Field of Expertise: Advanced Material Science

The antiferroelectric Lanthanum-modified Lead Zirconate Titanate: A material for power devices
Theresa Kainz
15:20 - 17:30 Thursday 24 October 2013 Foyer Alte Technik

Antiferroelectric ceramics have gained considerable interest as materials for charge storage devices and are key components for hybrid transmission technologies. This resulted in a revival of Lanthanum-modified Lead Zirconate Titanate. The solid solution of Lead-Zirconate and Lead-Titanate, abbreviated as PZT, appears in the perovskite structure ABO3 with various symmetries depending on the Zr/Ti ratio. The A-site is occupied by the lead ion and the B-site by zirconium and titanum ions. The orthorhombic zirconium rich compound represents the antiferroelectric phase, increasing Ti-content causes the formation of ferroelectric phases. The ferroelectric behaviour is associated with a large spontaneous electric polarization at zero field due to the displacement of the B-cations. In the antiferroelectric phase, the neighbouring dipoles originating from the displacement of Lead ions are antiparallel, therefore no spontaneous macroscopic polarization is observed. If the material is subjected to electric field, the antiparallel dipoles can be switched and forced to be parallel. This leads to an electric field-induced phase transition from the antiferroelectric to the ferroelectric phase. As a result a double-hysteresis loop appears as a function of the applied field on the polarization and the antiferroelectric phase is capable of storing and releasing electric energy. Additionally, the phase transition is accompanied by a change in linear dimensions and optical properties. Therefore the technical applications entail digital displacement transducers, energy storage capacitors, electrocaloric cooling devices and many more. By substituting Lead by the aliovalent Lanthanum the stability range of the antiferroelectric phase near the Zirconium rich side is increased. But the dominant phase is highly sensitive to subtle changes in stoichiometric composition and processing. In this contribution, a short presentation of the properties and applications is given. The processing options and the influencing parameters are demonstrated and experimental results of the modification of the polarization behaviour are illustrated.