Variably doped ZnO samples by the sol-gel process have been tested for response to humidity and industrial gases of CO, CH4, NH3 and H-2. The elements of Cobalt (Co) and Indium (In) either singly doped or co-doped at 5 wt% and annealed at varying temperature were observed to increase their grain sizes with annealing temperature while their lattice parameter decrease or increase depending on the dopant ionic radii when compared to the ionic radius of Zn. Co-doping of In and Co, at 5 wt% each, is found to increase the response to all stimuli to higher values than undoped or singly doped ZnO sensors at the expense of selectivity where In-Co-ZnO as well as undoped ZnO and Co-ZnO sensors have similar selectivity value of below 44% to CO. In-doped ZnO shows a distinct selectivity of 60% to NH3. Ionic radii of the In and Co as well as the ionization potentials of the gases have been used to explain the mechanisms of these selective responses. (c) 2017 Elsevier B.V. All rights reserved.

Titania is a cheap and nontoxic polymorphic material of current interest for a variety of technological applications. Generally, TiO2, with a band gap of 3.2 eV, can only be excited by a small UV fraction of solar light, which accounts for only 3-5% of the solar energy. Various strategies have been pursued including doping with metallic elements (e.g., iron) or nonmetallic elements (e.g., nitrogen). In the present work TiO2 was doped with palladium (Pd), platinum (Pt), silver (Ag) and gold (Au) at doping levels of 5% weight, following the standard sol-gel methods. Structural characterization was carried out using scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman Spectroscopy (RS) and X-ray absorption near edge structure (XANES). Palladium and silver initially form oxides but annealing at high temperatures, convert to Pd and Ag metals whereas traces of Au and Pt are observed even at lower temperatures.

Vanadium (VOx) nanoparticles (NPs) prepared by hydrothermal microwave method have been characterized and tested for methane (CH4) detection. The particles structures composed of sphere-like mixed crystalline and amorphous grains with an average diameter of <= 100 nm. High BET surface area of 67 m(2)g(-1) and nano porous property of 16 nm was observed. Room temperature sensing of CH4 gas by VOx NPs was achieved with optimal responsivity as oppose to the performance of other fundamental metal-oxide materials. The sensor response profile follows the underlying mechanism between VOx and CH4.

Sol gel synthesized titania, a large band gap semiconductor, was doped with Ag and Cu in order to compare the structural and optical properties of undoped, single-doped and double-doped species. The nanosized powders were dried at 100 degrees C and then annealed at 300 degrees C, 600 degrees C, 900 degrees C and 1100 degrees C. Structural investigation techniques, including XRD, Raman and SEM, revealed the presence of brookite-mixed phases in the double doped species which may account for the enhancement of the well-known anatase-to-rutile phase transition at high temperatures. This phase mixing is also believed to be responsible for the narrowing of the energy gap of titania, as evident in the UV-visible measurements carried out on the samples.

A combination of both Raman and Brillouin scattering experiments as well as Molecular Dynamics (MD) was used to study the superionic behaviour of BaF2 doped with a wide range of LaF3 concentrations (0⩽x⩽50mol%). Raman spectroscopy reveals that for undoped BaF2 and those doped with 5% and 10% LaF3, the room temperature spectra show the usual T2g symmetry mode at 241cm−1 whereas for those doped with 20%, 30% and 50% LaF3, the dominant Raman mode is of the Eg symmetry situated at ∼263, 275 and 286cm−1, respectively. The Raman linewidths show near linear increases with temperature followed by rapid increases above the characteristic transition temperatures (Tc), being at 1200, 850, 800, 975, 950 and 920K for LaF3 concentrations of 0, 5, 10, 20, 30 and 50; respectively. The temperature dependence of the squares of the Brillouin frequencies (ΔωB)2 of the LA and TA acoustic modes respectively related to elastic constants C11 and C44 showed linear decreases followed by significant deviations around the same temperatures (Tc), at which the Raman linewidths start to show substantial increases. The complementary studies using MD simulations show that the diffusion coefficients increase markedly above the same temperatures observed experimentally. The extrinsic fluorine ion trajectories were also determined from the MD simulations to better understand the mechanisms of diffusion.

