KTaO3 powders and thin films prepared by polymeric precursor method

This work presents perovskite-type KTaO3 powders and thin films synthesis, using a low-cost route based on Pechini method. Powders and films were studied by X-ray diffraction, energy dispersive spectroscopy and scanning electron microscopy. Pyrochlore-free samples are achieved at moderate temperatures (650 °C). Nevertheless, it was verified that with temperature increasing, a small amount of secondary perovskite phases, presenting lowered lattice parameters, is formed in powders. These phases are attributed to stoichiometric deviation due to K losses during thermal treatment. The EDS results support this hypothesis. The microstructure of a sample annealed at 625 °C was studied by X-ray line-broadening analysis. The sample contains a negligible amount of structural distortions and the crystallites are on average isotropic. Concerning KTaO3 films, it was observed that substrates play an important role. While the films prepared onto sintered alumina substrates present pyrochlore contamination, films prepared onto (100) SrTiO3 and (100) LaAlO3 are single phased (only perovskite phase is present) and highly oriented. KTaO3 is epitaxial onto (100) SrTiO3 and textured onto (100) LaAlO3. Moreover, films are crack-free and homogeneous. Refractive indexes, measured by ellipsometry, are about 1.95 and the film thickness is in the range of 130 nm per layer.

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