Vacancy Contents in MnZn Ferrites From TG Curves

Abstract

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 Zn_σβ Fe³⁺ _2σ(1–γ) [V ]_{σ/4(1–2γ)} O₄ =σ'/σ Mn²⁺ _σ(α–2ϕ) Zn_σβ 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) µ_β /µ_O2 (1–m _f /m _i )

Here, m _i and m _f are the masses of the sample before and after O₂ evolution, µ_B is the formula mass of the ferrite and µ_O2 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 .