Publications
Publications
Effect of La- and/or Nb-doping on structure and elastic behavior of BaFeO3−𝛿 at room temperature and 850 ◦C were studied and compared. The Comparison of the microstructures and grain size distributions of densified Ba0.95La0.05FeO3−𝛿 (BLFO), BaFe0.9Nb0.1O3−𝛿 (BFNO) and B0.95La0.05aFe0.9Nb0.1O3−𝛿 (BLFNO) showed that Nbdoping hindered grain growth during sintering. The XRD analyses of sintered samples demonstrates that La-doping is more effective than Nb-doping for stabilization of high temperature symmetric cubic structure as it proved by BLFO’s linear elastic behavior in cyclic compression stress–strain curves. BFNO and BLFNO exhibited ferroelastic behavior at room temperature due to presence of non-symmetric phases in their structures. All samples showed linear elastic behavior at 850 ◦C with remnant strain due to high temperature creep deformations. Both La- and Nb-doping can improve creep resistance of BaFeO3−𝛿.
BaFeO3−𝛿 (BFO) and BaFe0.9Zr0.1𝑂3−𝛿 (BFZO) oxides were synthesized by sol–gel method and their mechanical properties in room temperature and 850 ◦C were investigated and compared. The Rietveld refinement of the sintered samples at 1300 ◦C/10 h revealed that Zr-doping stabilized the symmetric cubic structure in BFZO from a multiphase (hexagonal and cubic) crystal structure in BFO. The room temperature non-linear stress– strain curves of BFO revealed its ferroelastic behavior due to the ferroelastic domain stitching under stress. In contrary, BFZO at room temperature and both BFO and BFZO at 850 ◦C exhibit linear elastic behavior as they have symmetric cubic crystal structure. The high temperature mechanical testings show that Zr-doping can also improve creep resistance of BFO.
Octahedral shaped Fe 3 O 4 and α-Fe 2 O 3 nanoparticles were prepared by simple chemical oxidation method. The prepared magnetic nanoparticles were surface modified with carbon using sugar solution as a carbon source. The crystallinity, structural and morphological studies through XRD, FESEM and TEM analysis confirmed the successful formation of the desired nanostructures. The obtained carbon modified octahedral shaped Fe 3 O 4 nanoparticles exhibited a larger saturation magnetization of 87 emu/g. Further, the carbon modified magnetic hybrid nanoparticles were exploited as a negative electrode material for supercapacitor application and observed a high specific capacitance value of 274 F/g for the post annealed samples. The enhanced specific capacitance value is due to the fraction of carbon in hybrid material and it could be enhanced further by increasing the carbon fraction. The cycle stability performance was tested with 5 A/g and showed 83% retention even after 5000 cycles.
DOI: 10.1016/j.apsusc.2019.04.177
Ferroelastic mechanical behavior of LaCoO3 was investigated by the impression test and compared with the conventional compression test using digital image correlation technique for deformation measurement. The results show that the coercive stress for ferroelastic deformation can be detected by impression test, which is less than critical stress for such deformation in the compression test. Room temperature ferroelastic impression creep characterization showed different equilibrium penetration of flat-end punch at different constant stresses, which can be characterized by Prony series.
We report optical and spectroscopic investigations on polyvinyl alcohol (PVA)/silica composite free standing films. Amorphous silica nanoparticles are synthesized from rice husk ash using pyrolysis technique. PVA/silica nano composite free standing films are prepared by simple chemical method. As prepared nano composites are characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, photoluminescence spectroscopy (PL) and time resolved photoluminescence (TRPL) spectroscopy techniques. Spectroscopic studies reveal the structural modification of silica nanoparticle in PVA matrix due to the formation some new chemical bonds. The prepared PVA/Silica composites exhibit exceptional optical properties which can be applicable for Opto-electronic device applications.
