Local variations in defect polarization and covalent bonding in ferroelectric Cu2+-doped PZT and KNN functional ceramics at the morphotropic phase boundary

Abstract

Cu²⁺-doped Pb[Zr_0.54Ti_0.46]O₃ (PZT) and Cu²⁺-doped [K_0.5Na_0.5]NbO₃ (KNN) ferroelectrics with a dopant concentration of 0.25 mol% were investigated by means of multi-frequency and multi-pulse electron paramagnetic resonance (EPR) spectroscopy. Through the use of high magnetic fields and pulsed microwave fields an enhanced resolution was achieved yielding valuable information about the structural distortion at the dopant site. The results obtained suggest that Cu²⁺ substitutes for both systems as an acceptor centre for the perovskite B-site. For reasons of local charge compensation, different kinds of defect associates invoking one and two oxygen vacancies are formed. These two kinds of extended defects differ in their electric and elastic properties. The results obtained are analyzed in order to characterize differences of the local structure in the Cu²⁺-defect center for morphotropic phase boundary compositions between the two systems. In particular, it is found that Cu²⁺-doping in KNN creates 50% more oxygen vacancies than the same amount of copper in PZT. Furthermore, local differences in covalent and ionic bonding are monitored.