Sharif Digital Repository

The morphological manipulation and structural characterisation of TiO 2-MgO binary system by an aqueous particulate sol-gel route were reported. Different crystal structures including pure MgTiO 3, mixtures of MgTiO 3 and TiO 2 and mixtures of MgTiO 3 and Mg 2TiO 4 were tailored by controlling Mg:Ti molar ratio and annealing temperatures as the processing parameters. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that all compounds crystallised at the low temperature of 500 °C. Furthermore, it was found that the average crystallite size of the compounds depends upon the Mg:Ti molar ratio as well as the annealing temperature, being in the range 3-5 nm at... 

In this paper, a hierarchical multi-scale technique is developed to investigate the thermo-mechanical behavior of nano-crystalline structures in the presence of edge dislocations. The primary edge dislocations are generated by proper adjustment of atomic positions to resemble discrete dislocations. The interatomic potential used to perform atomistic simulation is based on the Finnis-Sinclair embedded-atom method as many-body potential and, the Nose-Hoover thermostat is employed to control the effect of temperature. The strain energy density function is obtained for various representative volume elements under biaxial and shear loadings by fitting a fourth order polynomial in the atomistic... 

In this paper, a multi-scale molecular dynamics-finite element coupling is presented to study the mechanical behavior of heterogeneous nano-crystalline structures. The stiffness and mass matrices of the continuum sub-domain are generated by applying a linear transformation on the matrices obtained via the atomic structure underlying the FE mesh. A Lagrange multiplier method is employed to the transition zone imposing velocity resemblance of the coupling regions. The constraint equations of motion are solved by the multi-time-step decomposition thus giving the opportunity to ascribe different time steps to each individual zone. The molecular dynamics is performed by employing the... 

In this article, a novel approach is presented for the concurrent coupling of continuum-atomistic model in the nano-mechanical behavior of atomic structures. The study is focused on the static concurrent multi-scale simulation, which is able to effectively capture the surface effects intrinsic in the molecular mechanics modeling. The Hamiltonian approach is applied to combine the continuum and molecular models with the same weight in the overlapping domain. A Lagrange-multiplier method is employed over the overlapping domain for coupling the continuum nodal displacement with the atomic lattice deformation. A multiple-step algorithm is developed to decouple the solution process in the atomic... 

The low temperature perovskite-type calcium titanate (CaTiO3) thin films and powders with nanocrystalline and mesoporous structure were prepared by a straightforward particulate sol-gel route. The prepared sol had a narrow particle size distribution about 17 nm. X-ray diffraction and Fourier transform infrared spectroscopy revealed that, the synthesized powders had highly pure and crystallized CaTiO3 structure with preferable orientation growth along (1 2 1) direction at 400-800 °C. The activation energy of crystal growth was calculated 5.73 kJ/mol. Furthermore, transmission electron microscope images showed that the average crystallite size of the powders annealed at 400 °C was around 3.5... 

In this paper, a new multi-scale technique is developed for concurrent coupling of atomistic-continuum domains in modeling nano-mechanical behavior of atomic structures. A Lagrange multiplier method is employed over an overlapping domain to coupling the continuum nodal velocities with atomic lattice velocities. The Hamiltonian method is applied to combine the continuum and molecular Hamiltonians with the same weight in the overlapping domain. The mass and stiffness matrices of the continuum domain are obtained using a linear bridging map of the atomic lattice displacement laid underneath the continuum grid to the element displacements. Numerical examples are performed by presenting the... 

WO3 thin film photoanodes containing different concentrations of Ag nanoparticles were synthesized by solegel method. Based on UV-visible spectra, presence of a surface plasmon resonance peak at 470 nm of wavelength indicated formation of silver nanoparticles in the WO3 films. According to atomic force microscopy (AFM) analysis, the highest value for surface roughness and the effective surface ratio was observed for the sample containing 2 mol% of Ag. X-ray diffraction (XRD) patterns revealed that WO 3 nanocrystalline structure was formed in the monoclinic phase with the average size of about 18.2 nm while Ag nanocrystals were determined in cubic phase. X-ray photoelectron spectroscopy (XPS)... 

