Phase transition and thermal expansion property of Cr2−xZr0.5xMg0.5xMo3O12 solid solution

Abstract

Compounds with the formula Cr2−xZr0.5xMg0.5xMo3O12 (x = 0.0, 0.3, 0.5, 0.9, 1.3, 1.5, 1.7, 1.9) are synthesized, and the effects of Zr4+ and Mg2+ co-incorporation on the phase transition, thermal expansion, and Raman mode are investigated. It is found that Cr2−xZr0.5xMg0.5xMo3O12 crystallize into monoclinic structures for x ≤ 1.3 and orthorhombic structures for x ≥ 1.5 at room temperature. The phase transition temperature from a monoclinic to an orthorhombic structure of Cr2Mo3O12 can be reduced by the partial substitution of (ZrMg)6+ for Cr3+. The overall linear thermal expansion coefficient decreases with the increase of the (ZrMg)6+ content in an orthorhombic structure sample. The co-incorporation of Zr4+ and Mg2+ in the lattice results in the occurrence of new Raman modes and the hardening of the symmetric vibrational modes, which are attributed to the MoO4 tetrahedra sharing corners with ZrO6/MgO6 octahedra and to the strengthening of Mo—O bonds due to less electronegativities of Zr4+ and Mg2+ than Cr3+, respectively.