Role of lattice strain and defect chemistry on the oxygen vacancy migration at the (8.3%Y2O3-ZRO2)/SrTiO3 hetero-interface: A first principles study

We report on the mechanism and the upper limits in the increase of oxygen ion conductivity at oxide hetero-interfaces, particularly the 8.3%Y2O3-ZrO2/SrTiO3 (YSZ/STO) as a model interface. We consider two factors contributing to the increase in ionic conductivity at or near the interface: 1) a favorable strain state to shift and/or change the symmetry of electron energy levels to provide improved charge transfer and mobility. 2) the alteration of the defect chemistry to enhance the density and distribution of oxygen vacancies. First principles and Kinetic Monte-Carlo simulations were performed to identify the atomic-scale nature of the hetero-interface and the oxygen vacancy migration barriers and diffusivity. Our results suggest that the modulation in both the lattice strain and the defect chemistry due to the YSZ/STO interface can enhance the ionic conductivity in YSZ up to six orders of magnitude by reducing the migration barrier and increasing the oxygen vacancy concentration, respectively

On the Formation and Constitution of Calcium-Ferrite

We studied the formation, constitution, melting point, and micro-structures of Ca-ferrite prepared from the mixtures of CaO and Fe₂O₃ by chemical- and X-ray analyses. Main results obtained are as follows. 1) Ca-ferrite has two kinds of compound which are represented by CaOFe₂O₃ (monocalcium-ferrite) and 2CaOFe₂O₃ (dicalcium-ferrite). 2) CaOFe₂O₃ is formed over 700° and the formation is completed at about 1000℃. 3) When the sample contains excess CaO, 2CaOFe₂O₃ is formed over 1000℃ by the reaction of CaOFe₂O₃ and excess CaO and this reaction is completed at about 1200℃. 4) CaOFe₂O₃ dissolves Fe₂O₃ at high temperature and the sample containing 60 mol% of Fe₂O₃ shows single phase at 1200℃. 5) The compound represented by 3CaOFe₂O₃ or CaO2Fe₂O₃ cannot be observed by X-ray examination ; the former is nothing but a mixture of CaO and 2CaOFe₂O₃, and the latter, simply a mixture of solid solution of CaOFe₂O₃ and Fe₂O₃ and free Fe₂O₃. 6) CaOFe₂O₃ melts at 1220° and is dissolved in hot 1 : 1 HCl by heating while 2CaOFe₂O₃ melts at 1280C° and is dissolved immediately in cold dil HCl, and they both have paramagnetic property. 7) CaOFe₂O₃ forms fine hexagonal crystals near its melting point and shows growth steps, but 2CaOFe₂O₃ is apt to become glassy and its definite crystal forms are difficult to recognize under microscope

Interstitialcy diffusion of oxygen in tetragonal La₂CoO_4+δ

We report on the mechanism and energy barrier for oxygen diffusion in tetragonal La2CoO4+δ. The first principles-based calculations in the Density Functional Theory (DFT) formalism were performed to precisely describe the dominant migration paths for the interstitial oxygen atom in La2CoO4+δ. Atomistic simulations using molecular dynamics (MD) were performed to quantify the temperature dependent collective diffusivity, and to enable a comparison of the diffusion barriers found from the force field-based simulations to those obtained from the first principles-based calculations. Both techniques consistently predict that oxygen migrates dominantly via an interstitialcy mechanism. The single interstitialcy migration path involves the removal of an apical lattice oxygen atom out from the LaO-plane and placing it into the nearest available interstitial site, whilst the original interstitial replaces the displaced apical oxygen on the LaO-plane. The facile migration of the interstitial oxygen in this path is enabled by the cooperative titling-untilting of the CoO6 octahedron. DFT calculations indicate that this process has an activation energy significantly lower than that of the direct interstitial site exchange mechanism. For 800-1000 K, the MD diffusivities are consistent with the available experimental data within one order of magnitude. The DFT- and the MD-predictions suggest that the diffusion barrier for the interstitialcy mechanism is within 0.31-0.80 eV. The identified migration path, activation energies and diffusivities, and the associated uncertainties are discussed in the context of the previous experimental and theoretical results from the related Ruddlesden-Popper structures

Preparation of Titanium Tetrachloride : Some Experiments for the Determination of its Mechanism

As one of the fundamental experiments on the preparation of titanium tetrachloride, several chlorinations such as that with and without carbon by chlorine gas, that by the mixed gas of chlorine and carbon monoxide, and that by carbon tetrachloride vapour are examined using titanium dioxide and its lower oxides as the material. By the results, it is known that the ignition temperature generally becomes lower as the titanium content in the oxides increases, but it is exceptional in case of the chlorination by the mixed gas of chlorine and carbon monoxide

On the Formation and Constitution of Nickel-Ferrite

The authors have studied on the formation, constiution, magnetic properties, and microstructures of Ni-ferrite, and also prepared the single crystals of Ni-ferrite. The intimate mixtures of NiO and Fe₂O₃ powder of various molar ratio were used as raw materials. The samples were heated at various temperature and were investigated by X-ray and magnetic analyses. The main results obtained were as follows. 1) Ni-ferrite is formed from oxides mixture at above 675℃. 2) NiFe₂O₄ dissolves excess NiO and Fe₂O₃ at above 1250° and 1200℃ respectively. At 1300°, the single spinel phase is obtained in the range of Fe₂O₃ content of from 52% to 86.5% in weight. 3) Ni-ferrite which dissolves excess Fe₂O₃ precipitate free Fe₂O₃ by annealing at 700℃ for 3 hours. 4) Ni-ferrite is a ferromagnetic compound and the intensity of magnetization shows a sharp maximum at the 1-2 sample at above 1200℃. The magnetism of the samples containing excess Fe₂O₃ are weakend remarkably by annealing at above 500℃, and this phenomena seems to be connected with precipitation of excess Fe₂O₃. 5) The growth steps are recognized on the crystals which developes on the sintered surface of Ni-ferrite. 6) The lattice constant of Ni-ferrite is about 8.22~8.23Å, and Curie point is about 588℃. 7) Ni-ferrite single crystal forms regular octahedron