Diffusion coefficients of oxygen in Nd 2CuO 4−δ

The oxygen nonstoichiometry x and the chemical diffusion coefficient of oxygen in Ba2YCu3O7−x were measured by means of thermogravimetry as a function of oxygen partial pressure and temperature over the ranges 102 <Po2/Pa<105and 698<T/K<1173. The oxygen partial pressure dependence of x in Ba2Cu3O7−x obtained in this study was in good agreement with those previously reported by other researchers. The chemical diffusion coefficients of oxygen in Ba2YCu3O7−x with various oxygen nonstoichiometry x=0.063–0.77 were measured, and they increased with decreasing oxygen nonstoichiometry x at constant temperature. The compositional dependence of the chemical diffusion coefficient changed at about x=0.35, indicating the occurrence of the phase transition from the tetragonal to the orthorhombic structure. The activation energies of the chemical diffusion coefficients of oxygen in Ba2YCu3O7−x with various x were observed to be about 115·kJ mol−1, irrespective of oxygen nonstochiometry x. The self-diffusion coefficient of oxygen and the diffusion coefficient of oxygen vacancy were calculated from the chemical diffusion coefficient, and were compared with those of another superconductor La2−ySryCuO4−x.

Relation between chemical surface diffusion coefficient and order of the adsorbate layer

Modeling oxygen diffusion in barium titanate using molecular dynamics: Comparison between Mg and Sc dopants

ABSTRACTExperimental results from electrical conductivity relaxation (ECR) measurements on SrFeO3-x are described. Values of Dchem and kchem were obtained by monitoring the variation of the time dependence of the electrical conductivity after an abrupt change in the oxygen partial pressure. Values for the oxygen ion and vacancy diffusion coefficients were calculated from the measured thermodynamic factors and compared with those of other compositions in the series La1-xSrxFeO3-x. The surface exchange coefficients, kchem and kex were also determined.

Electrochemical investigation of the chemical diffusion, partial ionic conductivities, and other kinetic parameters in Li 3Sb and Li 3Bi

Much recent attention has focused on the voltage-driven reversible topotactic transformation between the ferromagnetic metallic perovskite (P) SrCoO3-δ and oxygen-vacancy-ordered antiferromagnetic insulating brownmillerite (BM) SrCoO2.5. This is emerging as a paradigmatic example of the power of electrochemical gating (using, e.g., ionic liquids/gels), the wide modulation of electronic, magnetic, and optical properties generating clear application potential. SrCoO3 films are challenging with respect to stability, however, and there has been little exploration of alternate compositions. Here, we present the first study of ion-gel-gating-induced P → BM transformations across almost the entire La1-xSrxCoO3 phase diagram (0 ≤ x ≤ 0.70), under both tensile and compressive epitaxial strain. Electronic transport, magnetometry, and operando synchrotron X-ray diffraction establish that voltage-induced P → BM transformations are possible at essentially all x, including x ≤ 0.50, where both P and BM phases are highly stable. Under small compressive strain, the transformation threshold voltage decreases from approximately +2.7 V at x = 0 to negligible at x = 0.70. Both larger compressive strain and tensile strain induce further threshold voltage lowering, particularly at low x. The P → BM threshold voltage is thus tunable, via both composition and strain. At x = 0.50, voltage-controlled ferromagnetism, transport, and optical transmittance are then demonstrated, achieving Curie temperature and resistivity modulations of ∼220 K and at least 5 orders of magnitude, respectively, and enabling estimation of the voltage-dependent Co valence. The results are analyzed in the context of doping- and strain-dependent oxygen vacancy formation energies and diffusion coefficients, establishing that it is thermodynamic factors, not kinetics, that underpin the decrease in the threshold voltage with x, that is, with increasing formal Co valence. These findings substantially advance the practical and mechanistic understanding of this voltage-driven transformation, with fundamental and technological implications.

