Elastic properties and spectroscopic studies of fast ion conducting Li2O-ZnO-B2O3 glass system

Glass systems of the composition xLi(2)O-20ZnO-(80 - x)B2O3 where (x = 5, 10, 15, 20, 25 and 30 mol%) have been prepared by melt quenching technique. Elastic properties, 1 B-11 MAS-NMR and IR spectroscopic studies have been employed to study the structure of Li2O-ZnO-B2O3 glasses. Elastic properties have been investigated using sound velocity measurements at 10 MHz. Elastic moduli reveal trends in their compositional dependence. The bulk modulus and shear modulus increases monotonically with increase of BO4 units, which increase the dimensionality of the network. B-11 MAS-NMR and IR spectra show characteristic features of borate network and compositional dependent trends as a function of Li2O/ZnO concentration. The results are discussed in view of berate network and the dual structural role of Zn2+ ions. The results indicate that the Zn2+ are likely to occupy network-forming positions in this glass system. (C) 2006 Elsevier Ltd. All rights reserved

EPR and Optical Studies of Mo5+ Ions in Lithium Molybdoborate Glasses

Electron paramagnetic resonance (EPR) and optical absorption studies of Li2O–MoO3–B2O3 with varying concentrations of Li2O, MoO3 and B2O3 have been carried out at room temperature. Two series of glasses, one with constant MoO3 (CM) and another with constant borate (CB), have been investigated. Characteristic EPR spectra of Mo5+ have been observed centered around g ≅ 2.00, which are attributed to Mo5+ ion in an octahedral coordination sphere with an axial distortion. The spectra also show strong dependence on the concentration of Li2O and B2O3. Spin concentrations (N) and magnetic susceptibilities (χ) have been calculated. In the CM series, the N values decrease with increasing Li2O content up to 30 mol%, while in the CB series variation of N is found to increase initially up to 20 mol%, and with further increase in the Li2O content the N values tend to decrease. The variation of magnetic susceptibilities is almost similar to that observed with the variation of N. From the optical absorption spectra, an absorption edge (α) has been evaluated. In the CM series, the values of α show a blueshift. On the other hand, in the CB series a redshift is observed. The observed variations in spectral parameters are explained by considering the molybdoborate network. Addition of Li2O to the CM and CB series results in modification of [MoO6/2]0 → [MoOO5/2]− and [BO3/2]0 → [BO4/2]− → [BOO2/2]− groups, respectively, leading to creation of nonbridging oxygens. The optical basicity of the glasses has been evaluated in both the CM and the CB glasses. The optical basicity can be used to classify the covalent-to-ionic ratios of the glass, since an increasing optical basicity indicates decreasing covalency. It is observed that the covalency between Mo5+ ions and oxygen ligands increases in the CB series, whereas in the CM series the covalency between Mo5+ ions and oxygen ligands decreases

Effect of Thermal Aging and Chemical Treatment on Tensile Properties of Coir Fiber.

Effect of thermal aging and chemical treatment on the physical propertiesof coir fiber was investigated. Coir fibers were treated with sodium hydro-xide and glutaraldehyde for 2 h. The influence of alkali and aldehydetreatment on tensile strength and elongation at break was studied in detail.Enhancement in tensile strength of coir fiber was observed up to five daysof aging at 50°C and further decreased. Thermal cross linking of cellulosepresent in the fiber may be the reason for the increase in tensile strengthand thermal degradation due to the chain scission of cellulose reduced thetensile strength. Sodium-hydroxide-treated samples showed an increase intensile strength and reduction in elongation at break. The removal ofimpurities such as waxy and fatty acid residues from the coir fiber byreacting with strong base solution improved the strength of fiber. Crosslinking of cellulose with glutaraldehyde in the fiber reduced the elasticityand enhances the strength of the material. Scanning electron microscopywas employed to analyze the change in surface morphology upon chemicaltreatment. Improvement in the tensile strength suggests that NaOH andglutaraldehyde can be effectively used to modify coir fiber with excellentphysical properties

