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Title: First principles studies on the impact of point defects on the phase stability of (Al{sub x}Cr{sub 1−x}){sub 2}O{sub 3} solid solutions

Density Functional Theory applying the generalised gradient approximation is used to study the phase stability of (Al{sub x}Cr{sub 1−x}){sub 2}O{sub 3} solid solutions in the context of physical vapour deposition (PVD). Our results show that the energy of formation for the hexagonal α phase is lower than for the metastable cubic γ and B1-like phases–independent of the Al content x. Even though this suggests higher stability of the α phase, its synthesis by physical vapour deposition is difficult for temperatures below 800 °C. Aluminium oxide and Al-rich oxides typically exhibit a multi-phased, cubic-dominated structure. Using a model system of (Al{sub 0.69}Cr{sub 0.31}){sub 2}O{sub 3} which experimentally yields larger fractions of the desired hexagonal α phase, we show that point defects strongly influence the energetic relationships. Since defects and in particular point defects, are unavoidably present in PVD coatings, they are important factors and can strongly influence the stability regions. We explicitly show that defects with low formation energies (e.g. metal Frenkel pairs) are strongly preferred in the cubic phases, hence a reasonable factor contributing to the observed thermodynamically anomalous phase composition.
Authors:
 [1] ;  [2] ;  [3] ;  [4] ; ;  [1] ;  [5] ;  [1] ;  [5]
  1. Christian Doppler Laboratory for Application Oriented Coating Development, TU Wien, Vienna, 1060 (Austria)
  2. Faculty of Science, Masaryk University, Kotlářská 2, Brno, 61137 (Czech Republic)
  3. Oerlikon Balzers, Oerlikon Surface Solutions AG, Balzers, 9496 (Liechtenstein)
  4. Plansee Composite Materials GmbH, Lechbruck am See, 86983 (Germany)
  5. (Austria)
Publication Date:
OSTI Identifier:
22492425
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Advances; Journal Volume: 6; Journal Issue: 2; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ALUMINIUM OXIDES; CHROMIUM OXIDES; COATINGS; DENSITY FUNCTIONAL METHOD; FORMATION HEAT; FRENKEL DEFECTS; PHASE STABILITY; PHYSICAL VAPOR DEPOSITION; SOLID SOLUTIONS; SYNTHESIS