The growth kinetics of thin anodic WO 3 films investigated by electrochemical impedance spectroscopy

Oxygen permeation rates are reported for 2 mm thick La1-xSrxCoO3-δ(0 ≤x≤0.8) in the temperature range 700 ≤T1100 °C and oxygen partial pressure range 7.0 x 103- 1.0 x 105Pa. With the exception ofx= 0.6 permeation rates increase with an increase in Sr doping level. The oxygen permeation can be described by Wagner theory. An anomaly is observed in the oxygen permeation between 750 - 775 °C, which is attributed to an order-disorder transition. It is further shown that the partial pressure at the low partial pressure side of the membrane has an important influence on the permeation rate. The (calculated) ionic conductivities and oxygen vacancy diffusion coefficients are among the highest reported in literature.

Measurement of reduction kinetics in Nb 2O 5-doped SrTiO 3 by use of a new technique of liquid film migration

Modeling of conductivity relaxation in oxide ceramics taking account of concentration dependent chemical diffusivities and surface exchange coefficients

The binding of two simple tripeptides, glycyl-histidyl-glycine (GHG) and phenylalanyl-histidyl-phenylalanine (FHF) with SDS micelles was examined using (1)H NMR chemical shift analysis and self-diffusion coefficients measured with pulsed-field gradient NMR spectroscopy. The presence of GHG or FHF did not appear to significantly affect the critical micelle concentration (cmc) or the average size of the SDS micelles formed. The chemical shifts of several of the GHG resonances change as a function of SDS concentration, indicating an interaction between the peptide and the micelles. In addition, the concentration-dependent decrease observed for the GHG diffusion coefficients suggests association of the peptide with SDS micelles. The free and micelle-associated GHG are in fast exchange on both the (1)H chemical shift and diffusion time scales. The equilibrium constant for the binding of GHG to SDS micelles was determined from the analysis of the concentration dependence of the histidine C2 and C4 resonances to be 17 ± 5 and 24 ± 6 M(-)(1), respectively. The precision of the equilibrium constants obtained by analysis of the chemical shift data is limited by the small chemical shift changes observed. Analysis of the concentration dependence of the diffusion coefficients produced an equilibrium constant of 17 ± 1 M(-)(1). The more hydrophobic peptide, FHF is strongly associated with the SDS micelles. Because the fraction of free FHF is small in these solutions, it was not possible to determine a formation constant for the interaction of FHF with the SDS micelles by analysis of either the (1)H chemical shift or diffusion coefficient data. The cmc of SDS in 0.10 M Na(2)C(2)O(4) buffer was determined to be 5.4 ± 0.1 mM by analysis of the SDS diffusion coefficients in the absence of the peptides. The SDS cmc could also be extracted from the GHG and FHF diffusion coefficients measured as a function of the SDS concentration. The cmc determined from the GHG diffusion data, 5.7 ± 0.2 mM, is in good agreement with the value determined from analysis of the SDS diffusion coefficients in the 5.0 mM GHG solution, 5.2 ± 0.1 mM. The smaller cmc determined from the FHF diffusion data, 4.1 ± 0.1 mM, may reflect some association of the SDS with the peptide prior to micelle formation in bulk solution.

Mass transport in cuprous oxide

La2Mo2O9-based oxide-ion conductors have attracted more and more attention since the high ionic conductivity was reported in 2000 by Lacorre et al. in this kind of material. In this paper the recent investigation on the novel La2Mo2O9-based oxide-ion conductors is reviewed. It is focused on the structure and phase transition, oxide-ion conductivity, mechanism of oxygen vacancy diffusion, chemical stability and thermal expansion coefficient in the pure and doped La2Mo2O9 samples. It is pointed out that the La2Mo2O9-based oxide-ion conductors could be possibly applied in the fields such as solid oxide fuel cells, oxygen sensors and oxygen permeable membranes.

Self-diffusion and collective diffusion of hydrogen in TaH x

Chemical diffusion and defect mobility in nonstoichiometric manganous sulfide