During the last decade a number of ceramic materials, mostly oxides have been suggested as new thermal barrier coating (TBC) materials. These new compositions have to compete with the state-of-the-art TBC material yttria stabilized zirconia (YSZ) which turns out to be difficult due to its unique properties. On the other hand YSZ has certain shortcomings especially its limited temperature capability above 1200 °C which necessitate its substitution in advanced gas turbines. In the paper an overview is tried on the different new materials covering especially doped zirconia, pyrochlores, perovskites, and aluminates. Literature results and also results from our own investigations will be presented and compared to the requirements. Finally, the double layer concept, a method to overcome the limited toughness of new TBC materials, will be discussed.

There is an enormous potential in applying conjugated polymers in novel organic opto-electronic devices such as light emitting diodes and solar cells. Although prototypes and first products exist, a comprehensive understanding of the fundamental processes and energetics involved during photoexcitation is still lacking and limits further device optimisations. Here we report on a unique analysis of the excited states involved in charge generation by photoexcitation. On the model system poly(3-hexylthiophene) (P3HT), we demonstrate the general applicability of our novel approach. From photoemission spectroscopy of occupied and unoccupied states we determine the transport gap to 2.6 eV, which we show to be in agreement with the onset of photoconductivity by spectrally resolved photocurrent measurements. For photogenerated singlet exciton at the absorption edge, 0.7 eV of excess energy are required to overcome the binding energy; the intermediate charge transfer state is situated only 0.3 eV above the singlet exciton. Our results give direct evidence of energy levels involved in the photogeneration and charge transport within conjugated polymers.

Processing of Gd 2 Zr 2 O 7 by atmospheric plasma spraying (APS) is challenging due to the difference in vapor pressure between gadolinia and zirconia. Gadolinia is volatilized to a greater extent than zirconia and the coating composition unfavorably deviates from the initial stoichiometry. Aiming at stoichiometric coatings, APS experiments were performed with a TriplexPro TM plasma torch at different current levels. Particle diagnostics proved to be an effective tool for the detection of potential degrees of evaporation via particle temperature measurements at these varied current levels. Optimized spray parameters for Gd 2 Zr 2 O 7 in terms of porosity and stoichiometry were used to produce double-layer TBCs with an underlying yttria-stabilized zirconia (7YSZ) layer. For comparison, double layers were also deposited with relatively high torch currents during Gd 2 Zr 2 O 7 deposition, which led to a considerable amount of evaporation and relatively low porosities. These coatings were tested in thermal cycling rigs at 1400°C surface temperature. Double layers manufactured with optimized Gd 2 Zr 2 O 7 spray parameters revealed very good thermal cycling performance in comparison to standard 7YSZ coatings, whereas the others showed early failures. Furthermore, different failure modes were observed; coatings with long lifetime failed due to TGO growth, while the coatings displaying early failures spalled through crack propagation in the upper part of the 7YSZ layer.

Perovskite-type SrZrO 3 was investigated as an alternative to yttria-stabilized zirconia (YSZ) material for thermal barrier coating (TBC) applications. Three phase transformations (orthorhombic2pseudo-tetragonal2tetragonal2cubic) were found only by heat capacity measurement, whereas the phase transformation from orthorhombic to pseudo-tetragonal was found in thermal expansion measurements. The thermal expansion coefficients (TECs) of SrZrO 3 coatings were at least 4.5% larger than YSZ coatings up to 12001C. Mechanical properties (Young's modulus, hardness, and fracture toughness) of dense SrZrO 3 showed lower Young's modulus, hardness, and comparable fracture toughness with respect to YSZ. The ''steadystate'' sintering rate of a SrZrO 3 coating at 12001C was 1.04 Â 10 À9 s À1 , which was less than half that of YSZ coating at 12001C. Plasma-sprayed coatings were produced and characterized. Thermal cycling with a gas burner showed that at operating temperatures B12501C the cycling lifetime of SrZrO 3 /YSZ double-layer coating (DLC) was more than twice as long as SrZrO 3 coating and comparable to YSZ coating. However, at operating temperatures 413001C, the cycling lifetime of SrZrO 3 /YSZ DLC was comparable to the optimized YSZ coating, indicating SrZrO 3 might be a promising material for TBC applications at higher temperatures compared with YSZ.

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