Interpretation of the optical absorption spectrum of Co3O4 with normal spinel structure from first principles calculations

First principles calculations based on density functional theory have been employed to study the electronic, magnetic and optical properties of Co₃O₄ in a cubic normal spinel structure. Exchange and correlation effects between electrons were treated by a B3PW91 hybrid functional, which produced better results than others scheme, such as GGA+U or PBE0 hybrid functionals or mBJ semilocal potential. The work focuses on clarifying the nature of the optical absorption bands, which have motivated various theoretical and experimental works in the literature. The calculated optical absorption spectrum was compared with available experimental data. On the basis of this calculated electronic and magnetic structure, the optical absorption peaks (theoretical and experimental) could be satisfactorily explained in terms of d3d   charge transfer transitions between both CO²⁺${\mathrm{CO}}^{2^{+}}$→CO²⁺${\mathrm{CO}}^{2^{+}}$ and CO³⁺${\mathrm{CO}}^{3^{+}}$→CO³⁺${\mathrm{CO}}^{3^{+}}$ ions. The calculations also predicted that the crystal field splittings at both octahedral and tetrahedral sites in the Co₃O₄ compound are of the same magnitude.     

Variational formulation of the equivalent eigenstrain method with an application to a problem with radial eigenstrains

In this paper a variational formulation of the equivalent eigenstrain method is established. A functional of the Hashin–Shtrikman type is proposed such that the solution of the equivalent eigenstrain equation is a unique minimizer of the functional. Moreover, it is also shown that the equivalent eigenstrain equation is the Euler–Lagrange equation of the potential energy of the inclusions. An approximate solution of the equivalent eigenstrain equation is then found as a minimizer of the functional on a finite dimensional span of basic eigenstrains. Special attention is paid to possible symmetries of the problem. The variational formulation is illustrated by determination of effective linear elastic properties. In particular, material with a simple cubic microstructure is considered in detail. A solution for the polynomial radial basic eigenstrains approximation is found. In particular, for the homogeneous eigenstrain approximation, the effective moduli are derived in an exact closed form.     

Surface morphology, growth rate and quality of diamond films synthesized in hot filament CVD system under various methane concentrations

Hot filament chemical vapor deposition (CVD) technique has been used to deposit diamond films on silicon substrate. In the present study, diamond films were grown at various vol.% CH₄ in H₂ from 0.5% to 3.5%, at substrate temperature and pressure of 850 °C and 80 torr, respectively. Scanning electron microscopy, X-ray diffraction and Raman spectroscopy were employed to analyze the properties of deposited films. The formation of methyl radicals as a function of vol.% CH₄ not only changes film morphology but also increase film growth rate. At low, intermediate and high vol.% CH₄, cluster, faceted cubes and pyramidal features growth, were dominant. By increasing vol.% CH₄ from 0.5% to 3.5%, as the growth rate improved from ∼0.25 μm/h to ∼2.0 μm/h. Raman studies features revealed high purity diamond films at intermediate range of vol.% CH₄ and grain density increased by increasing CH₄ concentration. The present study represents experimentally surface morphology, growth rate and quality of diamond films grown in hot filament CVD system at various CH₄ concentrations.     

Tripolyphosphate-responsive release property of monoolein cubic phase containing sodium dodecyl sulfate and oligo chitosan

Tripolyphosphate (TPP)-responsive MO cubic phase was prepared by immobilizing oligo chitosan in the water channel through its electrostatic attraction with sodium dodecyl sulfate (SDS). The phase transition temperature (PTT) increased with increasing the content of SDS. The PTT of cubic phase whose SDS content was 0%, 0.21%, 0.42%, 0.84%, and 1.68%, determined by polarized microscopy, was about 69.5°C, 72°C, 75°C, 80.5°C, and 95°C, respectively. The PTT did not markedly deviate from that determined by differential scanning calorimetry. The release degree for 72 h of dye (i.e., amaranth and methylene blue) was dependent on the pH value of release medium (pH 3.0 and pH 7.0). Moreover, the release degree significantly increased when the TPP concentration in the release medium increased to 0.4% (w/v). Oligo chitosan was electrostatically complexed with TPP and the complexation took place extensively at the oligo chitosan/TTP mass ratio of 1:0.125 and 1:0.25 and at the oligo chitosan concentration of 1.6% (w/v), evidenced by optical spectroscopy and scanning electron microscopy. It was thought that the complexation was responsible for the TPP concentration-dependent release.