The defect structure of Fe3+-, Cu2+-, Mn4+- and Gd3+-doped PbTiO3 nano-powders was studied by electron paramagnetic resonance spectroscopy. Analogous to the situation for 'bulk' ferroelectrics, Fe3+ and Cu2+ acted as acceptor-type functional centers that form defect complexes with charge-compensating oxygen vacancies. The corresponding defect dipoles were 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 was modified such that orientations perpendicular to PS, (FeTi’–VO••)┴• and (CuTi’’-VO••)┴x also became realized. Moreover, the binding energy for the defect complexes was lowered such that instead 'free' FeTi' and VO••-centers were formed. As a consequence, the concentration of mobile VO•• that enhances the ionic conductivity through drift diffusion was increased for the nano-powders. Finally, in the nano-regime the ferroelectric 'hardening' was expected to be considerably decreased as compared to the 'bulk' compounds. In contrast to the acceptor-type dopants, the donor-type Gd3 + dopant was incorporated as an 'isolated' functional center, where charge compensation by means of lead vacancies was performed in distant coordination spheres.

Defect Structure in Aliovalently-Doped and Isovalently-Substituted PbTiO3 Nano-Powders. E.Erdem, P.Jakes, S.K.S.Parashar, K.Kiraz, M.Somer, A.Rüdiger, R.A.Eichel: Journal of Physics - Condensed Matter, 2010, 22[34], 345901