Structural and magnetic properties of nanosized barium hexaferrite powders obtained by microemulsion technique

peer reviewe

Degradation of anode supported cell (ASC) performance by Cr-poisoning

Performance and stability of solid oxide fuel cells (SOFC) have been continuously improved at the single-cell level. Connecting the individual cells by a metallic interconnector (MIC) in a stack, though, yields remarkable losses in performance and leads to an enhanced degradation. These effects are attributed to, inter alia, Cr evaporation from the MIC and, thus, Cr poisoning of the cathode.To determine the degradation rate caused by Cr poisoning, this paper focuses on the differences in single cell performance and short-term stability by using either an inert flowfielcl or a flowfield made of a chromia-forming alloy. To provide a homogeneous current collection and gas distribution over the complete cathode area and to avoid a direct contact between MIC made of Crofer22APU and LSM, a platinum mesh was used as current collector. The cell performance was evaluated by analyzing its current-voltage characteristics and using electrochemical impedance spectroscopy.A detailed analysis of impedance spectra by the distribution of relaxation times (DRT) and a subsequent Complex Nonlinear Least Squares (CLNS) fit facilitated the separation of anodic and cathodic polarization processes. In the presence of a chromia-forming alloy the polarization resistance of the cathode showed a significantly higher initial value (+64 m Omega.cm(2)) than without and a high degradation rate of 213 mu Omega.cm(2) h(-1) during 280 h of galvanostatic operation at 800 degrees C. (C) 2010 Elsevier B.V. All rights reserved

XPS study of Au/GaN and Pt/GaN contacts

36 hlm. : ilus. ; tab. ; 29 cm

XPS study of Au/GaN and Pt/GaN contacts

Au/GaN and Pt/GaN contacts have been studied with XPS. According to XPS depth profiling, the N signal is weak in the region below the metal contact and the Pt or Au signal decreases much more slowly than expected for a sharp interface. Next, we have performed in situ studies of the formation of Au contacts on GaN. In contrast to the results from depth profiling, we observe 2D growth and little or no chemical interaction between Au and GaN. This suggests that conventional calculations of sputtering yields and ion-beam-induced mixing cannot be applied to the analysis of noble metal/GaN depth profiles. Heating during or after Au deposition results in strong clustering, observed by both XPS and AFM. The Schottky barrier height measured by XPS is 1.15 eV.</jats:p