Iron-oxygen vacancy defect association in polycrystalline iron-modified PbZrO3 antiferroelectrics: Multifrequency electron paramagnetic resonance and Newman superposition model analysis

By utilizing multifrequency electron paramagnetic resonance (EPR)
spectroscopy, the iron functional center in Fe3+-modified
polycrystalline lead zirconate (PbZrO3) was studied. The single phase
polycrystalline sample remained orthorhombic and antiferroelectric down
to 20 K as confirmed by high-resolution synchrotron powder diffraction.
The Fe3+ ions were identified as substituting for Zr4+ at the B-site of
the perovskite ABO(3) lattice. Similarly as found for Fe3+:PbTiO3
[Mestric , Phys. Rev. B 71, 134109 (2005)], the value of the
fine-structure (FS) parameter B-2(0) is only consistent with a model in
which a charged (Fe-Zr(')-V-O(center dot center dot))(center dot)
defect associate is formed. In contrast to a well defined iron
functional center in lead titanate (PbTiO3) with FS parameters
exhibiting variances of less than 3%, a strong broadening of the EPR
powder pattern was observed in lead zirconate, indicating a much larger
variance of FS parameters. It is suggested that the apparent broad
distribution of fine-structure parameters arises from the system's
capability to realize different oxygen vacancy positions in the first
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coordination shell around the iron site. This proposed model of a small
number of distinct iron-oxygen vacancy sites is supported by the
observation that corresponding B-2(0) and orthorhombic B-2(2) FS
parameters of these sites are anticorrelated, a property not expected
for random distributions of fine-structure parameters.