Lattice parameters and site occupancy factors of magnetite–maghemite core–shell nanoparticles. A critical study

Abstract

The size-driven expansion and oxidation-driven contraction phenomena of nonstoichiometric magnetite-maghemite core-shell nanoparticles have been investigated by the total scattering Debye function approach. Results from a large set of samples are discussed in terms of significant effects on the sample average lattice parameter and on the possibility of deriving the sample average oxidation level from accurate, diffraction-based, cell values. Controlling subtle experimental effects affecting the measurement of diffraction angles and correcting for extra-sample scattering contributions to the pattern intensity are crucial issues for accurately estimating lattice parameters and cation vacancies. The average nanoparticle stoichiometry appears to be controlled mainly by iron depletion of octahedral sites. A simple law with a single adjustable parameter, well correlating lattice parameter, stoichiometry and size effects of all the nanoparticles present in the whole set of samples used in this study, is proposed. research papers

A total scattering Debye function analysis study of faulted Pt nanocrystals embedded in a porous matrix

“…X-ray data were also collected on the empty capillary and for the environment (i.e. air/He flux), under the same experimental conditions, in order to subtract these extra-sample signals from those of the Pt@SiO 2 and MCM-41 samples, after appropriate absorption correction (Cervellino et al, 2014) (see Fig. 1).…”

“…7(b). The second term in equation (7) can be easily approximated by the ½1 À ð=DÞ one, previously proposed by Cervellino et al (2014) for iron oxide nanoparticles, where = 4/3B, and B being the surface tension and the bulk modulus, respectively. In this case, taking B = 277 GPa (Ono et al, 2011) and = 2 , a positive surface tension value = 1.45 N m À1 is computed, in line with values reported for Pt nanoparticles (Gelisio & Scardi, 2014) and for liquid Pt at its melting point [ = 1.80 N m À1 (Paradis et al, 2014)].…”

Hypericin-bearing magnetic iron oxide nanoparticles for selective drug delivery in photodynamic therapy

“…In comparison with literature values for magnetite (a=0.83967 nm) and maghemite (a=0.83457 nm), the lattice parameter is located right between both iron oxide forms. 37 Based on this result, a definite determination, whether magnetite or maghemite is formed, cannot be done. However, it can be assumed that a mixture of both is present in the sample.…”

Ligand-induced symmetry breaking, size and morphology in colloidal lead sulfide QDs: from classic to thiourea precursors

“…PDF-derived values (green stars) confirm the same behaviour and are in line with those provided by DSE on the same TMS-1 CQDs. In analogy to the size-dependent lattice expansion found in oxide nanoparticles and attributed to negative surface pressure effects [34], the dependence of a fcc on the QDs diameter D of overlaps to that proposed in ref. [17] (red dashed curve, obtained by fitting the green squares only).…”

“…All datasets were collected in the 0.5°-130° 2θ range (Q = 0.1-19 Å -1 ) using a single-photon counting Silicon microstrip detector (MYTHENII) [45]. Angle dependent intensity absorption corrections were applied to the raw data and to the air and capillary scattering contributions, independently measured on the empty container and the background; the latter were properly subtracted from the scattering of the sample [34]. Data of pure toluene and hexane were separately collected, in the same experimental conditions, and underwent the same data reduction procedure, to be used as part of the model (vide infra).…”