Synthesis, structural and ferromagnetic properties of La1-xKxMnO3 (0.0 <= x <= 0.25) phases by solution combustion method

We describe the solution combustion synthesis and characterization of La1-xKxMnO3 (0.0 <= x <= 0.25) perovskite phases, which is a low temperature initiated, rapid route to prepare metal oxides. As-synthesized compounds are amorphous in nature; crystallinity was observed on heating at 800 degrees C for 5 min. Structural parameters were determined by the Rietveld refinement method using powder XRD data. Parent LaMnO3 compound crystallizes in the orthorhombic structure (space group Pbnm, No. 62). Potassium substituted compounds were crystallized with rhombohedral symmetry (space group R-3c, No. 167). The ratio of the Mn3+/Mn4+ was determined by the iodometric titration. The Fourier transform infrared spectrum (FTIR) shows two absorption bands for Mn-O stretching vibration (v, mode), Mn-O-Mn deformation vibration (v(b) mode) around 600 cm(-1) and 400 cm(-1) for the compositions, x = 0.0, 0.05 and 0-10. Four-probe electrical resistivity measurements reveal a composition controlled metal to insulator transition (TM-1), the maximum TM-1 was observed for the composition La0.85K0.15MnO3 at 287 K. Room temperature vibrating sample magnetometer data indicate that for the composition up to x = 0-10, the compounds are paramagnetic whereas composition with x = 0.15, 0.20 and 0.25 show magnetic moments of 27, 29 and 30 emu/g, respectively.

Mixed mode (I and II) crack tip fields in bulk metallic glasses

Stationary crack tip fields in bulk metallic glasses under mixed mode (I and II) loading are studied through detailed finite element simulations assuming plane strain, small scale yielding conditions. The influence of internal friction or pressure sensitivity on the plastic zones. notch deformation, stress and plastic strain fields is examined for different mode mixities. Under mixed mode loading, the notch deforms into a shape such that one part of its surface sharpens while the other part blunts. Increase in mode If component of loading dramatically enhances the normalized plastic zone size, lowers the stresses but significantly elevates the plastic strain levels near the notch tip. Higher internal friction reduces the peak tangential stress but increases the plastic strain and stretching near the blunted part of the notch. The simulated shear bands are straight and extend over a long distance ahead of the notch tip under mode II dominant loading. The possible variations of fracture toughness with mode mixity corresponding to failure by brittle micro-cracking and ductile shear banding are predicted employing two simple fracture criteria. The salient results from finite element simulations are validated by comparison with those from mixed mode (I and II) fracture experiments on a Zr-based bulk metallic glass.

Possible mechanism of charge transport and dielectric relaxation in SrO-Bi2O3-B2O3 glasses

Transparent SrBi2B2O7 glasses were prepared via melt-quenching technique and characterized using differential scanning calorimetry and x-ray powder diffraction. The ac conductivities of the glasses were studied as a function of frequency (100 Hz-10 MHz) at different temperatures. The frequency dependence of conductivity has been analyzed using Almond-West expression. The exponent n was nearly unaffected by temperature. Impedance and modulus spectroscopies were employed to further examine the electrical data. Dielectric relaxation exhibited a stretched exponential behavior with a stretching exponent beta independent of temperature. From conductivity analysis we have proposed that the charge transport occurs through the participation of nonbridging oxygen (NBO), which switches positions in a facile manner. The stretched exponential behavior appears to be a direct consequence of the NBO switching mechanism of charge transport.

Simulation of laminar flow in a three-dimensional lid-driven cavity by lattice Boltzmann method

Purpose - The purpose of this paper is to apply lattice Boltzmann equation method (LBM) with multiple relaxation time (MRT) model, to investigate lid-driven flow in a three-dimensional (3D), rectangular cavity, and compare the results with flow in an equivalent two-dimensional (2D) cavity. Design/methodology/approach - The second-order MRT model is implemented in a 3D LBM code. The flow structure in cavities of different aspect ratios (0.25-4) and Reynolds numbers (0.01-1000) is investigated. The LBM simulation results are compared with those from numerical solution of Navier-Stokes (NS) equations and with available experimental data. Findings - The 3D simulations demonstrate that 2D models may predict the flow structure reasonably well at low Reynolds numbers, but significant differences with experimental data appear at high Reynolds numbers. Such discrepancy between 2D and 3D results are attributed to the effect of boundary layers near the side-walls in transverse direction (in 3D), due to which the vorticity in the core-region is weakened in general. Secondly, owing to the vortex stretching effect present in 3D flow, the vorticity in the transverse plane intensifies whereas that in the lateral plane decays, with increase in Reynolds number. However, on the symmetry-plane, the flow structure variation with respect to cavity aspect ratio is found to be qualitatively consistent with results of 2D simulations. Secondary flow vortices whose axis is in the direction of the lid-motion are observed; these are weak at low. Reynolds numbers, but become quite strong at high Reynolds numbers. Originality/value - The findings will be useful in the study of variety of enclosed fluid flows.

