Cr³⁺ Electron Paramagnetic Resonance Study of Sn_1−xCr_xO2(0.00 ≤ x ≤ 0.10)

This paper reports on the liquid-helium-temperature (5 K) electron paramagnetic resonance (EPR) spectra of Cr ³⁺ ions in the nanoparticles of SnO ₂ synthesized at 600 °C with concentrations of 0%, 0.1%, 0.5%, 1%, 1.5%, 2.0%, 2.5%, 3.0%, 5.0%, and 10%. Each spectrum may be simulated as overlap of spectra due to four magnetically inequivalent Cr ³⁺ centers characterized by different values of the spin-Hamiltonian parameters. Three of these centers belong to Cr ³⁺ ions in orthorhombic sites, situated near oxygen vacancies, characterized by very large zero-field splitting parameters D and E , presumably due to the presence of nanoparticles in the samples. The fourth EPR spectrum belongs to the Cr ³⁺ ions situated at sites with tetragonal symmetry, substituting for the Sn ⁴⁺ ion, characterized by a very small value of D . In addition, there appears a ferromagnetic resonance line due to oxygen defects for samples with Cr ³⁺ concentrations of ≤ 2.5%. Further, in samples with Cr ³⁺ concentrations of ≥ 2.5%, there appears an intense and wide EPR line due to the interactions among the Cr ³⁺ ions in the clusters formed due to rather excessive doping; the intensity and width of this line increase with increasing concentration. The Cr ³⁺ EPR spectra observed in these nanopowders are very different from those in bulk SnO ₂ crystals.