Wu Meimei

Superconductivity Tuned by the Iron Vacancy Order in KxFe2−ySe2

Combining in-depth neutron diffraction and systematic bulk studies, we discover that the √5 × √5 Fe vacancy order, with its associated block antiferromagnetic order, is the ground state with varying occupancy ratios of the iron 16i and vacancy 4d sites across the phase-diagram of KxFe2−ySe2. The orthorhombic order, with one of the four Fe sites vacant, appears only at intermediate temperatures as a competing phase. The material experiences an insulator to metal crossover when the √5 × √5 order is highly developed. Superconductivity occurs in such a metallic phase.

Thermal expansion properties of Lu2−x FexMo3O12

The structures and thermal expansion properties of Lu2−xFexMo3O12 have been investigated by X-ray diffraction (XRD). XRD patterns at room temperature indicate that compounds Lu2−xFexMo3O12 with x ≤ 1.3 exhibit an orthorhombic structure with space group Pnca; compounds with x = 1.5 and 1.7 have a monoclinic structure with space group P21/a. Studies on thermal expansion properties show that the linear thermal expansion coefficients of orthorhombic phase vary from negative to positive with increasing Fe content. Attempts to make zero thermal expansion materials indicate that zero thermal expansion can be observed in Lu1.3Fe0.7Mo3O12 in the temperature range of 200–400 °C.

Thermal expansion properties and hygroscopicity of Y2−x Sm x W3O12 (x = 0.0–0.4) compounds

A novel class of solid solutions of Y2−xSmxW3O12 (x = 0.0−0.4) were synthesized and studied by means of powder X-ray diffraction. All samples crystallize in an orthorhombic space group Pnca. The lattice parameters a, b and c of Y2−xSmxW3O12 increase with increasing Sm content. Since the compounds of this series hydrate at room temperature, thermogravimetric (TG) analysis was carried out. The result shows that the compound stores less water with increasing Sm content. The thermal expansion properties of Y2−xSmxW3O12 (x = 0.1, 0.3 and 0.4) were investigated with high temperature X-ray diffraction. Negative thermal expansion coefficient αI becomes less negative from −6.644×10−6 to −6.211×10−6°C−1 when x changes from 0.1 to 0.4.