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An experimental and theoretical study on the crystal structure and elastic properties of Ta 1-xOx coatings

: Almeida Alves, C.F.; Marques, Luís Silvino Alves; Calderon, S.V.; Ferreira, Paulo J.; Schneider, Dieter; Cavaleiro, Albano J.; Carvalho, S.


Surface and coatings technology 364 (2019), S.289-297
ISSN: 0257-8972
Fraunhofer IWS ()
Tantalum oxide coatings; magnetron sputtering; ab-initio; STEM; elastic modulus

The production of Ta1-xOx coatings has attracted a lot of attention due to their wide variety of industrial applications. Nonetheless, to properly control the functional properties of these coatings, a good understanding of their structural properties must be achieved. Ta1-xOx phases have structural similarities since they are formed by the distortion of the body centered cubic (bcc) Ta structure and, therefore, a clear and unequivocal identification of the crystalline phases is not trivial. In this regard, this work proposes a theoretical and experimental study to understand the evolution of the structural and the elastic properties of Ta-based coatings. The coatings were deposited by magnetron sputtering as a function of oxygen content and characterized by EPMA (electron probe microanalysis), XRD (X-ray diffraction), STEM (scanning transmission electron microscopy) and SAW (surface acoustic waves). The results demonstrate the formation of a bcc α-Ta phase in the non-reactive Ta coating, which transitions to a mixture of crystalline tantalum and tantalum oxide phases for low oxygen concentrations while amorphous phases are observed for high oxygen levels. Ab-initio calculations of different Ta-O phases are in good agreement with the experimental results and reveal that the oxygen addition to the metallic Ta phase, leads to a distortion of the Ta crystal structure, causing a decrease in density and an increase of the elastic constants.