We report on the magnetic property of 0.67–WO3+0.33–VOx mixture film deposit on the corning glass substrate using the chemical sol–gel and atmospheric pressure chemical vapor deposition (APCVD) methods. The XRD and Raman spectroscopy confirm species of both materials, and the morphological studies with FIB-SEM and TEM reveal segregation of W and V atoms. XPS reveals that V4+ from VO2 forms only 11% of the film; V3+ in the form of V2O3 form 1% of the film, 21% is V5+ from V2O5 and 67% is given to W6+ from WO3. The analysis of the ESR data shows some sharp changes in the magnetism near the metal-to-insulator (MIT), which could be theoretically interpreted as the ordering or alignment of electron spins from net moment nature to parallel alignment of magnetic moment. The derivatives of magnetic susceptibility established the thermally induced magnetic property: two distinct transitions of 339 K for heating data and 338 K for cooling data for 151.2 mT field were obtained. Similar results were also obtained for 308.7 mT field, 336 K for heating data and 335 K for cooling data. VSM results confirm a paramagnetic phase with a small amount of magnetically ordered phase.

With titanium isopropoxide as the precursor, single and double doped nanosized powders of TiO2 were synthesised by the sol-gel process. The metal dopants used were Ag and Cu at doping levels of 5% (molar weight). The samples were dried at 100 degrees C in air and then heated at 300 degrees C, 600 degrees C, 900 degrees C and 1100 degrees C for one hour. Structural characterisation of the samples was carried out by X-ray Diffraction (XRD), Raman and Scanning Electron Microscopy (SEM) techniques. The results suggests that the co-doped TiO2 powders are constituted by both the anatase and brookite phases whereas only anatase is observed in the case of pure and singly doped samples. The co-existence of brookite with anatase in the codoped sample is thought to be responsible for the enhancement of anatase to ruffle transformation. UV-visible measurements were done to study the optical properties of the TiO2 nanoparticles. Double doping was found to enhance the narrowing of the band gap, compared to single doping.

The sol gel technique was successfully used to synthesize the nanocrystals of tin dioxide (SnO2), co-doped with aluminium (Al) and yttrium (Y). The powders were preheated at different temperatures ranging from 200 to 1000 degrees C. The effects of temperature and dopants on the structure of tin dioxide nanoparticles were investigated. X-ray powder diffraction (XRD) and Raman spectroscopy were used to probe the structural properties. The average crystallite sizes were found to be in the range between 2.5 - 8 nm in the temperature range studied. Both techniques confirm that at higher temperatures there is a high temperature reaction resulting in the formation of yttrium stannate

Samples of undoped CdO and 5% Ag doped CdO nanoparticles were prepared by sol-gel method and annealed for 1h at various temperatures ranging from 100 - 500 degrees C. The prepared samples were characterized using XRD, UV-Vis, Photoluminescence and SEM. The results showed that for 5% Ag-CdO, the nanoparticles were completely crystallized at the annealing temperature of 400 degrees C. Almost similar lattice parameters were obtained for both the undoped and Ag doped CdO nanoparticles. Ag dopant appears to reduce the average grain size of CdO, although it increased as the annealing temperature was raised. Introduction of Ag in CdO resulted in the band gap widening and an increase in the recombination rate.

Nanocrystals of Al and Y co-doped SnO2 were successfully synthesized using the sol–gel method. The samples were subjected to different temperatures ranging from 200 to 1,000 °C. The effects of Al and Y combinational doping and temperature on the structural and optical properties of SnO2 nanoparticles as well as morphology were investigated. The characterization techniques used were X-ray powder diffraction, Raman spectroscopy, scanning electron microscopy and UV–Visible spectroscopy. In the temperature range studied, the average particle sizes were found to be in the range between 2.6 and 8.0 nm, strains were ranging from 2.57 to 0.53 and the optical band gap between 3.31 and 3.99 eV. Both Raman and X-ray diffraction revealed the formation of yttrium stannate at high temperatures.

The possibility of obtaining vanadium dioxide (VO2) [wherein the vanadium ionic state is 4(+)] from a precursor of ammonium metavanadate (NH4VO3) bearing the ion V5+ is investigated. The reduction is carried out by calcining the NH4VO3 powders in similar concentrations of H-2 flow at varying temperatures. The resulting powders have been studied by several techniques including XRD, Raman spectroscopy, FTIR, TEM, BET and DSC. It is found that remnants of bright yellow V5+ still exist up to calcination temperatures of 100 degrees C after which the sky-blue VO2 dominates at calcination temperatures of 150 degrees C -250 degrees C. There is a population surge of metastable dark-blue V6O13 (where V is in between V4+ and V5+ ionic states) between 250 degrees C and 300 degrees C. However above 350 degrees C the material reverts to the stable V5+ in the yellow orange V2O5. XPS/EDS and VSM confirm the order of appearance to be VO2(150 degrees C) -> V6O13(200 degrees C) -> V2O5 (350 degrees C). (C) 2014 Elsevier B.V. All rights reserved.

