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Faceted nanocrystals involving Ce1−xZrxO2 (CZ) system bound by (101) and (l10) facets were synthesized via co-precipitation route. The novelty of this process relies on the fact that the synthesis did not involve any surfactant/ligand for morphology control (for all the CZ compositions) and the nanocrystals retained their shapes at high temperatures (> 800 °C). Catalytic and photocatalytic degradation properties were suitably examined for the CZ nanocrystals; substantial (∼90%) degradation of the methylene blue dye was observed only in 60 min of visible light irradiation. Ce1−xZrxO2 ceramics with near-theoretical density (>98%) obtained at 1580 °C (for 2 h) confirmed excellent sinterability for the synthesized CZ nanocrystalline powders. The ionic conductivities of the doped-ceria ceramics increased with temperature and frequency. A maximum conductivity of ∼2 × 10−3 S/cm was measured at 600 °C at 1 MHz for Ce0.4Zr0.6O2 ceramic; previous works obtained similar data at 900 °C or beyond for the same composition.

Structure–property correlations were investigated for LaxCe1−xO2−δ (x = 0.05, 0.15) system (for both nanoparticles and ceramic). The nanoparticles were synthesized by the co-precipitation route and characterized for their structural, catalytic and visible light driven photocatalytic properties. Synthesised LaxCe1−xO2−δ nanopowders depicted phase purity with excellent compositional control as confirmed by various structural characterisation tools. The 15% La3+-doped ceria nanoparticles portrayed superior photocatalytic properties; complete degradation (99%) of the methylene blue dye was observed within 60 min of visible light irradiation under an alkaline medium. High density (> 96%) of the ceramics (sintered at 1580 °C for 2 h) confirmed promising sinterability of the synthesised powders. The ionic conductivities of the LaxCe1−xO2−δ ceramics increased with temperature and frequency owing to enhanced oxygen vacancies in the ceria matrix as a result of doping (of La3+-ions); a maximum conductivity of ~ 8.4 × 10−2 S cm−1 was obtained at 900 °C for the 15% La3+-doped ceria ceramics at 1 MHz frequency.

Mixed polyanion glass and glass-ceramic cathodes can have the potential to overcome the disadvantages of achieving high theoretical capacities of promising crystalline network. Three targeted cathode compositions were chosen for the present study (NaFe0.5(VO)0.5PO4, NaMn0.7(VO)0.3PO4 and NaCo0.7(VO)0.3PO4) based on the superior performance over their crystalline counter parts with highest current density ~ 100 mAh/g. XRD results displayed that major crystalline phases (Na2FeP2O7 (COD ID: 4001802), Na2MnP2O7 (ICSD ID: 71229)) which are precipitated with an ordered triclinic, P1 structure. However, Na2CoP2O7 (ICSD ID: 71230) crystalline phase exhibits orthorhombic/P n a 21 structure. The highest conducting glass-ceramic cathode sample NaCo0.7(VO)0.3PO4 (σ = 6.41 × 10−7 S·cm−1) retains its discharge capacity retention as 84.5 mAh g−1 (91%) even after 50 cycles. At a high rate of 10C, NaFe0.5(VO)0.5PO4 cathode sample is achieved to be highest discharge capacity retention 69.7% than NaCo0.7(VO)0.3PO4 (53.76%) which is a significant feature of mixed polyanion family of glass-ceramic cathodes.

The understanding of atomic-scale structure is a prerequisite for establishing the physico–chemical behavior of complex glass systems. To this end, positron annihilation life time spectroscopy (PALS) is an atomic scale probe capable of investigating the subnanoscopic free volume of amorphous materials. In the present work, PALS has been used to quantify the free volume changes as a function of increasing substitution of B2O3 by Al2O3 in strontium borosilicate glasses intended to be used as sealant in solid oxide fuel cells. The free volume parameters; ortho-positronium (o-Ps) life time (τ 3) and intensity (I 3) show composition dependant variations which are correlated to the molar volume and compactness of the glasses through a commutative free volume parameter, $$~\tau _{3}^{3}{I_3}$$ . The effect of change in nanoscopic free volume induced by the substitution of B2O3 by Al2O3 on the glass transition temperature (T g), softening temperature (T s), coefficient of thermal expansion (CTE) and thermal stability of glasses have been studied. A remarkable trend-based variation in these macroscopic properties with change in free volume is observed. We envisage that the findings of this work will provide new insights in establishing subnanoscopic structure and thermo-physical property correlation of complex glass systems containing multiple network former and modifiers.

