Effects of (KMn)³⁺ substitution on phase transition and thermal expansion property of Fe₂Mo₃O₁₂

In this work, a series of (KMn)(x)Fe2-xMo3O12 (0 <= x <= 1) ceramics were prepared using a solid-state reaction. The effects of (KMn)(3+) substitution on phase transition and thermal expansion behavior of Fe2Mo3O12 were investigated. Results indicate that Fe3+ cations can be partially substituted by (KMn)(3+) in Fe2Mo3O12. As increasing (KMn)(3+) substitution, the monoclinic Fe2Mo3O12 gradually transforms into monoclinic (KMn)(x)Fe2-xMo3O12. For 0.4 <= x <= 0.75, single phase (KMn)(x)Fe2-xMo3O12 solid solutions with the monoclinic structure were obtained. When x = 1, (KMn)(3+) reached its solid solubility limit in Fe2Mo3O12 and MnMoO4 impurity was detected. (KMn)(3+)-substitution can effectively reduce the phase transition temperature from 508.1 to 162.9 degrees C, widen the negative thermal expansion (NTE) response temperature range, and improve the NTE performance of Fe2Mo3O12 ceramics. Monoclinic (KMn)(0.75)Fe1.25Mo3O12 ceramics present the best NTE performance, and its corresponding coefficient of thermal expansion (CTE) is -9.79 x 10(-6) degrees C-1 in 200-600 degrees C