Studies on the ionic transport and structural investigations of La0.5Li0.5TiO3 perovskite synthesized by wet chemical methods and the effect of Ce, Zr substitution at Ti site

La0.5Li0.5TiO3 perovskite was synthesized by various wet chemical methods. By adopting low temperature methods of preparation lithium loss from the material is prevented. La0.5Li0.5TiO3 (LLTO) was formed with cubic symmetry at 1473 K. LLTO was formed at relatively lower temperature by using hydrothermal preparation method. PVA gel-decomposition route yield tetragonal LLTO on annealing the dried gel at 1473 K. By using gel-carbonate route LiTi2O4 minor phase was found to remain even after heat-treatment at 1473 K. The hydroxylation of LLTO was done in deionized water as well as in dilute acetic acid medium. By hydroxylation process incorporation of hydroxyls and leaching out of Li+ was observed from the material. The Li+ concentration of these compositions was examined by AAS. The electrical conductivities of these compositions were measured by dc and ac impedance techniques at elevated temperatures. The activation energies of electrical conduction for these compositions were estimated from the experimental results. The measured activation energy of Li+ conduction is 0.34 eV. Unhydroxylated samples exhibit only Li+ conduction, whereas, the hydroxylated LLTO show proton conductivity at 298-550 K in addition to Li+ conductivity. The effect of Zr or Ce substitution in place of Ti were attempted. La0.5Li0.5ZrO3 Perovskite was not formed; instead pyrochlore phase (La2Zr2O7) along with monoclinic ZrO2 phases was observed above 1173 K; below 1173 K cubic ZrO2 is stable. (La0.5Li0.5)(2)CeO4 solid solution was formed in the case of Ce substitution at Ti sublattice on heat-treatment up to 1673 K. (c) 2005 Springer Science + Business Media, Inc.

Mechanism of low-temperature deformation in quenched aluminium-magnesium alloys

The dislocation mechanisms for plastic flow in quenched AlMg alloys with 0.45, 0.9, 2.7 and 6.4 at. % Mg were investigated using tensile tests and change-in-stress creep experiments in the temperaturhttp://eprints.iisc.ernet.in/cgi/users/home?screen=EPrint::Edit&eprintid=28109&stage=core#te range 87° -473° K. The higher the magnesium content in the alloy, the higher was the temperature dependence of flow stress. The alloys showed no perceptible creep in the vicinity of room temperature, while they crept at lower as well as higher temperatures. The most probable cause of hardening at temperatures below ∼ 200° K was found to be the pinning of dislocations by randomly distributed solute atoms, while athermal locking of dislocations by dynamic strain ageing during creep was responsible for the negligibly small creep rate in the room temperature range.

Preparation of lower oxide of sulphur

RECENT work on the lower oxide of sulphur1,2 has established that disulphur monoxide (S2O) or its polymeric form is produced when sulphur is burnt in oxygen under reduced pressure. It has now been shown that it is possible to make use of an oxide of a heavy metal as a source of limited supply of oxygen to prepare the disulphur monoxide. For example, when a mixture of finely powdered cupric oxide and sulphur (1 : 5 by weight) is heated under vacuum in a glass tube gaseous products are evolved. which, on cooling in a trap surrounded by liquid air, will give an orange-red condensate (S2O)x. This condensate also gives off sulphur dioxide in stages as the temperature is raised, finally leaving a residue of elemental sulphur. Copper sulphide and excess of sulphur are left behind in the reaction tube.

The effect of temperature on the magnetic susceptibility of vanadium pentoxide systems

The magnetic susceptibilities of certain vanadium pentoxide systems supported by kieselgur have been determined in the temperature interval 30° to 400° C. The plot of reciprocal susceptibility against temperature for all the systems studied indicates sudden deflections at temperatures which are about 150° lower than those of optimum catalytic activity. It has been suggested that these points may mark the temperatures of commencement of structural changes which may be responsible for the activity of these catalysts.

Effect of disorder on the exponent in the coherence region in high temperature superconductors

Effect of disorder on the electrical resistance near the superconducting transition temperature in the paracoherence region of high temperature YBa2CU3O7-delta (YBCO) thin film superconductor is reported. For this, c-axis oriented YBa2Cu3O7-delta thin films having superconducting transition width varying between 0.27 K and 6 K were deposited using laser ablation and high pressure oxygen sputtering techniques. Disorder in these films was further created by using 100 MeV oxygen and 200 MeV silver ions with varying fluences. It is observed that the critical exponent in the paracoherence region for films with high transition temperature and small transition width is in agreement with the theoretically predicted value (gamma = 1.33) and is not affected by disorder, while for films with lower transition temperature and larger transition width the value of exponent is much larger as compared to that theoretically predicted and it varies from sample to sample and usually changes with disorder induced by radiation. This difference in the behaviour of the exponent has been explained on the basis of differences in the strength of weak links and the transition between temperatures T. and T, is interpreted as a percolation like transition with disorder. (c) 2006 Elsevier B.V. All rights reserved.

Dielectric relaxation and electrical conductivity in Bi5NbO10 oxygen ion conductors prepared by a modified sol–gel process

Crystalline Bi5NbO10 nanoparticles have been achieved through a modified sol–gel process using a mixture of ethylenediamine and ethanolamine as a solvent. The Bi5NbO10 nanoparticles were characterized by X-ray diffraction (XRD), differential scanning calorimetry/thermogravimetry (DSC/TG), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and Raman spectroscopy. The results showed that well-dispersed 5–60 nm Bi5NbO10 nanoparticles were prepared through heat-treating the precursor at 650 °C and the high density pellets were obtained at temperatures lower than those commonly employed. The frequency and temperature dependence of the dielectric constant and the electrical conductivity of the Bi5NbO10 solid solutions were investigated in the 0.1 Hz to 1 MHz frequency range. Two distinct relaxation mechanisms were observed in the plots of dielectric loss and the imaginary part of impedance (Z″) versus frequency in the temperature range of 200–350 °C. The dielectric constant and the loss in the low frequency regime were electrode dependent. The ionic conductivity of Bi5NbO10 solid solutions at 700 °C is 2.86 Ω−1 m−1 which is in same order of magnitude for Y2O3-stabilized ZrO2 ceramics at same temperature. These results suggest that Bi5NbO10 is a promising material for an oxygen ion conductor.

