Effects of W^(6+) occupying Sc^(3+) on the structure, vibration, and thermal expansion properties of scandium tungstate

We experimentally investigate effects of W^(6+)occupying the sites of Sc^(3+)in the unit cell of Sc_(2) W_(3) O_(12)(Sc_(8) W_(12) O_(48))on the structure, vibration and thermal expansion. The composition and structure of the doped sample(Sc_(6) W_(2))W_(12) O_(48±δ)(with two W^(6+)occupying two sites of Sc^(3+)in the unit cell of Sc_(8) W_(12) O_(48)) 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 W^(6+)occupying even Sc^(3+)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 Sc_(2) W_(3) O_(12), and with even W occupying even positions of Sc in the unit cell and constituting the WO_(6) octahedra. Raman analyses show that the doped sample possesses stronger W–O bonds and wider Raman linewidths than those of Sc_(2) W_(3) O_(12). The sample doped with W also exhibits intrinsic negative thermal expansion in the measured range of 150 K–650 K.