Tailored phase transition temperature and negative thermal expansion of Sc-substituted Fe2Mo3O12 synthesized by the co-precipitation method

Abstract

A new series of Fe2-xScxMo3O12 (x = 0, 0.4, 0.8, 1.2, 1.6) ceramics have been synthesized by the co-precipitation reaction method. The phase composition, microstructure, phase transition and thermal expansion behavior of the Fe2-xScxMo3O12 samples have been investigated using XRD, Raman, SEM, STEM, EDX, XPS and TMA. Results show that Fe3+ has been substituted by Sc3+ successfully. Single phase Fe2-xScxMo3O12 with Fe2Mo3O12-type monoclinic structure can be synthesized when 0 ≤ x ≤ 0.8. Fe2-xScxMo3O12 consisting of two phases with monoclinic and orthorhombic structures is found when x = 1.2 and will be completely transformed to Sc2Mo3O12-type orthorhombic structure when x = 1.6. Monoclinic-to-orthorhombic phase transition temperature of Fe2-xScxMo3O12 can be successfully reduced from 513 °C to below room temperature with increasing Sc3+-substitution content (x). The temperature range of Fe2-xScxMo3O12 showing negative thermal expansion can be significantly expanded. Moreover, Fe0.4Sc1.6Mo3O12 ceramics with orthorhombic structure displays stable negative thermal expansion property from 25 °C to 600 °C and its average linear coefficient of thermal expansion is measured to be −5.80 × 10−6 °C−1.