Effects of W⁶⁺ occupying Sc³⁺ on the structure, vibration, and thermal expansion properties of scandium tungstate

We experimentally investigate effects of W⁶⁺ occupying the sites of Sc³⁺ in the unit cell of Sc₂W₃O₁₂ (Sc₈W₁₂O₄₈) on the structure, vibration and thermal expansion. The composition and structure of the doped sample (Sc₆W₂)W₁₂O_48±δ (with two W⁶⁺ occupying two sites of Sc³⁺ in the unit cell of Sc₈W₁₂O₄₈) are analyzed and identified by combining the x-ray photoelectron spectroscopy and the synchronous x-ray diffraction with first-principles calculations based on density functional theory. Results show that the crystal with even W⁶⁺ occupying even Sc³⁺ in the unit cell is stable and maintains the orthorhombic structure at room temperature. The structure of the doped sample is similar to that of Sc₂W₃O₁₂, and with even W occupying even positions of Sc in the unit cell and constituting the WO₆ octahedra. Raman analyses show that the doped sample possesses stronger W-O bonds and wider Raman linewidths than those of Sc₂W₃O₁₂. The sample doped with W also exhibits intrinsic negative thermal expansion in the measured range of 150 K-650 K.