Mixed-valence Ln1-xMxCoO3 (cobaltate) and Ln1-xMxMnO3 (magnate) perovskites have many interesting properties such as high electric conductivity, magnetism and ionic conductivity. Applications may be found in catalysts, oxygen permeation membranes, electrode materials for high-temperature devices, ceramic conductors for piezoelectric films, collosal magnetic resistance (CMR) sensor films in bolometers and recording devices. The dominating deposition techniques for such materials today are high vacuum pulsed laser deposition (PLD) and sputtering, which are difficult to apply to large substrates and complex shape substrates. Sol-gel methods on the other hand represent versatile and fast routes to industry-scale production and are less restricted regarding substrate size and shape.
Here we describe all-alkoxide routes to various polycrystalline and epitaxial cobaltate and manganite films and nano-phase powders with up to four metal constituents including; Ln1-xMxMnO3 (Ln=La, Nd; M=Ca, Sr, Ba) and La0.5Sr0.5CoO3. The conversion of gel to perovskite has been studied in detail with a combination of TGA, DSC, TEM-EDS, SEM, XRD and IR spectroscopy for all systems. This allowed us to obtain the perovskite crystallization temperature and the effect of different heating programs to the phase development and quality of the perovskite films and powders obtained. For instance it was found that very slow heating or annealing at low temperatures could be used to obtain perovskites at very low temperatures, but such perovskites were A-site inhomogeneous on a nano-level which alters their properties. This is an effect likely to apply also to other solution based synthesis routes. Pure A-site homogeneous perovskites were typically obtained at around 700oC. Comparison of e.g. La0.67Ca0.33MnO3 films made from alkoxides with films from PLD showed that they had equal quality with respect to expitaxial alignment and colossal magneto resistance. Highly epitaxial films with a tensile stress in the c-direction and compressive strain in the a,b direction were also prepared of La0.5Sr0.5CoO3, as well as polycrystalline films on different substrates such as SiO2 and Pt/TiO2/SiO2/Si.
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