the vibration spectra of the ligand. The shifts of the symmetric and antisymmetric COO− vibrational frequencies indicate a bridged structure as the most probable one for the complexes investigated. No linear relationship between the shifts of the COO− stretching frequencies and E/r (where E is the electron excitation energy and r the ionic radius) was observed. No systematic mass effect on these COO− frequencies also could be established.

Processing maps for hot-working of powder metallurgy 1100 Al-10 vol % SiC-particulate metal-matrix composite

The hot-working characteristics of the metal-matrix composite (MMC) Al-10 vol % SiC-particulate (SiCp) powder metallurgy compacts in as-sintered and in hot-extruded conditions were studied using hot compression testing. On the basis of the stress-strain data as a function of temperature and strain rate, processing maps depicting the variation in the efficiency of power dissipation, given by eegr = 2m/(m+1), where m is the strain rate sensitivity of flow stress, have been established and are interpreted on the basis of the dynamic materials model. The as-sintered MMC exhibited a domain of dynamic recrystallization (DRX) with a peak efficiency of about 30% at a temperature of about 500°C and a strain rate of 0.01 s�1. At temperatures below 350°C and in the strain rate range 0.001�0.01 s�1 the MMC exhibited dynamic recovery. The as-sintered MMC was extruded at 500°C using a ram speed of 3 mm s�1 and an extrusion ratio of 10ratio1. A processing map was established on the extruded product, and this map showed that the DRX domain had shifted to lower temperature (450°C) and higher strain rate (1 s�1). The optimum temperature and strain rate combination for powder metallurgy billet conditioning are 500°C and 0.01 s�1, and the secondary metal-working on the extruded product may be done at a higher strain rate of 1 s�1 and a lower temperature of 425°C.

Electronic structure of ${\rm Ca}_{1-x}{\rm Sr}_x{\rm VO}_3$: A tale of two energy scales

We investigate the electronic structure of Ca1-xSrxVO3 using photoemission spectroscopy. Core level spectra establish an electronic phase separation at the surface, leading to a distinctly different surface electronic structure compared to the bulk. Analysis of the photoemission spectra of this system allowed us to separate the surface and bulk contributions. These results help us to understand properties related to two vastly differing energy scales, namely the low-energy scale of thermal excitations ( $\sim\!k_{\rm B}T$) and the high-energy scale related to Coulomb and other electronic interactions.

Measurement of Gibbs energy of formation of Ca2PbO4 using a solid-state cell with three electrodes

Phase relations in the system Ca-Pb-O at 1100 K have been determined by equilibrating 18 compositions in the ternary and identifying the phases present in quenched samples by X-ray diffraction and energy dispersive X-ray analysis (EDX). Only one ternary compound Ca2PbO4 was found to be present. The compound coexists with CaO and PbO. The intermetallic compounds Ca2Pb, Ca5Pb3 and CaPb and liquid alloys are in equilibrium with CaO. The standard Gibbs energies of formation of Ca2PbO4 (880 - 1100 K) and Pb3O4 (770 - 910 K) were determined using solid-state cells based on yttria-stabilized zirconia as the solid electrolyte. Pure oxygen gas at 0.1 MPa was used as the reference electrode. For measurements on Ca2PbO4, a novel cell design with three electrodes in series, separated by solid electrolyte membranes, was used to avoid polarization of the electrode containing three solid phases. Two three-phase electrodes were used. The first absorbs the electrochemical flux of oxygen from the reference electrode to the measuring electrode. The other three-phase electrode, which is unaffected by the oxygen flux through the solid electrolyte, is used for electromotive force (EMF) measurement. The results from EMF studies were cross-checked using thermogravimetry (TG) under controlled oxygen partial pressures. The stability of Pb3O4 was investigated using a conventional solid-state cell with RuO2 electrodes. The results can be summarized by the following equations: 2CaO + PbO +1/2O(2) --> Ca2PbO4 Delta(r)G degrees/J mol(-1) = (- 128340 + 93.21 T/K) +/- 200 3PbO + 1/2O(2) --> Pb3O4 Delta(r)G degrees/J mol(-1) = (- 70060 + 77.5 T/K) +/- 150

Dielectric Studies of laser ablated Ca doped BaTiO3 thin films

Recently, there has been growing interest in Ca modified BaTiO3 structures due to their larger electro-optic coefficients for their use in optical storage of information over conventional BaTiO3 crystals. Barium Calcium Titanate (BCT) shows promising applications in advanced laser systems, optical interconnects and optical storage devices. BaTiO3 thin films of varied Ca (3 at. % - 15 at. %) doping were deposited using pulsed laser ablation (KrF excimer laser) technique over Pt/Si substrates. The stoichiometric and the compositional analysis were carried out using EDAX and SIMS. The dielectric studies were done at the frequency regime of 40 Hz to 100 kHz at different ambient temperatures from 200 K to 600 K. The BCT thin films exhibited diffuse phase transition, which was of a typical non lead relaxor behavior and had high dielectric constant and low dielectric loss. The phase transition for the different compositions of BCT thin films was near the room temperature, showing a marked departure from the bulk phase transition. The C - V and the hysteresis behavior confirmed the ferroelectric nature below the phase transition and paraelectric at the room temperature.

Socio-environmental impact of idol immersion: dimensions and directions

India possesses a diverse and rich cultural heritage and is renowned as a 'land of festivals'. These festivals attract massive community involvement paving way to new materials such as 'Plaster of Paris' being used for 'modernizing' the representation of idols with very little thought given to the issues of toxicity and environmental impacts. Another dimension to the whole issue is the plight of the artisans and the workers involved in the trade. Owing to the unorganized nature of the industry there is minimal or no guidelines pertaining-to the worker safety and health risks of the people involved. This paper attempts to address the complexities of the inherent hazards as a consequence of these socio-environmental issues and trace the scientific rationale in addressing them in a practical and pragmatic way.

