Thermal behavior and cation distribution of submicron copper ferrite spinels CuxFe3-xO4 (0<=x<=0.5) studied by DTG, FtIR, and XPS

The valence state and the cation distribution on octahedral (B) and tetrahedral (A) sites in the spinel structure of Cu and Fe ions has been determined in nanometric copper-substituted magnetites, CuxFe3-xO4 (0 less than or equal to x less than or equal to 0.5), by TG, DTG, FTIR, and XPS, The oxidation of the oxidizable cations has also been investigated: It was demonstrated that Cu-B(+), Fe-B(2+), and Cu-A(+) oxidize into Cu2+ and Fe3+ ions below 300 degrees C. Moreover, the stability of each cation toward oxidation, decreasing from Cu-B(+) to Cu-A(+), has been found in close relation with the cation-oxygen distance of each oxidizable cation. A quantitative analysis by DTG based on this difference of reactivity only permits one to determine the concentration of B-site (Fe2+ + Cu+) ions and A-site Cu+ ions. Using TG analysis performed on different experiments varying the oxygen partial pressure, the cationic distribution has been obtained, It is given by the formula (Cualpha xFe1-alpha x3+)(A) (Cu((1-alpha-beta)x)(3+)Cu(beta x)(+)Fe(1+(2 alpha+beta)x)(2+))B O-4(2-), where alpha and beta varies with x. alpha = 0.50 and beta = 0.20 for x = 0.32, From FTIR and XPS data, it has been shown that when the deviation from stoichiometry is the greatest the vacancies and all the Cu2+ ions are on B-sites. (C) 1996 Academic Press, Inc.