Structure, Phase Transition, and Controllable Thermal Expansion Behaviors of Sc_(2?x)Fe_xMo_3O_(12)

摘要

The crystal structures, phase transition, and thermal expansion behaviors of solid solutions of Sc_(2?x)FexMo_3O_(12) (0 ≤ x ≤ 2) have been examined using X-ray diffraction (XRD), neutron powder diffraction (NPD), and differential scanning calorimetry (DSC). At room temperature, samples crystallize in a single orthorhombic structure for the compositions of x < 0.6 and monoclinic for x ≥ 0.6, respectively. DSC results indicate that the phase transition temperature from monoclinic to orthorhombic structure is enhanced by increasing the Fe~(3+) content. Hightemperature XRD and NPD results show that Sc_(1.3)Fe_(0.7)Mo_3O_(12) exhibits near zero thermal expansion, and the volumetric coefficients of thermal expansion derived from XRD and NPD are 0.28 × 10~(?6) °C~(?1) (250?800 °C) and 0.65 × 10~(?6) °C~(?1) (227?427 °C), respectively. NPD results of Sc_2Mo_3O_(12) (x = 0) and Sc_(1.3)Fe_(0.7)Mo_3O_(12) (x = 0.7) indicate that Fe substitution for Sc induces reduction of the mean Sc(Fe)?Mo nonbond distance and the different thermal variations of Sc(Fe)?O5?Mo2 and Sc(Fe)?O3?Mo2 bond angles. The correlation between the displacements of oxygen atoms and the variation of unit cell parameters was investigated in detail for Sc_2Mo_3O_(12).