Glass samples with general formula NaCo1−x (VO) x PO4 (x = 0.1, 0.3, 0.5 and 0.7) are synthesized via a simple melt quenching method followed by high-energy ball milling for 30 h to form the homogeneous nanoscaled glass powders. DTA traces of all the glass and glass–ceramic samples indicated exothermic processes confirming selective crystallization induced in the glass network. The formation of major crystalline phase [sodium cobalt pyrophosphate (Na2CoP2O7)] with an ordered layered structure was monitored by X-ray diffraction and the same was justified by SEM images. Structural illustration of major crystalline Na2CoP2O7 phase offered more intra-layer Co–Co distance (7.12 A) than inter-layer Co–Co distance (5.37 A) which facilitates two-dimensional Na-ion diffusion pathways to achieve the fast intercalation and de-intercalation phenomenon along the a and c directions. The ionic conductivity was monitored by Impedance analysis and achieved to be highest (6.41 × 10−7 S cm−1) for the glass–ceramic cathode x = 0.3, NaCo1−x (VO) x PO4. The initial discharge capacity for the highest conducting NaCo0.7(VO)0.3PO4 cathode is obtained as 93 mA h g−1 in 0.1 C and had 65% capacity retention even at high rate 10 C.

The role of La+3/Sr+2 ratios, which is varied from 0.08 to 5.09, on density, molar volume, packing fraction, free volume, thermal and electrical properties in strontium lanthanum aluminoborosilicate based glass sealants intended for solid oxide fuel cell (SOFC) applications is evaluated. The studies reveal expansion of the glass network evident from increasing molar volume and decreasing packing fraction of glasses with progressive La+3 substitutions. The molecular origin of these macroscopic structural features can be accounted for by the free volume parameters measured from positron annihilation lifetime spectroscopy (PALS). The La+3 induced expanded glass networks show increased number of subnanoscopic voids with larger sizes, as revealed from the ortho-positronium (o-Ps) lifetime and its intensity. A remarkably direct correspondence between the molar volume and fractional free volume trend is established with progressive La2O3 substitution in the glasses. The effect of these structural changes on the glass transition temperature, softening temperature, coefficient of thermal expansion, thermal stability as well as electrical conductivity has been studied.

Citrate-nitrate autocombustion process is a promising synthesis route in the field of nanomaterials. This route involves many controlling parameters which ultimately affect properties of the products. In the present research work, the effect of concentration of fuel to that of metal nitrates has been studied in a systematic manner. The nature of exothermic reaction was analyzed with DSC-TGA and the powder properties were characterized by XRD, TEM and BET measurement. The properties of the powders have been explained with respect to fuel content, vigorousness of the exothermic reaction, combustion temperature and duration. The most vigorous reaction was found to occur for the composition with FER of 0.50 with the production of the smallest crystallite size of 9 nm.

A series of glass sealants for solid oxide fuel cell (SOFC) with compositions SrO (x wt %) La2O3 (15 wt %) Al2O3 (15 wt %) B2O3 (40-x wt %) SiO2 (30 wt %) [x = 10, 15, 20, 25 & 30] [SLABS] have been investigated by quantitative Fourier Transform Infrared Spectroscopy (FTIR). Structural findings from FTIR reveal that with increasing substitu-tion of B2O3 by SrO, even though the B2O3/SiO2 ratio decreases, however the Si-O- non-bridging bond content in the matrix is increasing and glass structure is getting more inverted. UV-Vis Diffused Reflectance Spectroscopy (UV-Vis-DRS) of the glass series shows that electrical band gap of glasses decreases in the series from 3.07eV to 2.97eV with increasing substitution from x = 10 to x = 30. Conductivities of the glass samples were measured by AC impedance spectroscopy and found to be increasing from 2.74 × 10-5 Scm-1 to 1.09 × 10-4 Scm-1 with increasing substitution from x =10 to x = 30.

Nanocrystalline yttrium aluminium garnet (YAG) powder has been synthesised by sucrose combustion method. A foamy mass obtained by drying a resin prepared by heating yttrium nitrate, aluminium nitrate and sucrose undergoes self-sustained combustion when initiated with a burning splinter and produces YAG precursors containing amorphous oxides of yttrium and aluminium. The YAG phase has been obtained from the precursors during calcination at a relatively low temperature of 900°C without the formation of any intermediate compounds. The YAG powder prepared by planetary ball milling of the combustion product calcined at 900°C contained particles in the size range of 0·06 to 5 μm with a D 50 value of 1·04 μm and had a surface area of 21·5 m2 g−1. The YAG particles are aggregate of crystallites of the size nearly 30 nm.

Nanocrystalline yittria-stabilized zirconia (YSZ) compounds with yittria concentration varying between 8 and 12 mol% have been synthesized by gel combustion method followed by heat treatment at 550°C. The YSZs are found to posses stable face centered cubic structure at room temperature by X-ray diffractometry. The lattice parameter ‘a’ showed an increasing trend with increasing concentration of yittria. The crystallite size estimated by Scherrer method was in the range of 7–10 nm. Band gap studies showed an increasing trend with increasing yittria concentration and are found to be consistent with respective lattice parameters following the tight binding approximation or linear combination of atomic orbitals approximation.

