The CPP (combined polymerization and pyrolysis) preparation route, in its enhanced
liquid-precursor-based version, was combined with consecutive soft milling. For studies of
temperature- and size-dependent structural changes occurring in ferroelectric lead titanate,
this combined route yields a nanopowder series covering the relevant particle-size region at
target quality. This material basis enables consistent SEM, TEM, XRD, Raman,
EPR and dielectric measurements, which furnish a comprehensive picture of the
cooperation between temperature rise and size reduction to eliminate tetragonality and
concomitant ferroelectricity. Our previous original EPR studies on nanosized barium
titanate are now extended to the lead titanate case. Furthermore, as compared
to the pertinent literature standard, the materials basis is extended to powder
samples of smaller mean particle sizes, comprising the critical size at which a
PbTiO3
particle undergoes a transition into cubic paraelectric phase. Thus, the size-driven phase
transition can be observed in a direct way (at 7 nm, which compares to 40 nm for
BaTiO3),
and the EPR data suggest a much less spacious gradient shell at the particle surfaces (thickness
≈
2 nm) than in previous analogous investigations on
BaTiO3
(15 nm).
The coordination geometry of the tetrapyridine−copper(II)
complex in frozen solution is investigated by
proton and deuterium two-dimensional hyperfine sublevel correlation
spectroscopy (HYSCORE) electron
spin resonance experiments. In particular, the deuterium
experiment demonstrates the potential of this method,
which lies in the superior spectral resolution of the two-dimensional
spectra. This allows us to resolve deuterium
nuclear quadrupole splittings of the cross peak ridges even in
orientationally disordered systems, which in
turn yield structural information about the overall complex symmetry.
Proton and deuterium experiments
show pronounced cross peak ridges from protons and deuteriums at the C2
and C6 carbon atoms of the
pyridine molecule. The coordination geometry within the complexes
could be deduced from orientation-selective deuterium spectra. Severe deviations from the
D
4
h
complex symmetry were
found in such a way
that the pyridine molecules are arranged with their molecular mirror
plane perpendicular to the complex
plane. The complex geometry experiences a significant variance
with respect to the Cu−N bond directions
due to random spatial constraints induced by solvent
molecules.
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