title: Complementary ab initio and X-ray nanodiffraction studies of Ta2O5.
abstract: The complex structure of Ta2O5led to the development of various structural models. Among them, superstructures represent the most stable configurations. However, their formation requires kinetic activity and long-range ordering processes, which are hardly present during physical vapor deposition. Based on nano-beam X-ray diffraction and concomitant ab initio studies, a new metastable orthorhombic basic structure is introduced for Ta2O5with lattice parametersa= 6.425 Å,b= 3.769 Å andc= 7.706 Å. The unit cell containing only 14 atoms, i.e. two formula unit blocks in thecdirection, is characterized by periodically alternating the occupied oxygen site between two possible positions in succeeding 002-planes. This structure can be described by the space group 53 (Pncm) with four Wyckoff positions, and exhibits an energy of formation of -3.209 eV atom-1. Among all the reported basic structures, its energy of formation is closest to those of superstructures. Furthermore, this model exhibits a 2.5 eV band gap, which is closer to experimental data than the band gap of any other basic-structure model. The sputtered Ta2O5films develop only a superstructure if annealed at temperatures >800 °C in air or vacuum. Based on these results and the conveniently small unit cell size, it is proposed that the basic-structure model described here is an ideal candidate for both structure and electronic state descriptions of orthorhombic Ta2O5materials.
authors: Christian Doppler Laboratory for Application Oriented Coating Development at the Institute of Materials Science and Technology, Vienna University of Technology, A-1040 Vienna, Austria.
authors: R
authors: R
authors: Hollerweger
authors: Department of Physical Metallurgy and Materials Testing, Montanuniversität Leoben, A-8700 Leoben, Austria.
authors: D
authors: D
authors: Holec
authors: Institute of Materials Science and Technology, Vienna University of Technology, A-1040 Vienna, Austria.
authors: J
authors: J
authors: Paulitsch
authors: Christian Doppler Laboratory for Application Oriented Coating Development at the Institute of Materials Science and Technology, Vienna University of Technology, A-1040 Vienna, Austria.
authors: M
authors: M
authors: Bartosik
authors: Department of Physical Metallurgy and Materials Testing, Montanuniversität Leoben, A-8700 Leoben, Austria.
authors: R
authors: R
authors: Daniel
authors: Oerlikon Balzers Coating AG, LI-9496 Balzers, Liechtenstein.
authors: R
authors: R
authors: Rachbauer
authors: Plansee Composite Materials GmbH, D-86983 Lechbruck am See, Germany.
authors: P
authors: P
authors: Polcik
authors: Department Materials Physics, Montanuniversität Leoben and Materials Center Leoben, A-8700 Leoben, Austria.
authors: J
authors: J
authors: Keckes
authors: Ruprecht Haensel Laboratory, University of Kiel, Leibnizstrasse 19, D-24098 Kiel and Helmholtz-Zentrum Geesthacht, Institute for Materials Research, D-21502 Geesthacht, Germany.
authors: C
authors: C
authors: Krywka
authors: Institute of Materials Science and Technology, Vienna University of Technology, A-1040 Vienna, Austria.
authors: H
authors: H
authors: Euchner
authors: Christian Doppler Laboratory for Application Oriented Coating Development at the Institute of Materials Science and Technology, Vienna University of Technology, A-1040 Vienna, Austria ; Institute of Materials Science and Technology, Vienna University of Technology, A-1040 Vienna, Austria.
authors: P H
authors: PH
authors: Mayrhofer
keywords: Ab initio; DOS; Nanobeam diffraction; Structure; Ta2O5
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