Size effects in chromium-doped PbTiO3 nanopowders observed by multi-frequency EPR

Abstract

A multi-frequency (X, Q, and W band) electron paramagnetic resonance (EPR) study of Cr-doped PbTiO3 micro- and nanopowder samples was performed. Three Cr3+ 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 PbTiO3 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 deltaD, was assumed. The variation of D and deltaD 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 Cr3+ 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.

Speciation of Cr(iii) in intermediate phases during the sol–gel processing of Cr-doped SrTiO3powders

“…Additional weaker peaks surrounding the intense central EPR signal in all the spectra shown in Fig. 4 originate from the nuclear-electron hyperne interaction of 53 Cr and from small axial zero-eld splittings of the 4 A 2 ground term of Cr 3+ . Fig.…”

“…The electron-nuclear hyperne coupling from 53 Cr nuclear spins (I ¼ 3/2, 9.5% relative abundance) is parameterized by A; the Landé factor is given by the g tensor, which is slightly anisotropic (g z s g x,y ) in an axial crystal eld (D s 0), b is the bohr magneton; and B is the external magnetic eld.…”

Defect structure and formation of defect complexes in Cu2+-modified metal oxides derived from a spin-Hamiltonian parameter analysis

“…In particular, recent methododical advances concerning the use of high frequencies [18][19][20][21] and pulsed microwave fields [4,22,23] have allowed for an accurate determination of spinHamiltonian parameters. However, as compared to the high-spin ions Fe 3+ and Mn 2+ , both of which have a 3d…”

A novel method for the preparation of solvent-free, microwave-assisted and nitrogen-doped carbon dots as fluorescent probes for chromium(vi) detection and bioimaging

“…1,2 Chromium (Cr) is one of the most toxic heavy metal ions, and its common valence states are Cr(III) and Cr(VI). Cr(III) has been broadly employed as a dopant in lead titanate nanopowders for multi-frequency electron paramagnetic resonance studies, [3][4][5] whereas Cr(VI) is more toxic as compared to Cr(III) due to its higher solubility in water. Due to its solubility, Cr(VI) readily enters into the bodies of living organisms and induces mutagenic and carcinogenic risks.…”