X-ray Absorption Investigation of the Formation of Cobalt Ferrite Nanoparticles in an Aerogel Silica Matrix

Abstract

X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) techniques at both Fe and Co K-edges were used to investigate the formation of CoFe 2 O 4 nanoparticles embedded in a silica aerogel matrix as a function of calcination temperature and CoFe 2 O 4 content. In particular, nanocomposite aerogels containing relative CoFe 2 O 4 amounts of 5 and 10 wt % and calcined at 450, 750, and 900°C were studied. The evolution of the nanophase with calcination temperatures depends on the composition. In the sample containing 10 wt % of nanophase, results indicate that CoFe 2 O 4 nanocrystals were formed after calcination at 750°C, whereas in the sample containing 5 wt % of nanophase, they were obtained only after calcination at 900°C. Quantitative determination of the distribution of the iron and cobalt phase in the octahedral and tetrahedral sites of the spinel structure shows that cobalt ferrite prepared by sol-gel has a partially inverted spinel structure with a degree of inversion around 0.70.

Structural and vibrational properties of Co nanoparticles formed by ion implantation

“…For the bulk standards and two concentration extremes ͑0.3 and 9.0 at. 27,28 For the low-concentration, unannealed samples, the XANES spectrum is similar to that of Co 3 O 4 , including the shift to higher energy, as consistent with Fukimi 29 and Cattaruzza et al, 30 who reported that Co atoms in an as-implanted/as-deposited, NP-free state prefer a tetrahedral arrangement in SiO 2 similar to that in Co 3 O 4 . 5, while the fcc, hcp, and oxide fractions are shown in Fig.…”

X-ray absorption fine structure study of amorphous metal oxide thin films prepared by photochemical metalorganic deposition

“…7(a,b). The determined Co-O distance of 1.98Å is intermediate between the Co-O distances expected for a partially inverted spinel (with distances of 1.89-1.92 and 2.06-2.07Å for tetrahedral and octahedral sites, respectively) [97,98]. The Co-metal second-neighbor shell distance of 2.96Å is in good agreement with the 2.95Å reported by Carta and coworkers [97].…”

“…Furthermore, Nilsen et al [103] measured EXAFS on nanoparticulate CoFe 2 O 4 grown hydrothermally and observed Co-O distances of 2.02(1) and 2.05(7)Å in samples with particle sizes of 16 and 39 nm, respectively. The difference between the Fe-O and Co-O distances in the amorphous samples are representative of the difference in ionic radii for the two elements [104], and comparable to the Fe-O and Co-O distances determined by EXAFS for octahedral sites in CoFe 2 O 4 [97]. Hence, it is not unreasonable to conclude that the amorphous result is consistent with the inverse spinel structure.…”

Hydrothermal stability investigation of micro- and mesoporous silica containing long-range ordered cobalt oxide clusters by XAS

“…42 A very weak pre-edge peak was observed for CoO due to its octahedral coordination environment 43,44 for cobalt atoms in the first shell. For cobalt, XANES spectra typically show a more distinct pre-edge where Co is present in tetrahedral (T d ) environments, whereas in the case of octahedral (O h ) coordination the pre-edge is less prominent.…”