Přednášející: Nava Setter (EPFL Swiss Federal Institute of Technology, Lausanne, Switzerland)
Místo: Seminární místnost 117, FZU Na Slovance
Jazyk: anglicky
Pořadatelé:
Oddělení dielektrik
The cubic (or pseudo-cubic) crystalline structure of perovskite ferroelectrics does not lend itself easily to one-dimensional growth. For this reason only rare reports exist on growth and properties of these materials. On the other hand, those rare reports intrigued us to pursue growth in order to study the properties of these nanowires with particular attention to size dependent properties and their potential implication.
Reduction in dimensions of ferroelectrics, e.g. ultra-thin layers, results typically in deterioration of properties or at best maintenance of the bulk properties of the material. Is this a general phenomenon? We explored this question in the case of PZT nano-wires.
The main emphasis was on the growth of perovskite nano-wires. Two materials, KNbO3 and PZT were successfully grown. The growth mechanism(s) were explored and the role of templates understood. The structure of the wires is presented, including the orientation of the spontaneous polarisation relative to the crystallographic orientation of the geometrical axes of the wires. The piezoelectric properties were investigated. The situation in which the polarization axis is inclined to the axis of the wire in a mono-domain nanowire was analysed theoretically. Such a situation corresponds, for example, to a practical case where the nanowire axis of a tetragonal PZT is not [001]. In this configuration, the depolarization field, opposing the spontaneous polarization leads to polarization rotation. In particular diameters and orientations, the appearance of new phases is predicted. Size effect on properties, such as enhancement of Tc is discussed with both positive and negative effect possible. A case where Tc is enhanced is demonstrated experimentally.
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