Wet chemical formation of nanoparticles of binary perovskites through isothermal gel to crystallite conversion

Coarse BO2·xH2O (2 < x < 80) gels, free of anion contaminants react with A(OH)2 under refluxing conditions at 70�100°C giving rise to crystallites of single phased, nanometer size powders of ABO3 perovskites (A = Ba, Sr, Ca, Mg, Pb; B = Zr, Ti, Sn). Solid solutions of perovskites could be prepared from compositionally modified gels or mixtures of A(OH)2. Donor doped perovskites could also be prepared from the same method so that the products after processing are often semiconducting. Faster interfacial diffusion of A2+ ions into the gel generates the crystalline regions whose composition is controllable by the A/B ratio as well as the A(OH)2 concentration.

Mott insulator high T-c bipolaronic superconductor transition in cuprates - Discussion

All ‘undoped’ cuprates are antiferromagnetic Mott insulators. We argue that with doping they remain to be insulators including the ‘overdoped’ samples. Hence, there is no clear dividing line between non–metallic cuprates and high–temperature superconductors. Based on the generic Hamiltonian including the electron–phonon interaction and the direct Coulomb repulsion the ground state of doped cuprates is shown to be a charged 2e Bose liquid of small bipolarons. A theory of the normal state transport of copper oxides is developed. The temperature dependence of the resistivity and of the Hall effect agrees remarkably well with the experimental data in La2–xSrxCuO4 for the entire temperature regime including unusual ‘logarithmic’ low–temperature region. The violation of Kohler's rule in magnetoresistivity is explained. The resistive and thermodynamic superconducting transitions in a magnetic field are quantitatively described.

Deformation behaviour of commercially pure titanium at extreme strain rates

The evolution of microstructure and texture during room temperature compression of commercially pure Ti with four different initial orientations were studied under quasi-static and dynamic loading conditions. At a low strain rate (epsilon)over dot = 3 x 10(-4) s(-1) the different initial textures yielded the same end texture, despite different microstructural evolution in terms of twin boundaries. High strain rate deformation at (epsilon)over dot = 1.5 x 10(3) s(-1) was characterized by extensive twinning and evolution of a texture that was similar to that at low strain rate with minor differences. However, there was a significant difference in the strength of the texture for different orientations that was absent for low strain rate deformed samples at high strain rate. A viscoplastic self-consistent model with a secant approach was used to corroborate the experimental results by simulation. (C) 2011 Published by Elsevier Ltd. on behalf of Acta Materialia Inc.

Influence of growth below and above T-c on the morphology and domain structure in flux-grown KTP crystals

KTP crystals have been grown below and above the ferroelectric transition temperature by flux method employing both spontaneous and top-seeded solution growth techniques. A slight morphological difference has been observed in these crystals when grown below and above the T-c. Ferroelectric domains are studied in these crystals by selective domain etching. It is seen that the ferroelectric domains in crystals grown spontaneously below T, show a complicated structure. A systematic investigation of the factors influencing domain structure has been carried out. Stress to some extent has been shown to affect the domain structure. Finally, a convenient way of converting the multidomain crystals into monodomain ones is described.

Enantioselective total synthesis of iso-cladospolide B, cladospolide C and cladospolide B from tartaric acid

The enantioselective synthesis of the natural products cladospolide B, cladospolide C, and iso-cladospolide B has been accomplished from tartaric acid. Key reactions in the synthetic sequence include the elaboration of a gamma-hydroxy amide derived from tartaric acid via alkene cross metathesis, Yamaguchi lactonization, and ring closing metathesis. (C) 2011 Elsevier Ltd. All rights reserved.

Structural and conformational study of peptides containing glycine and alanine residues by C-13 CPMAS NMR spectroscopy in solid state

The results of the structural and conformational studies carried out using C-13 CPMAS NMR technique on several glycine and alanine containing peptides in the solid state are reported. The study demonstrates the effects of variations in C-13 chemical shifts due to conformation and hydrogen bonding. The possibility of applying this technique to obtain insight into the conformational characteristics of peptides of unknown structures is discussed.

Studies on multi-metal ion tolerance of Thiobacillus ferrooxidans

The influence of different concentrations of base metal ions, such as CU2+, Zn2+ and Fe3+, when present either alone or in different possible binary and ternary combinations in a 9K medium, on the fel rous ion oxidation ability of Thiobacillus ferrooxidans was studied. Levels and degree of toxicity of these ions have been quantified in terms of toxicity index (TI). Copper and zinc tolerant strains of the bacteria were developed through serial subculturing and their activity tested in the presence of the above metal ions in comparison with the behavior of wild unadapted cells under similar conditions. Copper tolerant strains (25 g/L Cu2+) were found to be more efficient in the bioleaching of both copper and zinc concentrates than wild unadapted strains, while zinc tolerant strains (40 g/L Zn2+) exhibited better leaching efficiency only in the bioleaching of sphalerite concentrates. The significance and relevance of multi-metal ion tolerance in Thiobacillus ferrooxidans has been highlighted with respect to bioleaching of sulphide mineral concentrates. (C) 1997 Published by Elsevier Science Ltd.

Synthesis of Ti, Ga, and V nitrides: Microwave-assisted carbothermal reduction and nitridation

A simple, novel, and fast method of preparation of metal nitride powders (GaN, TiN, and VN) using microwave-assisted carbothermal reduction and nitridation has been demonstrated. The procedure uses the respective oxides and amorphous carbon powder as the starting materials. Ammonia gas is found to be more effective in nitridation than high-purity N-2 gas. Complete nitridation is achieved by the use of a slight excess of amorphous carbon. Metals themselves are not found to be effectively nitrided. The products were characterized using XRD, TEM, and SAED and found to possess good crystallinity and phase purity. The method can be of general applicability for the preparation of metal nitrides.

