Room-temperature mechanochemical synthesis of RE molybdates: Impact of structural similarity and basicity of oxides

The feasibility of room-temperature synthesis of R₁₀Mo₂O₂₁ (R = La, Y, Er) molybdates via mechanochemical processing of the 5R₂O₃+2MoO₃ oxide mixtures has been studied using X-ray powder diffraction (XRD) with Rietveld refinement and electron spin resonance spectroscopy (ESR). In all systems, the initial stage of mechanochemical synthesis is associated with MoO₃ dissolution in R₂O₃ despite the difference in the crystal structure of initial oxides: La₂O₃ ((Formula presented.), no. 164), Er₂O₃ and Y₂O₃ ((Formula presented.), no. 206). Only for the 5Er₂O₃ + 2MoO₃ system containing magnetic cations, ESR detects A-type Mo⁵⁺ centers, thus enabling to follow the decrease in MoO₃ content during room-temperature mechanochemical synthesis. In the Er- and Y-based systems, the starting oxides and synthesized R₁₀Mo₂O₂₁ (R = Y, Er) molybdates have the same bixbyite structure and mechanochemical MoO₃ dissolution in these oxides leads to R₁₀Mo₂O₂₁ synthesis at room temperature within 80 min. In the La-based system, MoO₃ dissolution leads mainly to mechanochemical synthesis of La₁₀Mo₂O₂₁ with the same structure as the starting La₂O₃ ((Formula presented.), no. 164), but the amorphization of La₂O₃ and formation of basic lanthanum hydroxide during milling also took place. The use of nanosized MoO₃ facilitates the slightly formation of La₁₀Mo₂O₂₁ ((Formula presented.), no. 164), but makes no impact on the synthesis of La₁₀Mo₂O₂₁ ((Formula presented.) (RI), no. 166).