M.M. Wu

Synthesis of 1D and heavily doped Zn1−xCoxO six-prism nanorods: improvement of blue–green emission and room temperature ferromagnetism

In this work, one-dimensional (1D) and heavily doped Zn1−xCoxO (x = 0.05, 0.1, 0.15 and 0.2) nanorods (NRs) were successfully fabricated by a new solvothermal method. Such a Zn1−xCoxO nanorod exhibits a hexagonal prism-like microcrystal with a pyramidal top. Analyses from transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) indicated that Zn1−xCoxO NRs possess perfect single crystal wurtzite structures. The influence of Co doping on the structural, optical and magnetic properties of NRs was investigated in detail. It was verified that Co was successfully doped into the ZnO wurtzite lattice structure by X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS). The Zn1−xCoxO NRs show an obvious blue–green emission except for the weak UV emission. The corresponding luminescence mechanism was discussed, and the environment of cobalt in the ZnO wurtzite lattice was also identified through UV-vis spectroscopy. In addition, the magnetic hysteresis (M–H) curves demonstrated that the Zn1−xCoxO NRs possess obvious ferromagnetic characteristics at room temperature. These Zn1−xCoxO NRs are suggested to have potential applications in spintronic, field emission and optoelectronic devices, etc.

Thermal expansion properties of Ln{sub 2-x}Cr{sub x}Mo{sub 3}O{sub 12} (Ln = Er and Y)

Structures and thermal expansion properties of Ln{sub 2-x}Cr{sub x}Mo{sub 3}O{sub 12} (Ln = Er and Y) have been investigated by X-ray powder diffraction. Rietveld analysis results of Ln{sub 2-x}Cr{sub x}Mo{sub 3}O{sub 12} indicate that compounds Er{sub 2-x}Cr{sub x}Mo{sub 3}O{sub 12} (0 {<=} x {<=} 0.3) and Y{sub 2-x}Cr{sub x}Mo{sub 3}O{sub 12} (0 {<=} x {<=} 0.2) crystallize in orthorhombic structure and exhibit negative thermal expansion, while both monoclinic and orthorhombic compounds Er{sub 2-x}Cr{sub x}Mo{sub 3}O{sub 12} (1.7 {<=} x {<=} 2.0) and Y{sub 2-x}Cr{sub x}Mo{sub 3}O{sub 12} (1.8 {<=} x {<=} 2.0) possess positive coefficient of thermal expansion. The coefficients of linear thermal expansion of orthorhombic Ln{sub 2-x}Cr{sub x}Mo{sub 3}O{sub 12} change from negative to positive with increasing chromium content. Thermogravimetric and differential scanning calorimetry have been used to study the hygroscopicity and the phase transition temperature.

Thermal Expansion Behavior of Solid Solution Y1.9R0.1Mo4O15 (R = Sm, Nd, Dy)

Several rare earth solid solutions of Y1.9R0.1Mo4O15 (R=Sm, Nd, Dy) with interesting thermal expansion behavior were prepared and studied by X-ray and neutron diffraction. These solid solutions crystallize in a monoclinic space group P21/c. The lattice parameters a, b and c of Y1.9R0.1Mo4O15 increase with increasing of the ionic radius of substituted elementary. The high-temperature XRD data for Y1.9Sm0.1Mo4O15 show that there is an unusual low thermal expansion behavior in the 25~100°C range followed by a normal thermal expansion at higher temperature up to 600°C. Since no phase transition was observed, the temperature dependence of Mo2-O14 bond distance seems to be responsible for the anomalous thermal behavior.