0.3 MnO 3 . Chemical analysis revealed considerable interdiffusion between the primary phases as well as A-site deficiency of LaMnO 3 and La 0.7 Sr 0.3 MnO 3 when exposed to cubic zirconia. The oxidative/reductive nature of the chemical reaction between strontiumsubstituted lanthanum manganite and yttria-stabilized zirconia is discussed in relation to the Sr content in LSM. The lattice parameter of cubic zirconia was observed to be quite sensitive to the interdiffusion and is an excellent tool for investigating reactions on heterophase interfaces involving stabilized zirconia.

Formation of secondary phases and diffusion of cations in diffusion couples of yttria-stabilized zirconia and lanthanum manganite substituted with 0 to 60 mol% strontium have been studied by scanning electron microscopy and energy dispersive X-ray spectroscopy. Only the primary phases were observed after 120 h at 1200°C, while formation of secondary phases was identified already after 1 h heat treatment at 1350°C. The phase composition of the reaction layer altered from La 2 Zr 2 O 7 to SrZrO 3 at increasing Sr content in La x Sr 1−x MnO 3 . The thickness of the reaction layer was increasing with heat treatment time. In diffusion couples of La 0.4 Sr 0.6 MnO 3 formation of manganese oxide was observed in the perovskite layer after 1 h heat treatment at 1350°C, while isolated grains of SrZrO 3 relatively deep inside the zirconia were observed after longer heat treatment time. Diffusion of Mn into zirconia was observed preferenced along grain boundaries in the early stage of the interface reaction.

Mechanical stress-strain behavior of LaCoO 3 , La 0.8 Ca 0.2 CoO 3 , and La 0.7 Ca 0.3 CoO 3 was studied under compression at 251 and 3001C. A hysteresis in the stress-strain relationship due to reorientation of ferroelastic domains (deformation twins) was observed, and a remanent strain is measured after unloading. The cohersive stress, defined as the maximum in effective elastic compliance during first loading, increases with substitution of Ca for La and decreases with increasing temperature. Domain reorientation was confirmed by X-ray diffraction of surfaces parallel and perpendicular to the loading direction. LaCoO 3 can be regarded as a soft ferroelastic material while the 30% Casubstituted material is a hard ferroelastic. The hysteresis of the stress-strain relationship was clearly dependent on both composition and temperature. J ournal

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The reaction between Ca- and Sr-substituted LaCoO3 and CaSiO3/Ca2SiO4 has been studied by electron microscopy (SEM and TEM) and X-ray diffraction. The aim was to investigate the chemical stability of these materials as a model system for, respectively, a membrane and a sealing material in dense oxygen-permeable membrane systems. Sintered powder mixtures of the two materials were analyzed to gain information about coexistent phases in the CaO/SrO−La2O3 -CoO−SiO2 system. The estimated phase composition along the CaSiO3 -LaCoO3 line has been worked out. The chemical aspects of glass−ceramic sealing of dense perovskite membranes were studied by making diffusion couples. LaCoO3 was found to be kinetically more stable to calcium silicate than Ca- and Sr-substituted LaCoO3. The results also revealed that Ca2SiO4 is a more suitable sealing material than CaSiO3, due to lower reactivity. Thus, the stability of the membrane/sealant interface was observed to be quite sensitive to the O:Si ratio of the calcium silicate:  3 < O:Si < 4 will give rise to good sealing properties and moderate reactivity to the membrane material. A suitable material is a two-phase material with O:Si close to four, e.g. an orthosilicate glass−ceramic material with small amounts of metasilicate or disilicate glass.