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

Compounds with the formula Cr_2−xZr_0.5xMg_0.5xMo₃O₁₂ (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 Cr_2−xZr_0.5xMg_0.5xMo₃O₁₂ 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. [ABSTRACT FROM AUTHOR]