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 O2 evolution accompanying ferrite formation follows the formal equation.
Mn2+σα Znσβ Fe3+2σ(1–γ) [V ]σ/4(1–2γ) O4 =σ'/σ Mn2+σ(α–2ϕ) Znσβ Fe2+2σθ Mn3+2σϕ Fe3+2σ(1–γ–θ) [V ]σ/4(1–2γ–3ϕ) O4 +σ'φ/2O2 (g)
where α and β denote the MnO and ZnO mole fractions in the primary mixture γ=α+β, θ and ϕ depend on the quantities of Fe2+ and Mn3+ formed, respectively, φ=θ–ϕ and σ'/σ 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 φ alone, which is related to the change in mass of the sample as
the synthesis takes place through the equation
φ=(1.5–γ) µβ /µO2 (1–mf /mi )
Here, mi and mf are the masses of the sample before and after O2 evolution, µB is the formula mass of the ferrite and µO2 is the O2 molar mass. Practically vacancy-free single-phase MnZn ferrite samples were obtained by sintering in air at 1250°C and cooling
in pure N2 .