Erdem, Emre ; Eichel, Rüdiger-A.
Lallart, Mickael (ed.) (2011):
Impact of Defect Structure on ’Bulk’ and Nano-Scale Ferroelectrics.
In: smart materials, In: Ferroelectrics - Characterization and Modeling, pp. 79-96, open access book, Intech open access publischer, ISBN 978-953-307-455-9,
[Book Section]

Abstract

Ferroelectric materials offer a wide range of dedicated physical properties such as high dielectric constant, spontaneous polarisation, pyroelectric and piezoelectric effects which can be applied in thin-film non-volatile memories or ‘bulk’ actuators, multi-layer capacitors, thermal sensors and transducers (1–3). In that respect, desiredmaterials properties for specific applicationsmay be tailored by controlling the defect structure bymeans of aliovalent doping, rendering so-termed ’hard’ or ’soft’ piezoelectric materials (4–6). Another important impact on ferroelectric properties results from the confined size in nano-scale architectures (7). At the nanometer scale physical and chemical properties are expected to differ markedly from those of the ’bulk’ material. Owing to a size-driven phase transition, a critical particle size exists below which ferroelectricity does no longer occur (8). In this chapter, we will first outline the nature of the size-driven para-to-ferroelectric phase transition, as well as the concepts of defect chemistry. On that basis, the interplay between confined size at the nano-regime and the development of defect structure will be characterized. The here studied ferroelectric lead titanate nano-powders may be considered as a model system for more complex ferroelectric nano architectures (1; 2). Furthermore, the results discussed here may be transferred to large extent to other important perovskite oxides with divalent A- and tetravalent B-site, such as BaTiO3 or Pb[Zr,Ti]O3 (PZT). The defect chemistry of ferroelectric perovskite oxideswith monovalent A- and pentavalent B-site, such as the [K,Na]NbO3 (KNN) solid solution system, however has shown some important deviations from the defect structure characterized for PZT compounds (9; 10).

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