The low temperature perovskite-type strontium titanate (SrTiO 3) thin films and powders with nanocrystalline and mesoporous structure were prepared by a straightforward particulate sol-gel route. The prepared sol had a narrow particle size distribution with hydrodynamic diameter of about 17 nm. X-ray diffraction (XRD) revealed that the synthesized powders had a perovskite-SrTiO 3 structure with preferable orientation growth along the (1 0 0) direction. TEM images showed that the average crystallite size of the powders annealed in the range 300-800°C was around 8 nm. FE-SEM analysis and AFM images revealed that the deposited thin films had mesoporous and nanocrystalline structure with the... 

Perovskite-type barium strontium titanate (BST) thin films and powders with nanocrystalline and mesoporous structure were prepared by a straightforward particulate sol-gel route at room temperature. The prepared sol had a narrow particle size distribution of about 20 nm. X-ray diffraction (XRD) revealed that phase composition and preferable orientation growth of BST depended upon the annealing temperature. Transmission electron microscope (TEM) images showed that the crystallite size of the powders decreased with increasing annealing temperature from 8 nm at 25 °C down to 5 nm at 800 °C. Field emission scanning electron microscope (FE-SEM) analysis and atomic force microscope (AFM) images... 

Nanocrystalline nickel titanate (NiTiO3) thin films and powders with mesoporous structure were produced at the low temperature of 500 °C by a straightforward particulate sol-gel route. The sols were prepared in various Ni:Ti molar ratios. X-ray diffraction and Fourier transform infrared spectroscopy revealed that the powders contained mixtures of the NiTiO 3 and NiO phases, as well as the anatase-TiO2 and the rutile-TiO2 depending on the annealing temperature and Ni:Ti molar ratio. Moreover, it was found that Ni:Ti molar ratio influences the preferable orientation growth of the nickel titanate, being on (202) planes for the nickel dominant powders (Ni:Ti ≥ 75:25) and on (104) planes for the... 

Nanocrystalline neodymium titanium oxide thin films and powders with different phase compositions with mesoporous structure were produced by a straightforward particulate sol-gel route. The sols were prepared in various Nd:Ti molar ratios and they showed a narrow particle size distribution in the range 20-26 nm. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that the powders contained mixtures of Nd4Ti9O24, Nd2Ti4O11, Nd3Ti4O12 for titanium dominant powders (Nd:Ti ≤ 45:60), mixtures of Nd2TiO5 and Nd2O3 for neodymium dominant powders (Nd:Ti ≥ 75:25) and pure Nd3Ti4O12 phase for equal molar ratio of Nd:Ti, depending on the annealing temperature and Nd:Ti... 

Low temperature lithium titanate compounds (i.e., Li4Ti 5O12 and Li2TiO3) with nanocrystalline and mesoporous structure were prepared by a straightforward aqueous particulate sol-gel route. The effect of Li:Ti molar ratio was studied on crystallisation behaviour of lithium titanates. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that the powders were crystallised at the low temperature of 500 °C and the short annealing time of 1 h. Moreover, it was found that Li:Ti molar ratio and annealing temperature influence the preferable orientation growth of the lithium titanate compounds. Transmission electron microscope (TEM) images showed that the average... 

Nanocrystalline zinc titanate (ZnTiO3) thin films and powders with purity of 94% were produced at the low sintering temperature of 500 °C and the short sintering time of 1 h by a straightforward aqueous particulate sol-gel route. The effect of Zn:Ti molar ratio was studied on the crystallisation behaviour of zinc titanates. The prepared sols showed a narrow particle size distribution in the range 17-19 nm. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that the powders contained mixtures of the rhombohedral-ZnTiO3, cubic-ZnO, cubic-Zn2TiO4 phases, as well as the anatase-TiO2 and the rutile-TiO2 depending on the sintering temperature and Zn:Ti molar ratio....