Cation distribution in ultrafine cadmium ferrite particles determined by X-ray diffraction

Cation distribution, oxygen parameter and thermal parameter for bulk material and fine particles of CdFe₂O₄ were determined by X-ray powder diffraction based on the relation between ln(I^obs/I^cal) and sin²θ/λ², where I^obs is the observed intensity, I^cal is the calculated intensity, θ is the Bragg angle, and λ is the X-ray wavelength. The occupancy of Fe³⁺ ions at the A-sites is 0.06 and 0.13 for bulk material and fine particles with a size of ∼7 or ∼8 nm, respectively. The cluster consisting of small number of Fe³⁺ ions at the B-sites are formed around a Fe³⁺ ion at the A-site through the A-B interactions. The oxygen parameters of the fine particles with size of ∼7 and ∼8 nm and the bulk material are 0.385, 0.389 and 0.391, respectively. The thermal parameters of the fine particles are approximately eighty times larger than that of the bulk material. The enhanced thermal parameter can be explained in terms of the softening on the surface.