Different forms of tin-dioxide (SnO2) ceramic have been thoroughly studied in recent years because of its potential in sensing and fuel cells. The current findings used classical molecular dynamics simulations focused on the role of defects in tin-dioxide. The total energy of the NPT hoover ensemble at various temperatures has been calculated in order to determine the effects of oxygen vacancy and Ti substitutional defect in tin-dioxide. The results obtained suggest that Ti defect tends to lower the energy of the anatase tin-dioxide with increasing temperature. The radial distribution functions and the volume-temperature plots of the structures suggest the transformation of anatase to rutile tin-dioxide around 3000 K.

TiO2 nanopowders, single and double doped with Ag and Cu, were prepared using the sol-gel method, with titanium isopropoxide as the precursor. For comparison, an undoped sample was also prepared. The synthesised samples were calcined to a temperature of 300 degrees C and characterised by X-ray diffraction (XRD), Raman and scanning electron microscopy (SEM) techniques. The single-doped powders (as well as the undoped sample) featured only the anatase phase. The co-doped powder was found to be constituted by anatase and brookite phases. The results suggest that multiple doping of titania may favour a two-phase structure at lower temperatures than single doped powders.

Tin-dioxide ceramics have been intensively studied in recent years because of their potential in sensing and fuel cells. The present work uses classical molecular dynamics simulations focused on the role of defects in tin-dioxide. The total energy of the NPT Hoover ensemble at various temperatures has been calculated in order to determine the effects of oxygen vacancy and Ti substitutional defect in tin-dioxide. The results obtained showed an energy increase with temperature which was constantly compared with experiments. The radial distribution functions for the structures suggest the transformation of anatase to rutile tin-dioxide at high temperature.

In this paper, the formulation of the Tersoff bond-order potential was used to study the structural and thermodynamics properties of bilayer graphene (BLG). The simulations were performed within a canonical (NVT) ensemble for structural properties and isothermal isobaric ensemble (NPT) for thermodynamic properties. Each double layer is a hexagonal arrangement of carbon atoms at the corners to make up a two dimensional honeycomb sheet. One model consists of 64 carbons (graphene64); the other model has 256 carbon atoms (graphene256). Using the structural optimization and radial distribution functions, some equilibrium properties of these layered graphene structures are noted. Thermodynamic properties will be investigated to understand the behaviour of graphene at high temperatures.

Nanocrystals of Y and Zr doped SnO2 have been prepared by sol-gel route and annealed at 200, 400, 600, 800 and 1000 ºC. The X-ray diffraction (XRD) results showed the average size of the particles in the freshly prepared samples to be ~ 3 nm. The Extended Absorption Fine Structure (EXAFS) technique was used to study the dopant environments in nanocrystalline tin oxide. In all Y-doped samples, except the one annealed at 1000 ºC, there is clear evidence that Y has not entered the SnO2 lattice. This is clearly supported by the Raman scattering results. In all Zr-doped samples, there is a simple substitution for Sn by Zr.

Au, Ag, Pt and Pd doped TiO2 nanocrystals were prepared using sol-gel routes. X-ray Near Edge Structure (XANES) was used to study the location of these precious metal dopants in nanocrystalline TiO2. The effects of these dopants on the phase transformation and grain growth were investigated using X-ray diffraction (XRD). Two dopant concentrations i.e. 1 and 5% were studied and similar results were found. Silver and Palladium initially form oxides but annealing at high temperatures converts them to metals. Gold and and silver do not affect the anatase - rutile transformation temperature whereas palladium and platinum do. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The squares of the Brillouin frequencies (Deltaomega(B))(2) of the LA mode in the [100] direction related to the Cl, elastic constant show a linear decrease with temperature followed by significant deviations that occur above the corresponding transition temperatures (T-c), being at 850, 800, 970, 950 and 920 K for samples with x = 0.05, 0.1, 0.2, 0.3 and 0.5, respectively. The Raman linewidths show linear increases with temperature followed by rapid increases around the same temperatures at which the elastic constants start to show marked decreases. The complementary studies using Molecular Dynamics show that the diffusion coefficients start to increase markedly around the same temperatures observed experimentally.

High temperature Brillouin and Raman light scattering studies have been used to study the transition to the superionic state of CaF2 (10 mol%LaF3) and CaF2 (10 mol%TbF3) over the range 300 to 1200 K. The Brillouin scattering results yield the temperature dependence of the elastic constant C11. that undergoes a marked decresase above the transition temperature Tc while the Raman measurements of the width of the peak ay 310 cm–1 show a corresponding substantial broadening. The transition temperatures are ∼900 K in CaF2 (10 mol%LaF3) and ∼1000 K in CaF2 (10 mol%TbF3). Molecular dynamics simulations of fluorine diffusion in both systems closely reproduces the transition temperatures as well as the details of the higher temperature behaviour of the Brillouin and Raman signatures. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)