THERMAL-BEHAVIOR AND CATION DISTRIBUTION OF SUBMICRON COPPER FERRITE SPINELS CUXFE3-XO4 LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.5) STUDIED BY DTG, FTIR, AND XPS

The valence state and the cation distribution on octahedral (B) and te trahedral (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 invest igated: It was demonstrated that Cu-B(+), Fe-B(2+), and Cu-A(+) oxidiz e 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 ea ch oxidizable cation. A quantitative analysis by DTG based on this dif ference of reactivity only permits one to determine the concentration of B-site (Fe2+ + Cu+) ions and A-site Cu+ ions. Using TG analysis per formed on different experiments varying the oxygen partial pressure, t he 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. a lpha = 0.50 and beta = 0.20 for x = 0.32, From FTIR and XPS data, it h as been shown that when the deviation from stoichiometry is the greate st the vacancies and all the Cu2+ ions are on B-sites. (C) 1996 Academ ic Press, Inc.