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

Abstract

Cu(2+)-doped Pb[Zr(0.54)Ti(0.46)]O(3) (PZT) and Cu(2+)-doped [K(0.5)Na(0.5)]NbO(3) (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 Cu(2+) 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 Cu(2+)-defect center for morphotropic phase boundary compositions between the two systems. In particular, it is found that Cu(2+)-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.

Antiferroelectric-like properties and enhanced polarization of Cu-doped K0.5Na0.5NbO3 piezoelectric ceramics

“…It is clearly seen that DC1 contains an electric dipole moment (P D ), while the dipole moment for trimeric DC2 almost vanishes due to its symmetric configuration. 14 Because of its non-dipolar nature, DC2 cannot provide enough driving force for domain back-switching and thus did not induce the double P-E loops in KNN15. A slightly constricted P-E loop might be expected for KNN15 at room temperature considering the existence of a small portion of DC1.…”

“…13) and is subsequently confirmed by the EPR spectrum. 14,15 Non-switchable DCs that are aligned opposite to the spontaneous polarization (P s ) direction provide the driving force for domain backswitching after the removal of the external electric field, similar to the antiferroelectric behavior. For KNN10, the DCs would be quite mobile at temperatures above 130 C, and hence the external dc field resulted in a redistribution of the defects and the consequential development of E ib .…”

Effect of donor and acceptor dopants on fatigue properties in PZT thin films

“…Nevertheless, the reduction of switchable polarization appeared earlier than that in PZT films. A possible mechanism for this phenomenon is that Cu 2 þ occupied the B-site (Ti 4 þ and Zr 4 þ ) in PZT [9] and the charge difference was compensated by oxygen vacancies as shown in Eq. (3).…”

Effect of high density and reduced ionic defects on piezoelectric behavior of K0.5Na0.5NbO3 ceramic

“…However, since the melting points of two carbonates lie in the temperature range of 800-900°C, loss of alkali ions cannot be ruled out during calcination in this temperature range, prior to the chemical reaction among the precursors. This loss is expected to lead to the deficiency of A-site cations in KNN lattice and hence creation of defect complexes and high conductivity [25,26].…”