DOI: 10.1016/j.optmat.2019.01.063
Chitosan (CH) capped inorganic nanomaterials have been considered as significant antibacterial materials in the clinical field. This work shows the synthesis of two new different antibacterial composite films as a result of the incorporation of CH capped copper oxide (CHCuO) and copper (CHCu) nanoparticles (NPs). Here, CHCuO and CHCu NPs were achieved by a facile chemical reduction of Cu 2+ ions using sodium hydroxide and ascorbic acid. TEM analysis revealed the morphology as rod-type nanoflakes for CHCuO and a spherical shape for CHCu NPs with ~7 ± 2 nm size. Antimicrobial activity of the developed materials was studied by the inhibition zone method, against both gram-negative and gram-positive bacteria. The antimicrobial activity revealed that the CHCuO NPs and CHCuO-CH film showed a higher inhibition zone than the other nanomaterials. The results suggested that the synthesized materials can be used in wound dressing applications.
Abstract
Structural and mechanical Characterizations of La1.8M0.2NiO4+δ (M: Sr and Ba) prepared by low frequency ultra-sound assisted synthesis technique and sintered at different temperatures were studied. HRTEM and XRD analyses showed the uniform shape of calcined nanocrystalline powders with the particle size of less than 100 nm with mixed phases, which were refined by Rietveld method using orthorhombic (Fmmm) and tetragonal (F4/mmm) structures. Sintering La1.8Sr0.2NiO4+δ and La1.8Ba0.2NiO4+δ compacted discs at temperatures higher than 1300 °C and 1250 °C, respectively, resulted in appearance of extra peaks close to a monoclinic phase. Doping La2NiO4+δ with Sr2+ and Ba2+ did not affect its sinterability and average grain size significantly, however, Ba2+ improved the elastic modulus and microhardness, while Sr2+ improved the fracture toughness.
Abstract
In this work, we present the synthesis of Ag doped TiO2 materials. The products are characterized by powder X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, nitrogen adsorption, and hydrogen adsorption. The Ag/TiO2materials exhibit 3.65 times higher in hydrogen adsorption capability compared with the non-doped TiO2 materials thank to the existence of Ti3+ species, which are Kubas-type hydrogen adsorption centers, and the Ag nanoparticles which provide spillover effects. We believe that this is the first time that both Kubas-type adsorption and spillover are exploited in the design of novel hydrogen storage materials.
The effect of molecular weights and hydrolysis degrees (HD) of polyvinyl alcohol (PVA) on thermal and mechanical properties and crystallinity of polylactic acid (PLA)/PVA blends was investigated. Blends were prepared by the melt blending method using PLA/PVA ratios: 80/20, 90/10 and 97/3 wt. %. A single glass transition temperatures was observed for all PLA/PVA blends, suggesting the formation of binary compatible blends at concentration range studied. Thermogravimetric analysis results showed a better thermal stability for PLA/PVA blends containing PVA of higher Mw and HD. According to mechanical properties, low quantities of PVA (3 wt. %) do not affect the tensile strength of blends (irrespective of Mw and HD). However, as the PVA content increases, tensile strength tends to lower values, especially for blends with 20 wt.% of PVA, with 98% of HD.
Abstract
Flash sintering technique was applied to Ce0.9Gd0.1O1.95 (10GDC) electrolyte fabricated by tape-casting at different temperatures under various electric fields. Densification of the electrolyte at constant electric field depended mainly on the current passing through the sample. The applied electric field influenced the temperature at which the flash sintering occurred. To achieve the microstructure with high densification, a suitable current density must be selected. The temperature for flash sintering varies with the materials and the contact area between the particles, which changes with the particle size, the porosity and the inhomogeneity.
Abstract
Nanopowders of Ce0.9RE0.1O1.95 (RE=Nd, Y, Pr and Er) were synthesized by nitrate-fuel combustion method and calcinated at 700 °C for 2 h to obtain completely crystalline structures. The effect of RE dopants on the crystalline nature, lattice parameters, and microstructural parameters such as microstrain, stress, and deformation energy density of ceria was evaluated through uniform deformation model (UDM), uniform deformation stress model (UDSM) and uniform deformation energy density model (UDEDM) by using the X-ray diffraction (XRD) data. The results revealed that the microstructural parameters were considerably altered with respect to the dopants. The transmission electron microscope (TEM) graphs and their corresponding selected area diffraction (SAED) patterns of ceria nanoparticles confirmed that all doped ceria powders are crystalline with the wide range of particle size distributions aligned in all the directions. The optical diffuse reflectance spectroscopy (DRS) measurements showed a band at around 340 nm attributed to the transitions of charge-transfer between O 2p and Ce 4f orbitals in cerium oxide and RE doped CeO2 exhibited the reflectance band in the visible regions due to the transition of 4f energy levels of RE ions. Photoluminescence (PL) spectra of RE doped ceria showed the blue-green emission bands.
