Vacancy contents in MnZn ferrites from TG curves

Expressions for calculating the cation vacancy contents of MnZn ferrites from thermogravimetric curves are presented together with some experimental data. In a single-phase MnZn ferrite synthesized by conventional ceramic procedures, the O-2 evolution accompanying ferrite formation follows the formal equation. [GRAPHICS] where alpha and beta denote the MnO and ZnO mole fractions in the primary mixture gamma=alpha+beta, theta and phi depend on the quantities of Fe2+ and Mn3+ formed, respectively, phi=theta-phi and sigma'/sigma is a function of the former parameters. Even though the relative amounts of Fe2+/Fe3+ and Mn2+/Mn3+ remain uncertain, the vacancy content [V] of the ferrite can be determined because it depends on phi alone, which is related to the change in mass of the sample as the synthesis takes place through the equation phi=(1.5-gamma)mu(beta)/mu(O2)(1-m(f)/m(i)) Here, m(i) and m(f) are the masses of the sample before and after O-2 evolution, mu(B) is the formula mass of the ferrite and mu(O2) is the O-2 molar mass. Practically vacancy-free single-phase MnZn ferrite samples were obtained by sintering in air at 1250 degrees C and cooling in pure N-2.