Parts | Days | Selection | Search | Updates | Downloads | Help

MM: Fachverband Metall- und Materialphysik

MM 38: Topical Session Diffussionless Transformations I

MM 38.6: Topical Talk

Thursday, March 17, 2011, 15:30–16:00, IFW D

Phase Transformations in Bi-based lead-free piezoceramics — •Jürgen Rödel and Wook Jo — Institute of Materials Science, Technische Universität Darmstadt,, Darmstadt, Germany

Piezoceramics in the application as an actuator experience electric fields between 0 and 3 kV/mm and temperatures between -30°C and 150°C with uniaxial stress up to 40 MPa. Lead-containing materials have relied on the concept of a morphotropic phase boundary (MPB), where similar free energy functions between rhombohedral and tetragonal afford easy polarization rotation and domain switching.

In this talk, the focus will be placed on the main lead-free piezoceramic material with MPB. Bismuth-Natrium-Niobate (BNT) - Barium titanate (BT)exhibits a pseudocubic structure at the MPB, which transforms irreversibly into a mixture of tetragonal and rhombohedral phases upon poling. this transformation, however, is reversible, if small amounts of Niobates are added. This leads to a very field-induced strain (poling strain+unipolar strain). the phase transition behavior will be presented utilizing in-situ (under electric field) investigations under synchrotron diffraction, neutron diffraction and in the TEM. Further, first diffuse scattering measurements on single crystals will be presented. Some of these measurements have been performed as function of temperature and are always discussed with respect to salient electrical performance.