D. Aymes

Inelastic neutron scattering due to acoustic vibrations confined in nanoparticles: Theory and experiment

The inelastic scattering of neutrons by nanoparticles due to acoustic vibrational modes (energy below 10 meV) confined in nanoparticles is calculated using the Zemach-Glauber formalism. Such vibrational modes are commonly observed by light-scattering techniques (Brillouin or low-frequency Raman scattering). We also report high-resolution inelastic neutron-scattering measurements for anatase

Experimental set up for determining the temperature—oxygen partial pressure conditions during synthesis of spinel oxide nanoparticles

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Correlation Between the Reactivity Towards Oxygen and the Coercitivity in Submicron Vanadium Ferrite Spinels

nanoparticles in a loose powder. Factors enabling the observation of such vibrations are discussed. These include a narrow nanoparticle size distribution which minimizes inhomogeneous broadening of the spectrum and the presence of hydrogen atoms oscillating with the nanoparticle surfaces which enhances the number of scattered neutrons.

Influence of grain size, oxygen stoichiometry, and synthesis conditions on the γ-Fe2O3 vacancies ordering and lattice parameters

Abstract Nanometric spinel oxide powders, Fe 3− x M x O 4 , where M is a transition element, have been synthetized by soft chemistry. This method generally leads to a non-stoichiometric phase, Fe 3− x M x O 4+δ where δ is the deviation from stoichiometry so that further annealing at low temperatures around 450°C and low oxygen partial pressure around 10 −25 Pa given by N 2 /H 2 /H 2 O gas mixtures is required: this enables a stoichiometric compound to be obtained and a nanometric size to be maintained. The complete set up consisting of a gas mixer, a thermogravimetric apparatus and a preparative furnace is described. Some results concerning the conditions of temperature and oxygen partial pressure leading to stoichiometry are given in the case of vanadium ferrites containing or without Co.

Spark plasma sintering of cobalt ferrite nanopowders prepared by coprecipitation and hydrothermal synthesis

Nanometric powders of Fe 2 VO 4 and Fe 1.84 V 0.92 Co 0.23 O 4 have been synthetised by chimie douce process The cations in the spinel structure can oxidize at low temperatures without any phase transformation leading to cation-deficient spinel with formula Fe 2 VO 4+δ and Fe 1.84 V 0.92 Co 0.23 O 4+δ , where δ is the deviation from stoichiometry, due to a change of the anion-cation ratio, consecutive to formation of vacancies. The oxidation, investigated by thermogravimetry, involves several stages, each stage corresponding to the oxidation of one oxidizable cation, Fe 2+ , V 2+ ,V 3+ on B (octahedral) or A (tetrahedral) sites. Coercivity has also been studied, revealing that the coercive field increases with the rate of oxidation.