Kationendiffusion in Cer(IV)-Oxid

The migration of cerium ions in CeO$_2$ was theoretically investigated by means of static lattice simulations. Vacancy, interstitial and interstitialcy mechanisms were modelled by means of quantum-mechanical simulations employing density functional theory and classical simulations based on various sets of empirical pair parameters in order to determine the respective activation enthalpies of migration. Defect chemical modelling was employed to calculate defect concentrations, defect generation enthalpies, bulk diffusion coefficients $D^b$ and enthalpies of diffusion $\Delta H_{D^b}$ in the temperature range of 1330 K $\leq T \leq$ 2000 K at an oxygen partial pressure of $p$O$_2$ = 0.21 bar for acceptor dopant fractions of $2·10^{-4}$ mol/mol oxide and 0.1 mol/mol oxide. Although the lowest migration enthalpies were found for the interstitialcy mechanism and the vacancy mechanism along $\langle$110$\rangle$, the highest diffusion coefficients were obtained for the vacancy mechanism for both dopant site fractions. The results emphasize that the concentrations of the defects, as a function of dopant level and temperature, also responsible for diffusion have to be considered to predict the predominant cation diffusion mechanism rather than solely relying on the migration enthalpy. The lowest enthalpy of diffusion was derived to be $\Delta H_{D^b}(V_{Ce}^{''''})=$ 8.44 eV for the vacancy mechanism along $\langle$110$\rangle$ and an acceptor dopant fraction of $2·10^{-4}$ mol/mol oxide in the considered temperature regime. In addition, the diffusion behaviour of Hf and Zr into Gd-doped CeO$_2$ specimens were probed by diffusion experiments. Thin films of (Hf,Zr)O$_2$ were deposited by means of pulsed laser deposition onto dense, polycrystalline, thermally equilibrated Gd-doped CeO$_2$ ceramics with a gadolinium dopant site fraction of $n_{G^d}$ = 0.5%. High temperature anneals in the range of 1420 K $\leq T \leq$ 1600 K in ambient air were employed to probe the diffusion of Hf and Zr. The specimens were analysed by means of Time-of-flight Secondary Ion Mass Spectrometry (ToF-SIMS) and the obtained depth profiles of Hf and Zr yielded two features for both cations. The first feature was attributed to bulk diffusion, the derived isothermal bulk diffusion coefficients, $D^b$, and the activation enthalpies of bulk diffusion $\Delta H_{D^b}$ were similar for the two impurity cations, $\Delta H_{D^b}$(Zr) = (5.5 $\pm$ 0.4) eV and $\Delta H_{D^b}$(Hf) = (5.3 $\pm$ 0.3) eV. The second feature was attributed to fast grain-boundary diffusion according to Harrison Type B kinetics. Grain-boundary diffusion products, $\omega D^{gb}$, could only be derived for Hf because an unintended pollution of the polycrystals by Zr during the preparation routine prevented the evaluation of the respective grain-boundary profile. The derived grain-boundary diffusion coefficients $D^{gb}$(Hf) were three to four orders of magnitude higher than $D^b$(Hf) assuming a grain-boundary width of one nanometer. The activation enthalpy of the grain-boundary diffusion product, $\Delta H_{\omega D^{gb}}$ (Hf) = (5.9 $\pm$ 0.8) eV, is, surprisingly, similar to the activation enthalpies for bulk diffusion. The experimentally derived diffusion coefficients $D^b$ of Hf and Zr were roughly nine orders of magnitude higher and the bulk diffusion enthalpy 3 eV lower than the respective computationally derived values. Various reasons for this discrepancy are discussed. When comparing the two data sets, a complicating factor is the use of Hf and Zr as a replacement for a cerium tracer since the two cations locally alter the defect thermodynamics in CeO$_2$ during diffusion. Agreements and deviations of the results of this work to lower valent impurity cation diffusion studies of ceria based materials with high gadolinium dopants site fractions are presented

