title: Defect structure in aliovalently-doped and isovalently-substituted PbTiO3 nano-powders.
abstract: The defect structure of Fe(3+)-, Cu(2+)-, Mn(4+)- and Gd(3+)-doped PbTiO(3) nano-powders has been studied by electron paramagnetic resonance (EPR) spectroscopy. Analogous to the situation for 'bulk' ferroelectrics, Fe(3+) and Cu(2+) 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, P(S), and possess an additional defect polarization, P(D). Upon the transition to the nano-regime, the defect structure is modified such that orientations perpendicular to P(S), [Formula: see text] and [Formula: see text] also become realized. Moreover, the binding energy for the defect complexes is lowered such that instead 'free' Fe'(Ti) and V··(O)-centers are formed. As a consequence, the concentration of mobile V··(O) 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 Gd(3+) dopant is incorporated as an 'isolated' functional center, where charge compensation by means of lead vacancies is performed in distant coordination spheres.
authors.affiliation: Institut für Physikalische Chemie I, Universität Freiburg, Freiburg, Germany.
authors.forename: Emre
authors.initials: E
authors.lastname: Erdem
authors.forename: Peter
authors.initials: P
authors.lastname: Jakes
authors.forename: S K S
authors.initials: SK
authors.lastname: Parashar
authors.forename: Kamil
authors.initials: K
authors.lastname: Kiraz
authors.forename: Mehmet
authors.initials: M
authors.lastname: Somer
authors.forename: Andreas
authors.initials: A
authors.lastname: Rüdiger
authors.forename: Rüdiger-A
authors.initials: RA
authors.lastname: Eichel