A strontiumlanthanumaluminoborosilicate based intermediate temperature solid oxide fuel cell (IT-SOFC) glass sealant has been investigated for isothermal devitrification under accelerated conditions. Sintering of the glass up to 100 h at 1000 degrees C, results in the formation of two crystalline phases evidenced by X-ray diffraction (XRD) analysis. Hexacelsian phase evolves from the initial hours of sintering: however, lanthanum silicate phase appears at longer hours of sintering. Quantitative XRD of the glass ceramics reveals that hexacelsian occupies majority of the crystalline phases and lanthanum silicate is occupying minor quantity. Formation of crystalline phases has been reconfirmed by microstructure analysis of glass ceramics through Scanning Electron Microscopy (SEM) and elemental analysis of phases by energy dispersive spectroscopy (SEM-EDS). Crystalline phases in the glass ceramics have been quantified by analysis of SEM images through Imagepro plus software. At different stages of sintering, CTE of the glass ceramics has been measured by dilatometer. Correlation of CTE with crystalline phases in the glass ceramics indicates that with formation of hexacelsian phase CTE of the glass ceramics increases, however, formation of lanthanum silicate phase reduces the CTE of the glass ceramics. Phase property correlation indicates that after 100 h of accelerated devitrification at 1000 degrees C, the glass ceramics attains phase stability therefore the CTE stabilizes and the value remains well within the requirement limit of SOFC sealant. (C) 2012 Elsevier B.V. All rights reserved.

Strontium-lanthanum-aluminoborosilicate (SrO-La(2)O(3)-Al(2)O(3)-B(2)O(3)-SiO(2)) (SLABS) glass was prepared for sealant material in planar Solid Oxide Fuel Cells (pSOFC). Differential Thermal Analysis of the glass showed the formation of two crystalline phases, first one 807 degrees C and the second phase at 1021 degrees C. Crystallization kinetic of the first crystalline phase was investigated by differential thermal analysis (DTA) and using the JMA-kinetic model. The activation energy for crystallization was calculated to be 114.04 kJ/mol with frequency factor 5.9 x 10(3). Coefficient of Thermal Expansion (CTE) of the glass was measured to be 9.72 x 10(-6)/degrees C. Optical band gap of the glass was measured to be 3.07 eV. Conductivity measured by Impedance spectroscopy found to be 5.68 x 10(-7) S cm(-1) at 600 degrees C and it increased with temperature to 2.68 x 10(-6) S cm(-1) at 800 degrees C. Activation energy for electrical conduction was measured to be 66.12 kJ/mol. Wetting behavior of the glass on a ferritic steel substrate was investigated under hot stage microscopy. It showed initial deformation temperature (IDT) 754 degrees C, softening temperature (ST) 840 degrees C, hemispherical temperature (HT) 1108 degrees C and flow temperature (FT) 1279 degrees C. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

A series of SOFC glass sealants with composition SrO (x), La(2)O(3) (15), Al(2)O(3) (15), B(2)O(3) (40 - x), and SiO(2) (30) [x = 10, 15, 20, 25 and 30] (wt.%) [SLABS] are investigated for their structure property correlations at different compositions. Quantitative Fourier transform infrared spectroscopy shows structural rigidity with increasing SrO content, as demonstrate by an increase in the Si-O-Si/O-Si-O bending and B-O-B stretching frequencies. The role of SrO as a modifier dominates the control of the structure and behaviour of glasses compared with the effect of network formers, i.e., the B(2)O(3)/SiO(2) ratio. Consequent to the structural changes, increasing substitution of B(2)O(3) by SrO the glasses causes increases in the density, glass transition temperature and dilatometric softening point. On the other hand, the crystallization temperatures show a decreasing trend and the coefficient of thermal expansion increases with increase in substitution. (C) 2011 Elsevier B.V. All rights reserved.

Nanocrystalline 8 mol% yttria stabilized zirconia (YSZ) powder was synthesized using polyvinyl alcohol (PVA) as organic precursor and acidic solutions of yttrium oxynitrite and zirconium nitrate. Complex formation was established using Fourier transform infrared (FTIR) spectroscopy and solid state (13)C nuclear magnetic resonance (NMR) spectroscopy. Thermal stability of the complex was investigated by thermogravimetric analysis (TGA). X-ray diffractometry (XRD) revealed formation of cubic phase YSZ at a temperature as low as 600 degrees C. The lattice parameter and average crystallite size were calculated from the XRD data. Particle size of the YSZ powder was investigated through transmission electron microscopy (TEM). The band gap of the sintered YSZ pellet was measured by UV-Vis-diffused reflectance spectroscopy (DRS). AC electrical conductivity was measured in air at 1 kHz frequency using a programmable RCL meter. The activation energy was calculated from the conductivity data at different temperatures using the standard Arrhenius equation. (C) 2009 Elsevier Ltd and Techna Group S.r.l. .