Oxygen Isotope Exchange in Nanocrystal Oxides

Abstract

Investigations on bulk samplesMost often, OIE studies on bulk samples involve isothermal annealing of samples in oxygen (or other oxygen-containing gas) enriched with 18 О isotope and measurement of

Isotope Exchange between ¹⁸O₂ Gas and Mechanoactivated Oxides of the Family Rare Earth – Manganese – Oxygen

“…Let us note two important points related to the use of expressions such as (1). At first, it was established [6] that the values of the particle radius r in (1) were close to the average size of coherent scattering regions experimentally determined by X-ray diffraction analysis. It means that molecules or atoms of 18 О oxygen almost freely penetrate into the space between nano-sized particles.…”

“…1 corresponds to the case when the bulk oxygen diffusion in the oxide particles is negligible. In this case, the time variation of the average concentration of 18 O isotope C(t) in the samples is due to isotopic exchange between gaseous oxygen 18 O 2 and the outer atomic layer of the oxide particles; the corresponding theoretical expression upon condition of free access of oxygen molecules to the particles surface has a form [6]:…”

“…In this regard, the present study deals with the bulk diffusion of tracer oxygen in undoped manganites of rare earth metals RMnO 3+δ (LaMnO 3+δ , NdMnO 3+δ , SmMnO 3+δ ) at low temperatures. The procedure described in the works [6,7] has been used to measure the low values of the diffusion coefficients. It is based on the study of the kinetics of oxygen isotope exchange between gaseous oxygen 18 O 2 and micro-and nanopowder oxides.…”

Mechanical Activation of Mn-O Oxides: Structural Phase Transitions, Magnetism and Oxygen Isotope Exchange

“…It was found that mechano-activation of oxides MnO, Mn 2 O 3 Mn 3 O 4 and MnO 2 substantially activates processes of their interaction with the gas phase. The models for the description of experimental data on the kinetics of isotopic exchange were suggested, the frequency of the isotopic exchange of oxides with the gas phase on the surface were set, and new data on the volume diffusion coefficients D V of oxygen in the manganese oxides were obtained [20][21][22][23]. The obtained values of the pre-exponential factor in D V for oxides Mn 2 O 3, Mn 3 O 4 [21] indicate a very low concentration of structural vacancies in them.…”

Application of nuclear reaction analysis to studying hydrogen diffusion and nonstoichiometry in metal oxides

“…В последнее время было выполнено несколько работ, в которых для исследования водородной и кислородной подсистем оксидов была применена ускорительная методика ядерного микроанализа (NRA). С ее помощью были получены данные о кислородном и водородном изотопном обмене и коэффициентах диффузии атомов кислорода и дейтерия в оксидах [1][2][3]. Кроме того, для проведения исследований по поверхностной стехиометрии оксидов и диффузии в них дейтерия были разработаны две оригинальные методики, основанные на применении NRA.…”