Serenade [music] : male voices /

26 (Publisher number). For baritone solo and TTBB.; Cover title.; Pl. no.: 26.; Date approximated from publisher's address on imprint.; Also available online http://nla.gov.au/nla.mus-vn4853658

Concentration and Diffusivity of Oxygen Interstitials in Niobia-Doped Ceria

We studied the behaviour of oxygen interstitials in donor-doped ceria using equilibrium conductivity measurements, conductivity relaxation experiments and (18O2 / 16O2) isotope exchange experiments. Equilibrium conductivities and conductivity relaxation experiments were performed in the oxygen activity range 10-6 ≤ aO2 ≤ 10-1 at temperatures of 923 K, 973 K and 1023 K. Oxygen isotope exchanges were carried out at 673 ≤ T / K ≤ 1073 at an oxygen activity of aO2 = 0.2, and oxygen isotope profiles in the solid were obtained by Secondary Ion Mass Spectrometry (SIMS). Analysis of the measured equilibrium conductivities with a defect-chemical model yielded the incorporation enthalpy and entropy of oxygen interstitials. Values of the chemical diffusion coefficient of oxygen (from relaxation experiments) and of the tracer diffusion coefficient of oxygen (from isotope exchange experiments) were converted into diffusion coefficients of oxygen interstitials using the defect-chemical model. Based on these data, the activation enthalpy of oxygen-interstitial migration in Ce0.99Nb0.01O2+δ was found to be (1.28 ± 0.13) eV. Strong enrichment of Si, Ca and Al at the surfaces of the ceramic samples prevented the determination of surface exchange coefficients that refer to donor-doped ceria

Comparison of Two Solid-Phase Extraction (SPE) Methods for the Identification and Quantification of Porcine Retinal Protein Markers by LC-MS/MS

Proper sample preparation protocols represent a critical step for liquid chromatography-mass spectrometry (LC-MS)-based proteomic study designs and influence the speed, performance and automation of high-throughput data acquisition. The main objective of this study was to compare two commercial solid-phase extraction (SPE)-based sample preparation protocols (comprising SOLAµTM HRP SPE spin plates from Thermo Fisher Scientific and ZIPTIP® C18 pipette tips from Merck Millipore) for analytical performance, reproducibility, and analysis speed. The house swine represents a promising animal model for studying human eye diseases including glaucoma and provides excellent requirements for the qualitative and quantitative MS-based comparison in terms of ocular proteomics. In total six technical replicates of two protein fractions [extracted with 0.1% dodecyl-ß-maltoside (DDM) or 1% trifluoroacetic acid (TFA)] of porcine retinal tissues were subjected to in-gel trypsin digestion and purified with both SPE-based workflows (N = 3) prior to LC-MS analysis. On average, 550 ± 70 proteins (1512 ± 199 peptides) and 305 ± 48 proteins (806 ± 144 peptides) were identified from DDM and TFA protein fractions, respectively, after ZIPTIP® C18 purification, and SOLAµTM workflow resulted in the detection of 513 ± 55 proteins (1347 ± 180 peptides) and 300 ± 33 proteins (722 ± 87 peptides), respectively (FDR < 1%). Venn diagram analysis revealed an average overlap of 65 ± 2% (DDM fraction) and 69 ± 4% (TFA fraction) in protein identifications between both SPE-based methods. Quantitative analysis of 25 glaucoma-related protein markers also showed no significant differences (P > 0.05) regarding protein recovery between both SPE methods. However, only glaucoma-associated marker MECP2 showed a significant (P = 0.02) higher abundance in ZIPTIP®-purified replicates in comparison to SOLAµTM-treated study samples. Nevertheless, this result was not confirmed in the verification experiment using in-gel trypsin digestion of recombinant MECP2 (P = 0.24). In conclusion, both SPE-based purification methods worked equally well in terms of analytical performance and reproducibility, whereas the analysis speed and the semi-automation of the SOLAµTM spin plates workflow is much more convenient in comparison to the ZIPTIP® C18 method