1. a Institute of Physics of Materials, Academy of Sciences of the Czech Republic , Žižkova 22, CZ-616 62 Brno, Czech Republic
2. b Institute of Mechanics, Montanuniversität Leoben , Franz-Josef-Straße 18, A-8700 Leoben, Austria
3. c Erich Schmid Institute of Materials Science, Austrian Academy of Sciences , Jahnstraße 12, A-8700 Leoben, Austria