High-pressure Raman and infrared spectroscopic studies of ZrP2O7

High-pressure Raman and mid-infrared spectroscopic studies were carried out on ZrP2O7 to 23.2 and 13 GPa respectively. In the pressure range 0.7-4.3 GPa the lattice mode at 248 cm(-1) disappears, new modes appear around 380 and 1111 cm(-1) and the strong symmetric stretching mode at 476 cm(-1) softens, possibly indicating a subtle phase transition. Above 8 GPa all the modes broaden, and all of the Raman modes disappear beyond 18 GPa. On decompression from the highest pressure, 23.2, to 0 GPa all of the modes reappear but with larger full width at half maximum. Lattice dynamics of the high temperature phase of ZrP2O7 were studied using first principles method and compared with experimental values. (C) 2009 Elsevier Ltd. All rights reserved.

Photocatalytic degradation of methyl methacrylate copolymers

The photolytic and photocatalytic degradation of the copolymers poly(methyl methacrylate-co-butyl methacrylate) (MMA–BMA), poly(methyl methacrylate-co-ethyl acrylate) (MMA–EA) and poly(methyl methacrylate-co-methacrylic acid) (MMA–MAA) have been carried out in solution in the presence of solution combustion synthesized TiO2 (CS TiO2) and commercial Degussa P-25 TiO2 (DP 25). The degradation rates of the copolymers were compared with the respective homopolymers. The copolymers and the homopolymers degraded randomly along the chain. The degradation rate was determined using continuous distribution kinetics. For all the polymers, CS TiO2 exhibited superior photo-activity compared to the uncatalysed and DP 25 systems, owing to its high surface hydroxyl content and high specific surface area. The time evolution of the hydroxyl and hydroperoxide stretching vibration in the Fourier transform-infrared (FT-IR) spectra of the copolymers indicated that the degradation rate follows the order MMA–MAA > MMA–EA > MMA–BMA. The same order is observed for the rate coefficients of photocatalytic degradation. The photodegradation rate coefficients were compared with the activation energy of pyrolytic degradation. In degradation by pyrolysis, it was observed that MMA–BMA was the least stable followed by MMA–EA and MMA–MAA. The observed contrast in the order of thermal stability compared to the photo-stability of these copolymers was attributed to the two different mechanisms governing the scission of the polymer and the evolution of the products.

Hydrothermal synthesis and characterization of CaSO4 pseudomicrorods

Calcium sulphate (CaSO4) pseudomicrorods have been synthesized by alow-temperature hydrothermal method using CaSO4 powder as a precursor and hexadecylamine as a surfactant at 180 degrees C for at different intervals of time. The powder X-ray diffraction pattern indicates that the as-formed pseudomicrorods are of orthorhombic phase with lattice parameters a = 7.0023(4) angstrom, b = 6.9939(5) angstrom and c = 6.2434(4) angstrom. Scanning electron microscopy images show that the pseudomicrorods have diameters of about 0.2-2.5 mm and lengths of about 2-10 mm. Fourier transform infrared spectroscopy shows a strong doublet near 609 and 681 cm(-1) arising from nu(4) (SO42) bending vibrations. The strongest band observed at 1132 cm(-1) is associated with nu(3) (SO42-) stretching vibrations. The band near 420-450 cm(-1) is attributed to nu(2) (SO42-) bending vibrations. The Raman spectrum exhibits an intense peak at 1008 cm(-1) associated with the SO42- mode. The photoluminescence spectrum exhibits UV bands (330, 350 nm), strong green bands (402, 436 nm) and weak blue bands (503 nm). A widening of the optical band gap was observed as the particle size decreased.

Infrared absorption spectra of single crystals of glycine silver nitrate and monoglycine nitrate

he infrared absorption spectra of glycine silver nitrate (GAgNO3) and glycine nitrate (GHNO3) show that the glycine group exists completely in the zwitter ion form in the former and in both forms in the latter. The spectrum of GAgNO3 at liquid air temperature did not reveal any striking change which can be attributed to a freezing of the rapid reorientation of the NH3+ group taking place at higher temperatures. The position of the COO− stretching frequencies indicate that this group is co-ordinated only weakly to the Ag+ ion. The summation frequencies reported by Schroeder, Wier and Lippincott (1962) for AgNO3 were not observed in the present study on GAgNO3. It shows however that ferroelectricity in GAgNO3 is in all probability due to the motion of the Ag+ ion in the oxygen co-ordination polyhedron and is not directly connected with the ordering of the hydrogen bonds below Curie point.

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.