Structure of a dimer of ageratochromene

A solid obtained in the dimerisation of ageratochromene (6,7-dimethoxy-2,2-dimethyl-1-benzopyran)(II) in the presence of acid has been shown to be 5,6,6a,6b,7,12b-hexahydro-1,2,10,11-tetramethoxy-5,5,7,7-tetramethylcyclopenta[1,2-c;5,4,3-de]bis[1]benzopyran (IV) by a study of its n.m.r. and mass spectra.

Infrared spectra of trichloroacetates of copper, calcium, strontium and barium

Infrared spectra of trichloroacetates of Cu, Ca, Sr and Ba were studied in order to investigate the effect of coordination on the vibration spectra of the ligand. The shifts of the antisymmetric and symmetric COO- stretching frequencies are explained on the basis of the type of co-ordination of the COO- group to the metal ion. From the spectra it is established that the coordination of the COO- group to metal is different for trichloroacetates and monochloroacetates.

Novel dielectric properties of glasses prepared by quenching melts of Bisingle bondCasingle bondSrsingle bondCusingle bondO cuprates

Glasses, prepared from the melts of Bi2(Ca, Sr)n+1 CunO2n+4 (n=1,2 and 3) have been characterized by various techniques. These glasses exhibit relatively high dielectric constants, high electrical conductivity, a ferroelectric-like dielectric hysteresis loop and pyroelectric effect at 300K. They also show weak microwave absorption at 77K.

Simulation of magnetovolume effects in Fe65Ni35 nanoparticles

We compare magnetovolume effects in bulk and nanoparticles by performing Monte Carlo simulations of a spin-analogous model with coupled spatial and magnetic degrees of freedom and chemical disorder. We find that correlations between surface and bulk atoms lead with decreasing particle size to a substantial modification of the magnetic and elastic behavior at low temperatures.

Processing of an α-2 aluminide alloy, Ti---24Al---11Nb

Compressive stress-strain curves have been generated over a range of temperatures (900-1100-degrees-C and strain rates (0.001-100 s-1) for two starting structures consisting of lath alpha2 and equiaxed alpha2 in a Ti-24Al-11Nb alloy. The data from these tests have been analysed in terms of a dynamic model for processing. The results define domains of strain rate and temperature in which dynamic recrystallization of alpha2 occurs for both starting structures. The rate controlling process for dynamic recrystallization is suggested to be cross-slip in the alpha2 phase. A region of processing instability has also been defined within which shear bands form in the lath structure. Recrystallization of the beta phase is shown to occur for different combinations of strain rate and temperature from those in which the alpha2 phase recrystallizes dynamically

Interface states of laser ablated BaTiO3 and Ba0.9Ca0.1TiO3 thin films in MFS structure determined by DLTS and C – V technique

BaTiO3 and Ba0.9Ca0.1TiO3 thin films were deposited on the p – type Si substrate by pulsed excimer laser ablation technique. The Capacitance – Voltage (C-V) measurement measured at 1 MHz exhibited a clockwise rotating hysteresis loop with a wide memory window for the Metal – Ferroelectric – Semiconductor (MFS) capacitor confirming the ferroelectric nature. The low frequency C – V measurements exhibited the response of the minority carriers in the inversion region while at 1 MHz the C – V is of a high frequency type with minimum capacitance in the inversion region. The interface states of both the MFS structures were calculated from the Castagne – Vaipaille method (High – low frequency C – V curve). Deep Level Transient Spectroscopy (DLTS) was used to analyze the interface traps and capture cross section present in the MFS capacitor. There were distinct peaks present in the DLTS spectrum and these peaks were attributed to the presence of the discrete interface states present at the semiconductor – ferroelectric interface. The distribution of calculated interface states were mapped with the silicon energy band gap for both the undoped and Ca doped BaTiO3 thin films using both the C – V and DLTS method. The interface states of the Ca doped BaTiO3 thin films were found to be higher than the pure BaTiO3 thin films.

Alloy oxide equilibria in the system Ca Al O at 1373 K

The tie lines delineating equilibria between different oxides of the Ca-Al-O system and liquid Ca-Al alloy has been determined at 1373 K. Equilibration of the alloy with two adjacent oxide phases in the CaO-Al2O3 pseudo-binary system was established in a closed cell made of iron. Equilibrium oxide phases were confirmed by x-ray analysis and alloy compositions were determined by chemical analysis. The compound 12CaO.7Al2O3 Ca12Al14O33 was found to be a stable phase in equilibrium with calcium alloys. The experimental diagram is consistent with that calculated from the free energies of formation of the oxide phases and activities in liquid Ca-Al alloys at 1373 K reported in the literature.

Colloidal calcium nanoparticles: digestive ripening in the presence of a capping agent and coalescence of particles under an electron beam

The nanochemistry of calcium remains unexplored, which is largely due to the inaccessibility of calcium nanoparticles in an easy to handle form by conventional methods of synthesis as well as its highly reactive and pyrophoric nature. The synthesis of colloidal Ca nanoparticles by the solvated metal atom dispersion (SMAD) method is described. The as-prepared Ca-THF nanoparticles, which are polydisperse, undergo digestive ripening in the presence of a capping agent, hexadecyl amine (HDA) to afford highly monodisperse colloids consisting of 2-3 nm sized Ca-HDA nanoparticles. These are quite stable towards precipitation for long periods of time, thereby providing access to the study of the nanochemistry of Ca. Particles synthesized in this manner were characterized by UV-visible spectroscopy, high resolution electron microscopy, and powder X-ray diffraction methods. Under an electron beam, two adjacent Ca nanoparticles undergo coalescence to form a larger particle.