Texture and phase analysis of a Ca3 Co4 O9 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 Ca3 Co4 O9 and a cubic (100) Si substrate, using a diffractometer equipped with a two-dimensional area detector. No reflections other than 00 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 Ca3 Co4 O9 fiber texture of the film with the (001) pole parallel to the surface normal. Single-crystal-like second phases, CaCo Si2 O6 and CoO, presumably the interface reaction products of Ca3 Co4 O9 with the substrate Si, were identified. The near four-fold symmetry and the similar intensity displayed by the 220 reflection from the CaCo Si2 O6 structure indicated an epitaxial relation between CaCo Si2 O6 and Si, with four symmetry-induced variants being generated with approximately equal volume fractions.