Infrared spectrum of ferroelectric lithium hydrazinium sulphate [Li (N2H5) SO4]

Dielectric observations on lithium hydrazinium sulphate have shown earlier that it is ferroelectric over a range of temperatures from below −15° C. to above 80° C. and a new type of hydrogen bond rearrangement which would allow the protons to migrate along the chain has also been suggested by others. The infrared spectrum of LiH z S in the form of mull and as single crystal sections parallel and perpendicular to the ‘C’ axis exhibit about 21 well-defined absorption maxima. The position and the width of the maxima agree with the known structure of the crystal according to which the hydrazine group exists in the form of the hydrazinium ion, NH2·NH3+ and the observed N+-H frequencies agree better with the new correlation curve given by R. S. Krishnan and K. Krishnan (1964). However it has been pointed out that from a comparative study of the new infrared spectra of hydrazonium sulphate and lithium ammonium sulphate that the absorption band at 969 cm.−1 is due to N-N stretching vibration and that the fairly intense band between 2050–2170 cm.−1 is due to the bending vibrations of the NH3+ group.

Infra-red and raman spectra of BaCl2.2H2O and BaCl2.2D2O

The infra-red and Raman spectra of ordinary and deuterated barium chloride dihydrate have been studied to throw light on the intramolecular hydrogen bonds in these two crystals. The frequencies of the stretching, bending and librational modes observed in infra-red and Raman spectra exclude the possibility of at least one of the OH.... Cl hydrogen bonds, contrary to the results of NMR and neutron diffraction studies.

Raman spectrum of crystalline aminosulphonic acid

The Raman spectrum of a single crystal of sulphamic acid has been recorded withλ 2537 excitation. Thirty-eight lines have been observed, of which twenty-nine have been recorded for the first time. Seven Raman lines with shifts in the region 50–155 cm.−1 have been assigned to the lattice oscillations, two at 177 and 240 cm.−1 have been attributed to the low-frequency hydrogen bond vibrations.. The splitting of the degenerate modes and the appearance of N-H....O bonded stretching vibrations are consistent with the structural data which expect the presence of the free molecule as a Zwitter ion with only slight distortion from C3v symmetry.

Raman spectra of ferro-electric crystals Part IV. Lithium hydrazinium sulphate (LiN2H5SO4)

The Raman spectrum of lithium hydrazinium sulphate has been recorded both in the single crystal form and in aqueous solutions. The crystal exhibits thirty-eight Raman lines having the frequency shifts 52, 70, 104, 146, 174, 220, 260, 302, 350, 454, 470, 610, 630, 715, 977, 1094, 1115, 1132, 1177, 1191, 1260, 1444, 1493, 1577, 1630, 1670, 2205, 2484, 2553, 2655, 2734, 2848, 2894, 2939, 3028, 3132, 3290 and 3330 cm.−1 The aqueous solution gave rise to six Raman lines at 452, 980, 1050–1200, 1260, 1425 and 1570 cm.−1 apart from a maximum at 180 cm.−1 in the ‘wing’ accompanying the Rayleigh line. The observed Raman lines have been assigned as arising from the vibrations of the SO4 ion, N2H5+ ion, Li-O4 group, hydrogen bond and the lattice. The influence of the hydrogen bond on the N-H stretching vibrations has been pointed out. The various features of the observed spectrum strongly support the hypothesis that the NH3 group in the crystal is rotating around the N-N axis at room temperature.

Raman spectrum of guanidinium aluminium sulphate hexahydrate

The Raman spectrum of guanidinium aluminium sulphate hexahydrate also known as ‘GASH’ which is a ferro-electric crystal and has strong hydrogen bonds has been recorded. 38 Raman lines have been identified in the spectra of GASH. The O-H stretching mode is found to be very much influenced by the hydrogen bond and they appear over a widely extended region from 2240–3600 cm.−1 It can therefore be concluded that all the O-H bonds are hydrogen bonded and some of them are quite strong. The Raman lines due to the N-H vibrations appear with the normal frequency shifts indicating thereby that N-H bonds are not hydrogen bonded. These conclusions are fully supported by the results obtained from the X-ray crystal structure analysis of GASH. The principal vibrations of the Al-(OH2)6 groups have also been identified.

Raman spectrum of hydroxylamine hydrochloride (NH3OH.Cl)

The Raman spectrum of hydroxylamine hydrochloride (NH3OH.Cl) in the form of a single crystal has been photographed usingλ 2536·5 excitation. 32 Raman lines with frequency shifts 40, 57, 78, 88, 111, 125, 135, 156, 187, 217, 250, 330, 550, 575, 1004, 1168, 1204, 1470, 1496, 1565, 1590, 1979, 2636, 2710, 2750, 2789, 2926, 2970, 3000, 3050, 3141 and 3220 cm.−1 have been recorded. Of these, the first 8 low-frequency lines belong to the external oscillation, while the four lines at 187, 217, 250 and 330 cm.−1 should be attributed to the vibrations of the hydrogen bond valence vibrations. The remaining Raman lines have been assigned to the vibrations of the NH3OH ion. The O-H and N-H stretching vibrations are very much influenced by the presence of the hydrogen bonds in the crystal.