EPR Study of Fe 3+ - and Ni 2+ -Doped Macroporous CaSiO 3 Ceramics

Thermally stable macroporous CaSiO 3 , Fe 3+ - and Ni 2+ -doped (0.5 to 5 mol%) ceramics have been prepared by solution combustion process by mixing respective metal nitrates (oxidizers), fumed silica. Diformol hydrazine is used as a fuel. The combustion products were identified by their X-ray diffraction and thermal gravimetry/differential thermal analysis. Single phases of β-CaSiO 3 and α-CaSiO 3 were observed at 950 and 1200 °C, respectively. The phase transition temperatures of combustion-derived CaSiO 3 were found to be lower compared to those obtained via solid-state reaction method. It is interesting to note that with an increase in the calcination temperature the samples become more porous with an increase in the pore diameter from 0.2 to 8 µm. The electron paramagnetic resonance (EPR) spectrum of Fe 3+ ions in CaSiO 3 exhibits a weak signal at g = 4.20 ± 0.1 followed by an intense signal at g = 2.0 ± 0.1. The signal at g = 4.20 is ascribed to isolated Fe 3+ ions at rhombic site. The signal at g = 2.0 is due to Fe 3+ coupled together with dipolar interaction. In Ni 2+ -doped CaSiO 3 ceramics the EPR spectrum exhibits a symmetric absorption at g = 2.23 ± 0.1. This deviation from the free electron g -value is ascribed to octahedrally coordinated Ni 2+ ions with moderately high spin–orbit coupling. The number of spins participating in resonance and the paramagnetic susceptibilities have been evaluated from EPR data as a function of Fe 3+ as well as Ni 2+ content. The effect of alkali ions (Li, Na and K) on the EPR spectra of these ceramics has also been studied

EPR and optical absorption studies of Fe3 ions in sodium borophosphate glasses

Electron paramagnetic resonance (EPR) and optical absorption spectral investigations have been carried out on Fe3 ions doped sodium borophosphate glasses (NaH2PO4B2O 3Fe2O3). The EPR spectra exhibit resonance signals with effective g values at g=2.02, g=4.2 and g=6.4. The resonance signal at g=4.2 is due to isolated Fe3 ions in site with rhombic symmetry whereas the g=2.02 resonance is due to Fe3 ions coupled by exchange interaction in a distorted octahedral environment. The EPR spectra at different temperatures (123295 K) have also been studied. The intensity of the resonance signals decreases with increase in temperature whereas linewidth is found to be independent of temperature. The paramagnetic susceptibility (Ï) was calculated from the EPR data at various temperatures and the Curie constant (C) and paramagnetic Curie temperature (θp) have been evaluated from the 1/Ï versus T graph. The optical absorption spectrum exhibits bands characteristic of Fe3 ions in octahedral symmetry. The crystal field parameter (Dq) and the Racah interelectronic repulsion parameters (B and C) have also been evaluated and discussed. © 2010 Elsevier Ltd

Synthesis, structural and transport properties of nanocrystalline La1−xBaxMnO3 (0.0≤x≤0.3) powders

Nanocrystalline La1−xBaxMnO3 (0.0≤x≤0.3) manganites have been prepared by a simple and instantaneous solution combustion method, which is a low temperature initiated synthetic route to obtain fine-grained powders with relatively high surface area. The phase purity and crystal structure of the combustion products are carried out by powder X-ray diffraction. The as-made nanopowders are in cubic phase. On calcination to 900 °C, barium doped manganites retain cubic phase, whereas barium free manganite transformed to rhombohedral phase. The scanning electron microscope (SEM) results revealed that the combustion-derived compounds are agglomerated with fine primary particles. The doped manganites have surface area in the range 24–44 m2/g. The surface area of the manganites increases with barium content, whereas it decreases on calcination. Both undoped and doped lanthanum manganites show two active IR vibrational modes at 400 and 600 cm−1. The low temperature resistivity measurements have been carried out by four-probe method down to 77 K. All the samples exhibit metal–insulator behaviour and metal–insulator transition temperature (TM–I) in the range 184–228 K and it is interesting to note that, as the barium content increases the TM–I shifts to lower temperature side. The maximum TM–I of 228 K is observed for La0.9Ba0.1MnO3 sample

Swift heavy ion irradiation induced phase transformation in calcite single crystals

