1. Division Advanced Technical Ceramics, Bundesanstalt fuer Materialforschung und -pruefung BAM, 12200 Berlin, Germany
2. Faculty of Engineering Science, University of Bayreuth, 95440 Bayreuth, Germany
3. Laboratoire GREMAN CNRS-UMR 7347, IUT de BLOIS, 41029 Blois Cedex, France