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DF: Fachverband Dielektrische Festkörper
DF 10: Dielectric and Ferroelectric Thin Films and Nanostructures III
DF 10.2: Vortrag
Donnerstag, 29. März 2007, 14:50–15:10, H48
Characterisation of Ferroelectric Nanoparticles by HRTEM and Electron Holography — •Margarita Weiß1,4, Hannes Lichte1, Gil Markovich2, Tcipi Fried2, Sebastian Wohlrab3, and Michael Lehmann4 — 1Institut für Strukturphysik, TU Dresden, 01062 Dresden — 2School of Chemistry, Tel Aviv University, Tel Aviv 69978, Israel — 3Institut für Anorganische Chemie, TU Dresden, 01069 Dresden — 4Institut für Optik und Atomare Physik, TU Berlin, 10623 Berlin
As bulk materials, BaTiO3 and PbTiO3 are known to be ferroelectric below their Curie temperature of Tc=120°C and Tc=480°C, respectively. However, ferroelectric nanoparticles show different properties. For example, there is a critical size effect, in that the Curie temperature Tc is decreasing with decreasing particle size. Unfortunately, there are no reliable figures in literature for the critical size, below which ferroelectricity is not observed.
In this work, particles of the size of 10nm up to around 100 nm were investigated by means of electron holography, which allows directly measuring the atomic ferroelectric polarisation as well as electric stray fields around nano-sized specimens. There are no indications for electric dipole stray fields around the ferroelectric particles. But BaTiO3 particles of a diameter of about 40 nm show hints for interior ferroelectric polarisation, whereas smaller particles do not reveal any indication of ferroelectricity. By HRTEM investigations it was observed that lattice planes of these small particles are very inhomogeneous. This might prevent the ferroelectric polarisation.