Ion irradiation induced phase transformation in calcite single crystals have been studied by means of Raman and infrared spectroscopy using 120 MeV Au 9+ ions. The observed bands have been assigned according to group theory analysis. For higher fluence of 5Ã10 12 ion/cm 2, an extra peak on either side of the 713 cm -1 peak and an increase in the intensity of 1085 cm -1 peak were observed in Raman studies. FTIR spectra exhibit extra absorption bands at 674, 1589 cm -1 and enhancement in bands at 2340 and 2374 cm -1 was observed. This might be due to the phase transformation from calcite to vaterite. The damage cross section (Ï) for all the Raman and FTIR active modes was determined. The increase of FWHM, shift in peak positions and appearance of new peaks indicated that calcite phase is converted into vaterite. © 2009 Elsevier Ltd. All rights reserved

Influence of Chemical Treatment on Thermal Decomposition and Crystallite Size of Coir Fiber.

Coir fibers were treated with sodium hydroxide (NaOH) and glutaraldehyde (GA). The influence of alkali and aldehyde treatment on thermal degradation and crystallinity of coir fiber was studied in detail. Thermogravimetric analysis and X-ray diffraction techniques were mainly used to characterize the coir samples. Activation energy of degradation was calculated from Broido and Horowitz–Metzger equations. NaOH-treated samples showed an increase in thermal stability. Removal of impurities such as waxy and fatty acid residues from the coir fiber by reacting with strong base solution improved the stability of fiber. Crosslinking of cellulose with GA in the fiber enhanced the stability of the material. Scanning electron microscopy was employed to analyze the change in surface morphology upon chemical treatment. Improvement in the properties suggests that NaOH and GA can be effectively used to modify coir fiber with excellent stability

Photoluminescence studies of 100 MeV Ni8+ ion irradiated Al2O3 single crystals

We present the results of photoluminescence (PL) measurements on 100 MeV Ni8+ ion irradiated Al2O3 single crystals in the fluence range 1 × 1011 to 5 × 1012 ions/cm2. A sharp PL peaks at ∼693, 695, 707 and 730 nm are recorded with an excitation of 442 nm He–Cd laser beam. The sharp emission peaks at 693 and 695 nm are attributed to R2 and R1 lines of Cr3+ ions, and they are related to the transition from 2Eg → 4A2g. The weaker sharp peaks called N lines appear at ∼707 nm and its origin is ascribed due to closely coupled pairs of Cr3+ ions. The longer wavelength part of the PL spectra at ∼730 nm may be due to increase of groups of more than two Cr3+ ions. It is observed that the broad emission band (450–650 nm) consists of four bands centered at 470, 518, 547 and 618 nm, respectively. The 470, 518 and 547 nm bands are corresponding to F2+, F2 and F22+ defect center, respectively. It is observed that the PL intensity of F2, F22+, R and N lines increases with Ni8+ ion fluence. This can be attributed to increase in concentration of color centers responsible for luminescence through radiative recombination. PACS 61.80.−jh; 61.10.−Nz; 68.37.Ps; 78.66.−

Magnetoresistive studies on nanocrystalline la0.8Sr 0.2MnO3+δ manganite

Low-temperature magnetoresistance (MR) measurement has been carried out on nanocrystalline La0.8Sr0.2MnO3+δ manganites prepared by combustion synthesis. This preparation method yields voluminous powders with large surface area (â¼40m2/g) having crystalline nanosize(-50 nm) products. Formation and homogeneity of the solid solutions have been confirmed by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). Rietveld refinement of X-ray data indicates that as-formed compound exhibits cubic phase with space group Pm3m. However, calcined sample transforms into rhombohedral phase with space group R-3c. The stabilization of the cubic phase in as-formed manganite is due to the substitution of Sr2+ on La3+ sites, resulting in higher Mn4+ content. The low-temperature resistivity measurements down to 70 K exhibit a broad metal-insulator transition (TM-I) at around 257 K. MR measurements on sintered pellets show â¼5 MR at 1T, whereas for 4 and 7T, the MR values are found as 22 and 28, respectively, at TM-I. © 2008 Elsevier B.V. All rights reserved