Influence of Phase Transformations on Mechanical Properties of Novel Ceramics for Solid Oxide Fuel Cell Anode Applications

Mechanical properties and phase stability of reoxidation-stable anode materials are reported. Elastic moduli of Sr0.895Y0.07TiO3−δ and La0.20Sr0.25Ca0.45TiO3 are characterized from room temperature up to typical operation temperatures. Anomalies in the elastic moduli are followed by X-ray diffraction investigations. The SYT crystal structure is confirmed to change reversibly from pseudo-tetragonal to cubic symmetry at ~200 °C under reducing conditions, leading to a local maximum in the elastic modulus at ~270 °C. The phase transition temperature decreases for SYT exposed to air. The elastic modulus of LSCT reveals two local minima at ~310 °C and ~740 °C. The XRD study confirms pseudo-tetragonal 1→ pseudo-tetragonal 2→ cubic transition sequence at ~300 °C and ~700 °C, respectively, with an anomalous reverse of the crystal lattice parameters during the pseudo-tetragonal 1→ pseudo-tetragonal 2 transition

Investigation of Rhombohedral-Cubic Phase Transition of La0.58Sr0.4Co0.2Fe0.8O3-δ Using HighTtemperature XRD

The phase transition of the La0.58Sr0.4Co0.2Fe0.8O3-δ oxygen transport membrane material has been investigated by X-ray diffraction at elevated temperatures. It has a rhombohedral symmetry at room temperature that transforms to a cubic symmetry at operation relevant higher temperatures, which was investigated in detail in the current work on the basis of bar type and powder specimens and discussed in terms of correlations with mechanical behavior

Influence of deposition conditions and substrate morphology on the electrical properties of sputtered ZnO:Al grown on texture-etched glass

The focus of this work is the growth of aluminum-doped zinc oxide (ZnO:Al) on texture-etched glass substrates. We investigated the influence of sputter parameters, pressure and temperature on the charge carrier mobility of ZnO:Al films grown on different substrate textures. An optimized sputtering process was developed which led to charge carrier mobilities on textured substrates that are close to those on flat substrates. Based on X-ray diffraction measurements, we qualitatively explain the effect of different sputtering conditions. Furthermore, the ZnO:Al charge carrier mobility was related to the substrate morphology. ZnO:Al films on U-shaped surface morphologies showed significantly higher charge carrier mobilities than those on V-shaped structures. ZnO:Al damp heat stability and etching behavior provided evidence that the number of ZnO:Al growth disturbances on textured substrates can be reduced by adequate substrate morphology and sputtering conditions

Investigation of Vaporization of alkali Metals From Solidified Gasifier Slags by Knudsen Effusion Mass Spectrometry

One problem in coal gasification is the release of alkali species, which can cause fouling and corrosion. Depending on their composition, slags have a high potential for alkali retention. Therefore, the vapor pressures of alkali species (Na, K) over four real solidified gasifier slag samples were determined over the temperature range 1134 to 1591 K by Knudsen effusion mass spectrometry (KEMS). In addition, the residues from the KEMS investigations were studied by X-ray diffraction (XRD) and scanning electron microscope/energy dispersive X-ray (SEM/EDX) to determine the phase composition of the samples and map the alkali distribution. A strong correlation between the composition of the slags in terms of amount of acidic oxides (SiO2, Al2O3) and basic oxides (CaO, FeO) and the volatility was determined. The volatility results showed that higher acidic oxide content leads to higher alkali retention capability. The XRD and SEM/EDX analysis of the KEMS residues showed that an anorthite type phase contains more Na than all the other phases in the equilibrium

Increasing Fracture Toughness and Transmittance of Transparent Ceramics using Functional Low-Thermal Expansion Coatings

Transparent polycrystalline ceramics have the potential to enable applications no other materials can, but to do so their strength and toughness must be improved. However, surface strengthening treatments like those used for glasses have so far remained elusive. Here for the first time, we report on engineering unprecedented surface compression, of the magnitude achieved for ion-exchange strengthened glasses (~750 MPa) in transparent ceramics. This was achieved by applying functional, low thermal-expansion yttria coatings onto yttria-stabilized zirconia substrates and thermally treating. In some instances, the treatment more than doubled the fracture toughness while simultaneously increasing light transmittance

XRD analysis of strain states in epitaxial YSZ/RE2O3 (RE=Y, Er) multilayers as a function of layer thickness

The strain in epitaxialmultilayerswith coherent interfaces between yttria stabilized zirconia and rare earth metaloxides is investigated as a function of the layer thickness. An analyticmodel was developed to describe the strain,which is analyzed bymeasuring distinct XRD reflections in two orientations. Applying our model to this data theinterface thickness δ0 is estimated. For Y2O3/YSZ multilayers δ0 is 9.3 nm and for Er2O3/YSZ multilayers δ0 is8.2 nm. Our findings are in accordance with the assumption that mismatch induced stress can be relaxed byelastic deformatio

Sr-Diffusion in Ce0.8Gd0.2O2-δ Layers for SOFC Application

ABSTRACTIn this study Sr2+ diffusion along Ce0.8Gd0.2O2-δ (CGO) grain boundaries is investigated. Model samples with different grain boundary densities were prepared by different thin film tech-niques. Diffusion experiments were performed by annealing and subsequent ToF-SIMS analysis. The activation energy of grain boundary diffusion is determined as 492 kJ/mol, which is 2/3 of the bulk diffusion activation energy 739 kJ/mol, deduced from literature data [1-5].The formation of an electrical blocking SrZrO3 layer due to grain boundary diffusion of Sr2+ through a CGO barrier layer may limit the long term stability of Solid Oxide Fuel Cells based on Zr0.85Y0.15O2-δ electrolytes and La0.58Sr0.4Co0.2Fe0.8O3-δ cathodes. The grain boundary diffusivity and the CGO grain boundary density highly influence the kinetic of the SrZrO3 formation. Aim of this study is to gain data for a prediction of the maximum lifetime of a SOFC system, limited by the increasing cell resistivity due to SrZrO3 formation. Specifications for the CGO barrier layer preparation concerning grain boundary density are determined.</jats:p