Math-Sci Seminar

Speaker: Dr. Emre Erdem, Darmstadt University of Technology, Germany

Title:  Modern Electron Paramagnetic Resonance Spectroscopy - EPR in Nano Science
Size effects in Chromium doped PbTiO3 nanopowders
        (ATTENTION TO UNUSUAL TIME, DAY AND PLACE)

Date: Fri 13 Nov, 2006
Time: 14:00
Place: Science Building, Room Z24


Abstract:
Lead titanate (PbTiO3) nanopowders were prepared from a monomeric
metallo-organic precursor through combined solid-state
polymerisation and pyrolysis (CPP). This makes it possible to adjust
the mean particle size in a wide range by just choosing the
appropriate reaction temperature. Moreover, the potential of the CPP
route is enhanced to prepare perovskitic stoichiometric solutions
for advanced practical applications. The size effects in the
resulting PbTiO3 nanopowders were investigated by standard methods
such as X-ray diffraction (XRD), transmission electron microscopy
(TEM), FT-Raman spectroscopy and dielectric spectroscopy. By
reducing the size Curie temperature and tetragonality decreases
drastically and finally below 6 nm ferroelectricity disappears. In
multi-frequency EPR study of Cr doped PbTiO3 nanopowder samples with
varying mean particle size, three paramagnetic Cr3+ centres (C1, C2,
C3) with different axial fine structure (FS) parameters are
identified. When going to samples with mean particle size at
nanoscale, other than the centre C1 are no longer detectable.
Instead, a new one (C4) appears, testifying a pronounced size
effect.

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