Texture and phase analysis of a Ca3Co4O9∕Si (100) thermoelectric film

This paper reports the texture analysis as well as the identification of two crystalline phases between a thin film of monoclinic Ca3Co4O9 and a cubic (100) Si substrate, using a diffractometer equipped with a two-dimensional area detector. No reflections other than 00ℓ were observed in the symmetric configuration using an x-ray powder diffraction scan (Bragg-Brentano geometry). Pole figures collected for six reflections using asymmetric configurations did not show ab-plane epitaxial relationships between the film and the substrate. These results establish the Ca3Co4O9 fiber texture of the film with the (001) pole parallel to the surface normal. Single-crystal-like second phases, CaCoSi2O6 and CoO, presumably the interface reaction products of Ca3Co4O9 with the substrate Si, were identified. The near four-fold symmetry and the similar intensity displayed by the 220 reflection from the CaCoSi2O6 structure indicated an epitaxial relation between CaCoSi2O6 and Si, with four symmetry-induced variants being generated with approximately equal volume fractions.