Abstract
La0.6Sr0.4M0.1Fe0.9O3-δ (M: Co, Ni and Cu) perovskite nanostructures were synthesized using low frequency ultrasound assisted synthesis technique and effect of substitution of Fe by Co, Ni and Cu on crystal structure and mechanical properties in La0.6Sr0.4FeO3-δ perovskite was studied. The HRTEM and Rietveld refinement analyses revealed the uniform equi-axial shape of the obtained nanostructures with the existence of La0.6Sr0.4M0.1Fe0.9O3−δ with mixed rhombohedral and orthorhombic structures. Substitution by Cu decreases the melting point of La0.6Sr0.4FeO3-δ. The results of mechanical characterizations show that La0.6Sr0.4Co0.1Fe0.9O3−δ and La0.6Sr0.4Ni0.1Fe0.9O3−δ have ferroelastic behavior and comparable elastic moduli, however, substitution by Ni shows higher hardness and lower fracture toughness than Co in B-site doping.
Molybdenum-doped ceria (CMO) is a promising material for the fabrication of anodes for carbon-air fuel cells. In this work, Ce0.9Mo0.1O2+δ was synthesized by the combustion method, which reports lower synthesis times than the solid-state reaction and Pechini methods. The material obtained does not present impurities (determined by EDS analysis) and forms Fm-3m (225 space group) single phase fluorite-type structures with a cell parameter of ca.5.419 Å (determined by Rietveld refinement). The mechanical properties of this material were studied using dense pellets produced by pressing the powders (pressure of ca. 105 MPa) and sintering the tablets obtained at 1000°C for 24 hours. The Young’s modulus (291.7 GPa) and Vickers microhardness (between 4694 and 2474.4 MPa) were determined by using the resonant frequency method and Struers microhardness tester, respectively. Future work considers the complete characterization of mechanical and electrical properties of CMO with different amounts of dopant.
Abstract
Structural characteristics of combustion synthesized, calcined and densified pure and doped nanoceria with tri-valent cations of Er, Y, Gd, Sm and Nd were analyzed by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). The results showed that the as-synthesized and calcined nanopowders were mesoporous and calculated lattice parameters were close to theoretical ion-packing model. The effect of dopants on elastic modulus, microhardness and fracture toughness of sintered pure and doped ceria were investigated. It was observed that tri-valent cation dopants increased the hardness of the ceria, whereas the fracture toughness and elastic modulus were decreased.
Abstract
In the present work, the pure CeO2 and yttrium doped CeO2 nanopowders were synthesized by the nitrate-fuel self-sustaining combustion method and calcined at 700 °C for 2 h. X-ray diffraction (XRD) and high resolution electron transmission microscopy (HRTEM) results demonstrated a cubic fluorite with high purity and the crystallite sizes less than 20 nm calculated from Scherrer’s formula. The BET specific surface area of yttrium doped CeO2 samples showed high values than those of pure CeO2. The photocatalytic activity of yttrium doped CeO2 showed high degradation of Rhodamine B solution under visible light illumination.
Abstract
La0.6Sr0.4Co0.2Fe0.8O3 − δ (LSCF) perovskite nanostructures were synthesised using a 42 kHz ultrasound assisted synthesis technique for the fabrication of electrodes in the intermediate and/or low temperature solid oxide fuel and electrolysis cells (SOFCs/SOECs). The obtained nanomaterials were dried at 110 °C followed by calcination in a normal atmosphere at various temperatures from 400 to 1000 °C for 2 h. Powder characteristics such as crystal structure, thermal decomposition, particle size and morphology were analysed. The transmission electron microscopy (TEM) study revealed the uniform equi-axial shape and growth of the obtained nanostructures with respect to the calcination temperature till 800 °C. The structural and chemical analyses confirmed the existence of LSCF and CoFe2O4 phases.