Unstable flow during hot deformation of Ti-24Al-20Nb alloy

Unstable flow during hot deformation of an alpha(2) titanium aluminide alloy Ti-24Al-20Nb alloy was analysed using two criteria, one of which was developed by Jonas and the other by Kalyankumar. Workability maps were constructed using the alpha parameter as suggested by Semiatin and Lahoti and instability maps were constructed based on the stability parameter xi(epsilon) as suggested by Kalyankumar. Microstructural study was carried out on deformed specimens to validate the two criteria. The results of the two criteria were compared. The particular case of highly negative alpha values has been discussed in detail and it is shown that these correspond to regions of unstable flow.

Muon-spin rotation spectra in the mixed phase of high-T-c superconductors: Thermal fluctuations and disorder effects

We study muon-spin rotation (mu SR) spectra in the mixed phase of highly anisotropic layered superconductors, specifically Bi2+xSr2-xCaCu2O8+delta (BSCCO), by modeling the fluid and solid phases of pancake Vortices using liquid-state and density functional methods. The role of thermal fluctuations in causing motional narrowing of mu SR line shapes is quantified in terms of a first-principles theory of the flux-lattice melting transition. The effects of random point pinning are investigated using a replica treatment of liquid-state correlations and a replicated density functional theory. Our results indicate that motional narrowing in the pure system, although substantial, cannot account for the remarkably small linewidths obtained experimentally at relatively high fields and low temperatures. We find that satisfactory agreement with the mu SR data for BSCCO in this regime can be obtained through the ansatz that this ''phase'' is characterized by frozen short-range positional correlations reflecting the structure of the liquid just above the melting transition. This proposal is consistent with recent suggestions of a ''pinned liquid'' or ''glassy'' state of pancake Vortices in the presence of pinning disorder. Our results for the high-temperature liquid phase indicate that measurable linewidths may be obtained in this phase as a consequence of density inhomogeneities induced by the pinning disorder. The results presented here comprise a unified, first-principles theoretical treatment of mu SR spectra in highly anisotropic layered superconductors in terms of a controlled set of approximations. [S0163-1829(99)08033-9].

New lithium-ion conductors based on the NASICON structure

Lithium-ion conduction in mixed-metal phosphates, (LiMMIII)-M-V(PO,), [M-V = Nb, Ta; M-III = Al, Cr, Fe], possessing the rhombohedral (R (3) over bar c) NASICON structure has been investigated. Among the phosphates investigated, LiTaAl(PO4)(3) exhibits the highest conductivity, sigma approximate to 1.0 x 10(-2) S cm(-1) at 350 degrees C (E-a = 0.47 eV), comparable to the conductivity of LiTi2(PO4)(3). Unlike LiTi2(PO4)(3) which contains lithium-reducible Ti-IV, LiTaAl(PO4)(3) contains stable Ta-V and Al-III oxidation states and hence deserves further attention towards tailoring new lithium-ion conductors for application as electrolytes in solid state lithium batteries.

Phase transitions in triammonium hydrogen disulphate: Crystal structure of an intermediate stable phase at-90 degrees C

Triammonium hydrogen disulphate, (NH4)(3)H(SO4)(2), belongs to the family of crystal structures M3H(XO4)(2) (with M = NH4, K, Rb, Cs, and X = S, Se) which display super protonic phases at elevated temperatures, while at room temperature these are relatively poor proton conductors. The crystal structure of triammonium hydrogen disulphate has been determined by X-ray diffraction at -90 degrees C and the variation in the characteristics of the hydrogen bond is discussed in comparison with that of the structures at -110 degrees C and room temperature. It is concluded that the mechanics involving the proton migration in such systems is realised in terms of the variations in the hydrogen bond features with temperature.

Role of oxygen transients in the facile scission of C-O bonds of alcohols on Zn surfaces

The alkoxy species produced by the interaction of alcohols with Zn surfaces undergoes C-O bond scission at 150 K giving hydrocarbon species, but this transformation occurs even at 80 K when alcohol-oxygen mixtures are coadsorbed, due to the oxygen transients.

Synthesis and structure of a novel terminal imido complex of titanium

The reaction of eta(5)-Cp*TiCl3 and (LiNHBu)-Bu-t in hexanes yields a novel [eta(5)-Cp*Ti(=(NBu)-Bu-t)((NHBu)-Bu-t)(2)]Li . (NH2Bu)-Bu-t complex with a terminal tert-butylimido moiety. The synthesis and X-ray structural characterization are described. (C) 1999 Elsevier Science S.A. All rights reserved.

Synthesis of mesoporous materials based on titanium(IV)oxide and titanium nitride

Nanoparticles of titania were obtained by the controlled hydrolysis of Ti(i-OC3H7)(4) in the reverse micelles of dodecylamine derived from dodecylamine-isopropanol-water solution (water/oil microemulsion). The mesolamellar phase based on titanium nitride (TiN) was obtained by first decomposing TiN atleast partially using the 1:1 solution of acid mixture (HF and HNO3 in the ratio of 9:1) in water and then templating onto the cationic surfactant namely, cetyltrimethylammaniumbromide (abbreviated as CTAB) at 80 degrees C. The synthesis of mesolamellar phase based on TiN involves the charge matched templating approach following the counter-ion mediated pathway. The samples thus obtained were characterized by small angle x-ray diffraction using Cuk(a) radiation, scanning electron microscopy and transmission electron microscopy, which indicated some satisfactory results. (C) 1999 Acta Metallurgica Inc.