Erdem, Emre ; Jakes, Peter ; Parashar, S. K. S. ; Kiraz, Kamil ; Somer, Mehmet ; Rüdiger, Andreas ; Eichel, Rüdiger-A. (2010):
Defect structure in aliovalently-doped and isovalently-substituted PbTiO3nano-powders.
In: Journal of Physics: Condensed Matter, 22 (34), pp. 345901-1. ISSN 0953-8984,
[Article]

Abstract

The defect structure of Fe3 + -, Cu2 + -, Mn4 + - and Gd3 + -doped PbTiO3 nano-powders has been studied by electron paramagnetic resonance (EPR) spectroscopy. Analogous to the situation for 'bulk' ferroelectrics, Fe3 + and Cu2 + act as acceptor-type functional centers that form defect complexes with charge-compensating oxygen vacancies. The corresponding defect dipoles are aligned along the direction of spontaneous polarization, PS, and possess an additional defect polarization, PD. Upon the transition to the nano-regime, the defect structure is modified such that orientations perpendicular to PS, (FeTi'–V0°°)°_ and (Cu''Ti-V0°°)_* also become realized. Moreover, the binding energy for the defect complexes is lowered such that instead 'free' FeTi' and V0°°-centers are formed. As a consequence, the concentration of mobile V0°° that enhances the ionic conductivity through drift diffusion is increased for the nano-powders. Finally, in the nano-regime the ferroelectric 'hardening' is expected to be considerably decreased as compared to the 'bulk' compounds. In contrast to the acceptor-type dopants, the donor-type Gd3 + dopant is incorporated as an 'isolated' functional center, where charge compensation by means of lead vacancies is performed in distant coordination spheres.

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