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ICMCTF - 2014
Christian Koller (C.M. Koller)
"Impact of point defects on stability of (Al1-xCrx)2O3 phases from first principles"
C. M. Koller1, J. Ramm2, P. Polcik3, D. Holec4, J. Paulitsch5, P. H. Mayrhofer1,5
1 Christian Doppler Laboratory of Application Oriented Coating Development, Vienna University of Technology, Vienna, A-1040, Austria
2 Oerlikon Balzers Coating AG, Balzers, LI-9496, Principality of Liechtenstein
3 Plansee Composite Materials GmbH, Lechbruck am See, D-86983, Germany
4 Department of Physical Metallurgy and Materials Testing, Montanuniversität Leoben, Leoben, A-8700, Austria
5 Institute of Materials Science and Technology, Vienna University of Technology, Vienna, A-1040, Austria
A central subject of current protective coating development is the phase formation in low temperature physical vapour deposited, PVD, (Al1-xCrx)2O3 coatings. Experimental results have shown that magnetron sputtered or arc evaporated coatings synthesised at temperatures as low as 500 °C usually crystallise in an amorphous or metastable face centred cubic based phases, like the defect-spinel ?- or the B1-type. This is however in contradiction to ab initio phase stability predictions, which suggest the desired and industrially important corundum type solid solution ?-(Al1-xCrx)2O3 to have lower energy of formation, thus being the stable phase and preferentially formed.
Within our investigations of three phases (corundum ?, defect-spinel ?, and B1-like fcc) across all Al compositions, x, of (Al1-xCrx)2O3 we find that the ? solid solution is more sensitive to randomly generated defects than the ?-type and B1-type. We propose that these findings in addition to exceptionally high surface energies for certain terminations of the corundum structure can explain the favoured formation of ?- and B1-(Al1-xCrx)2O3 during low temperature PVD processes, which generally lead to high defect densities and small crystallite sizes.

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