Polarization switching in near-stoichiometric Zn:LiNbO3 at high temperatures

The effect of temperature and stoichiometry on the polarization switching rate in lithium niobate is presented. An increased polarization switching rate in congruent and near-stoichiometric lithium niobate (CLN and SLN) and SLN doped with 1.6 mol% Zn (SLN:Zn(1.6)) is observed using a pulsed field switching technique near the transition temperature (TO. Compared to CLN, the observed switching rate and domain wall mobility for SLN and SLN:Zn(1.6) are higher. The extra charge flow was observed during switching at high temperatures,and is attributed to the creation of defect dipoles and increase in ionic conductivity. Forward domain motion is expected to be the mechanism involved in switching. (C) 2010 Elsevier Ltd. All rights reserved.

Time-dependent analysis of an N2O gasdynamic laser

A simplified two-temperature model is presented for the vibrational energy levels of the N2O and N2 molecules of an N2O-N2-He gasdynamic laser (GDL), and the governing equations for the unsteady flow of the gas mixture in a convergent-divergent contour nozzle are solved using a time-dependent numerical technique. Final steady-state distributions are obtained for vibrational temperatures, population inversion, and the small-signal laser gain along the nozzle. It is demonstrated that, for plenum temperatures lower than 1200 K, an N2O GDL such as the present is more efficient than a CO2 GDL in identical operating conditions

Bearing capacity of interfering multiple strip footings by using lower bound finite elements limit analysis

The ultimate bearing capacity of a number of multiple strip footings, identically spaced and equally loaded to failure at the same time,is computed by using the lower bound limit analysis in combination with finite elements. The efficiency factor due to the component of soil unit weight, is computed with respect to changes in the clear spacing (xi(gamma)) between the footings. It is noted that the failure load for a footing in the group becomes always greater than that of a single isolated footing. The values of xi(gamma) for the smooth footings are found to be always lower than the rough footings. The values ofxi(gamma) are found to increase continuously with a decrease in the spacing between footings. As compared to the available theoretical and experimental results reported in literature, the present analysis provides generally a little lower values of xi(gamma). (C) 2010 Elsevier Ltd. All rights reserved.

Role of hydroxyl group on the mesomorphism of alkyl glycosides:synthesis and thermal behavior of alkyl 6-deoxy-beta-D-glucopyranosides

A homologous series of alkyl 6-deoxy-beta-D-glucopyranoside amphiphiles was prepared,in an effort to identify the role of hydroxyl group in the mesomorphic behavior of alkyl glycosides. Synthesis was performed by a chlorination of the sugar moiety in alkyl-beta-D-glucopyranosides with methylsulfonyl chloride in DMF, followed by a metal mediated dehalogenation to secure alkyl 6-deoxy-beta-D-glucopyranosides, wherein the alkyl chain length varied from C-9 to C-16. The mesomorphic behavior of these 6-deoxy alkyl glycosides was assessed using polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction method. Whereas the lower homologues exhibited a monotropic SmA phase till sub-ambient temperatures, the higher homologues formed a plastic phase. A partial interdigitized bilaye structure of SmA phase is inferred from experimental d-spacing and computationally derived lengths of the molecules. The results were compared with those of normal alkyl glucopyranosides, retained with hydroxyl groups at C-2-C-6 carbons, and alkyl 2-deoxy-glucopyranosides, devoid of a hydroxyl group at C-2 and the comparison showed important differences in the mesomorphic behavior.(C)2010 Elsevier Ireland Ltd. All rights reserved.

Triangular Ising antiferromagnet in a staggered field

We study the equilibrium properties of the nearest-neighbor Ising antiferromagnet on a triangular lattice in the presence of a staggered field conjugate to one of the degenerate ground states. Using a mapping of the ground states of the model without the staggered field to dimer coverings on the dual lattice, we classify the ground states into sectors specified by the number of "strings." We show that the effect of the staggered field is to generate long-range interactions between strings. In the limiting case of the antiferromagnetic coupling constant J becoming infinitely large, we prove the existence of a phase transition in this system and obtain a finite lower bound for the transition temperature. For finite J, we study the equilibrium properties of the system using Monte Carlo simulations with three different dynamics. We find that in all the three cases, equilibration times for low-field values increase rapidly with system size at low temperatures. Due to this difficulty in equilibrating sufficiently large systems at low temperatures, our finite-size scaling analysis of the numerical results does not permit a definite conclusion about the existence of st phase transition for finite values of J. A surprising feature in the system is the fact that unlike usual glassy systems; a zero-temperature quench almost always leads to the ground state, while a slow cooling does not.

Exact solution for the unsteady flow and heat transfer between eccentrically rotating disks

The unsteady heat transfer associated with flow due to eccentrically rotating disks considered by Ramachandra Rao and Kasiviswanathan (1987) is studied via reformulation in terms of cylindrical polar coordinates. The corresponding exact solution of the energy equation is presented when the upper and lower disks are subjected to steady and unsteady temperatures. For an unsteady flow with nonzero mean, the energy equation can be solved by prescribing the temperature on the disk as a sum of steady and oscillatory parts