[1] Univ Bayreuth, CME, D-95440 Bayreuth, Germany
[2] Univ Limoges, CNRS, IRCER, UMR 7315, F-87000 Limoges, France
[3] UM, IEM, UMR 5635, CNRS,ENSCM, Pl E Bataillon, F-34095 Montpellier, France
[4] HC Starck Tantalum & Niobium GmbH, Schleeke 78-91, D-38642 Goslar, Germany
[5] Tech Univ Darmstadt, Inst Mat Wissensch, Otto Berndt Str 3 Room 407, D-64287 Darmstadt, Germany