Abstract
The diagrams of the concentrations of point defects, determined for a series of temperatures, for the oxides: Mn1-deltaO, (1173-1830 K), Co1-deltaO (1223-1673 K) and Ni1-deltaO (1273-1673 K), whilst taking into consideration simple defects and defect clusters of type (2:1), (4:1), (6:2), are presented in this work. A new method was used for the calculations of the diagrams and the results of the studies of the deviation from the stoichiometry obtained by many authors were used in the calculations. The values of DGo of the formation of the individual defects and clusters were determined; their temperature dependencies were also determined. The calculations show that in the studied oxides the maximal concentration of defect clusters is lower than the concentration of single-ionized cation vacancies. At the lowest temperatures studied, the concentration of clusters is comparable to the concentration of electroneutral vacancies. The ratio of these concentration decreases with the temperature increase. The presence of defect clusters only slightly decreases the concentration of cation vacancies. The ratio of the concentrations of defect clusters varies with the temperature. This ratio is different for the individual oxides.
Highlights
The non-stoichiometric oxides of 3d transition metals: Mn1-δO, Fe1-δO, Co1-δO and Ni1-δO have been the subject of numerous studies for many years, due to their potential use and because they are model systems that allow for the verification of the point defects theory (Kröger, 1974; Kofstad, 1972; Rao & Raveau, 1995; Smyth, 2000; Sørensen, 1981; Tilley, 2008)
At higher concentrations of defects, for example in Co1-δO and Mn1-δO oxides, there is a mutual interaction between the vacancies and the electron holes, and a significant contribution to the deviation from the stoichiometry is due to the single-ionized vacancies and electroneutral vacancies (these defects could be considered as complexes of a cation vacancy and M3+ (M M ) ion
During the calculations of the concentrations of defects it was assumed, according to the point defects theory, that point defects are treated as quasi-particles that form a solution in the oxide and are subject to classical laws of chemical thermodynamics
Summary
The non-stoichiometric oxides of 3d transition metals: Mn1-δO, Fe1-δO, Co1-δO and Ni1-δO have been the subject of numerous studies for many years, due to their potential use and because they are model systems that allow for the verification of the point defects theory (Kröger, 1974; Kofstad, 1972; Rao & Raveau, 1995; Smyth, 2000; Sørensen, 1981; Tilley, 2008). They show a real insufficiency of metal and the defects are present mainly in the cation sublattice. Dieckmann (Dieckmann, 1977), Nowotny et al (Nowotny et al, 1984, 1989, 1992) and ISSN 1916-9698 E-ISSN 1916-9701 www.ccsenet.org/ijc
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