Peter Neumeister

Polarization characterization of PZT disks and of embedded PZT plates by thermal wave methods

In this work, the thermal wave method was applied to characterize PZT disks and embedded PZT plates with regard to the polarization magnitude and spatial homogeneity. The samples were exposed to periodic heating by means of a laser beam and the pyroelectric response was determined. Thermal relaxation times (single time constants or distributions of time constants) describe the heat losses of the PZT samples to the environment. The resulting pyroelectric current spectrum was fitted to the superposition of thermal relaxation processes. The pyroelectric coefficient gives insight in the polarization distribution. For PZT disks, the polarization distribution in the surface region showed a characteristic decrease towards the electrodes.

Continuum analysis of the nucleus growth of reverse domains in large ferroelectric crystals

Polarization reversal in ferroelectrics arises due to domain nucleation and domain wall motion. The nucleation of reverse domains at crystal boundaries is the fundamental initiation process observed in single crystals. The classical continuum approach by Landauer determines an insurmountable energy barrier to extrinsic domain nucleation. We rediscuss the continuum approach. Predetermined surface states are found to be a misleading concept. Alternate energy contributions, for example, due to a dead layer or due to charge injection as well as reduced domain wall energy and anisotropy of domain wall energy, have to be included into a convincing picture of domain nucleation.

0.92 Pb(Mg 1/3 Nb 2/3 )O 3 — 0.08 PbTiO 3 relaxor ferroelectrics modified with different dopants for electrocaloric cooling application

In the present work we investigate the influence of acceptor (K⁺, Cu⁺, Li⁺), donor (La³⁺, Bi³⁺, Eu³⁺, Nd³⁺, Y³⁺, Cr³⁺) and charge equivalent dopants (Sr²⁺, Co²⁺, Mn²⁺, Ta⁵⁺) on the dielectric and ferroelectric behavior of 0.92 Pb(Mg<inf>1/3</inf>Nb<inf>2/3</inf>)O<inf>3</inf>-0.08 PbTiO<inf>3</inf>(0.92PMN-0.08PT). As a criterion for the basic suitability for electrocaloric cooling application, we directly measure the temperature change (ΔT) upon the application and withdrawal of an electric field as a function of the ambient temperature. For the undoped 0.92PMN-0.08PT bulk ceramics fabricated by the columbite route, we observed the maximum ΔT of 0.24 K when applying an electric field of 2 kv-rnm⁻¹ at 28°C (ΔT<inf>up</inf>). Withdrawing the electric field at same conditions showed a temperature decrease of 0.20 K (ΔT<inf>down</inf>). The resulting ΔT<inf>down</inf>:ΔT<inf>up</inf> ratio is also considered.