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Size effects in chromium‐doped PbTiO 3 nanopowders observed by multi‐frequency EPR
Author(s) -
Erdem Emre,
Böttcher Rolf,
Gläsel HansJürgen,
Hartmann Eberhard
Publication year - 2005
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1664
Subject(s) - chemistry , chromium , electron paramagnetic resonance , doping , chemical engineering , nuclear magnetic resonance , nuclear chemistry , condensed matter physics , organic chemistry , physics , engineering
Abstract A multi‐frequency (X, Q, and W band) electron paramagnetic resonance (EPR) study of Cr‐doped PbTiO 3 micro‐ and nanopowder samples was performed. Three Cr 3+ centres were identified in tetragonal phase samples with different axial Zero Field Splitting (ZFS) parameters, C1, C2, and C3. The centre C1 is similar to that observed in previous X‐band crystal and ceramic sample measurements. The superposition model by Newman and Urban was applied to translate the ZFS data into local displacements inside the distorted oxygen octahedra of the PbTiO 3 lattice. In the tetragonal phase, only the centre C1 was observed. The powder spectra were fitted using a spin‐Hamiltonian in which a Gaussian distribution of ZFS terms, characterized by a mean value D and distribution width Δ D , was assumed. The variation of D and Δ D with mean particle size was determined. A critical particle size, d cr , exists, particles smaller than this size remain in the cubic phase for all temperatures, there is a size‐driven tetragonal‐to‐cubic phase transition. Particles with d < d cr were found to give a new Cr 3+ centre spectrum, C4, consisting of a single line with an isotropic g‐factor, so allowing the cubic phase content to be quantified. Further, temperature‐dependent EPR measurements were made, which allowed the variation in Curie temperature with mean particle size to be determined. Copyright © 2005 John Wiley & Sons, Ltd.