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Liu H.,Yangzhou University | Zhang Z.,Jianghai College | Zhang W.,Yangzhou University | Chen X.,Yangzhou University | Cheng X.,Jiangsu University
Zhenkong Kexue yu Jishu Xuebao/Journal of Vacuum Science and Technology | Year: 2011

The ZrW2O8 Films with a negative thermal expansion property were deposited by RF magnetron sputtering on Si substrates. The impacts of the deposition conditions, purity of target materials, annealing temperatures and sputtering power, on film quality were evaluated. The microstructures and mechanical properties of the films were characterized with X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and conventional surface probes. The results show that the annealing temperature strongly affects the surface stress distribution of the fairly smooth, compact films with good negative thermal expansion. For example, annealed at 750°C for 3 min, bigger grains with increased pores were observed. The stress uniformly distributes with little variations in the as-deposited films. As the substrate and annealing temperatures increased, the stress, 1.613 GPa at least, its uniform stress distribution deteriorated with an increased bigger stress difference, possibly because of the mismatch of thermal expansion coefficients at the interface of the film and the substrate. Source


Liu H.,China University of Science and Technology | Wang X.,China University of Science and Technology | Zhang Z.,Jianghai College | Chen X.,China University of Science and Technology
Ceramics International | Year: 2012

Y 2-xLa xMo 3O 12 (x=0, 0.5, 2) ceramics were successfully synthesized by the solid state reaction method. The microstructure, composition and thermal expansion property of the resulting samples were investigated by X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and dilatometry. Results indicate that the Y 1.5La 0.5Mo 3O 12 crystallizes in monoclinic Tb 2Mo 3O 12-type structure and it is non-hygroscopic. The Y 1.5La 0.5Mo 3O 12 ceramic is denser than the Y 2Mo 3O 12 and La 2Mo 3O 12 ceramics, and its relative density can reach 94.12% of the theoretical value. Most importantly, it shows almost zero thermal expansion and its thermal coefficient is 0.87×10 -6 K -1 from 178 °C to 600 °C. Y 2Mo 3O 12 ceramic shows negative thermal expansion whereas La 2Mo 3O 12 ceramic shows positive thermal expansion, their thermal expansion coefficients being-12.06×10 -6 K -1 and 8.88×10 -6×10 -6 K -1, respectively. © 2012 Elsevier Ltd and Techna Group S.r.l. Source


Liu H.,China University of Science and Technology | Zhang W.,China University of Science and Technology | Zhang Z.,Jianghai College | Chen X.,China University of Science and Technology
Ceramics International | Year: 2012

A new series of rare earth solid solutions Yb 2-xLa xW 3O 12 were successfully synthesized by the solid-state method. Effects of substituted ion lanthanum on the microstructures and thermal expansion properties in the resulting Yb 2-xLa xW 3O 12 ceramics were investigated by X-ray diffraction (XRD), thermogravimetric analyzer (TGA), field emission scanning electron microscope (FESEM) and thermal mechanical analyzer (TMA). Results indicate that the structural phase transition of the Yb 2-xLa xW 3O 12 changes from orthorhombic to monoclinic with increasing substituted content of lanthanum. The pure phases can form in the composition range of 0 ≤ x < 0.5 with orthorhombic structure and 1.5 < x ≤ 2 with monoclinic one. High lanthanum content leads to a low hygroscopicity of Yb 2-xLa xW 3O 12. Negative thermal coefficients of the Yb 2-xLa xW 3O 12 (0 ≤ x ≤ 2) also vary from -7.78 × 10 -6 K -1 to 2.06 × 10 -6 K -1 with increasing substituted content of lanthanum. © 2011 Elsevier Ltd and Techna Group S.r.l. Source


Zhang Z.,Jianghai College | Zhang W.,China University of Science and Technology | Chen X.,China University of Science and Technology
Ceramics International | Year: 2012

A kind of negative thermal expansion ZrW 2O 8 nanorods were synthesized using a hydrothermal method, followed with a post-annealing at 570 °C for 2 h. Effects of HCl concentration on the microstructure, morphology and negative thermal expansion property in resulting ZrW 2O 8 powders were investigated by X-ray diffraction (XRD) and transmission electron microscope (TEM). Results indicate that the formation of the precursor ZrW 2O 7(OH) 2(H 2O) 2 significantly depends on the HCl concentration, and the precursors ZrW 2O 7(OH) 2(H 2O) 2 can form in the 2-8 mol/L HCl solution. With increasing the concentration of the HCl solutions from 2 to 8 mol/L, the rod-like ZrW 2O 8 particles become more homogeneous, and the average dimension change from 10 μm × 0.5 μm to 700 nm × 50 nm. All the ZrW 2O 8 powders obtained in different conditions exhibit negative thermal expansion property, and the average negative thermal expansion coefficients from 15 °C to 600 °C decrease gradually with the increasing HCl concentration. © 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Source


Liu H.,China University of Science and Technology | Zhang Z.,Jianghai College | Zhang W.,China University of Science and Technology | Zeng X.,China University of Science and Technology | Chen X.,China University of Science and Technology
Ceramics International | Year: 2013

Y2-xLaxW3O12 solid solutions were successfully synthesized by the solid state reaction method. The microstructure, hygroscopicity and thermal expansion property of the resulting samples were investigated by X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM) and thermal mechanical analysis (TMA). Results indicate that the structural phase transition of the Y2-xLaxW3O12 changes from orthorhombic to monoclinic with increasing substituted content of lanthanum. The pure phase can form for 0≤x≤0.4 with orthorhombic structure and for 1.5≤x≤2 with monoclinic one. High lanthanum content leads to a low relative density of Y2-xLaxW3O12 ceramic. Thermal expansion coefficients of the Y2-xLa xW3O12 (0≤x≤2) ceramics also vary from -9.59×10-6 K-1 to 2.06×10-6 K -1 with increasing substituted content of lanthanum. The obtained Y0.25La1.75W3O12 ceramic shows almost zero thermal expansion and its average linear thermal expansion coefficient is -0.66×10-6 K-1 from 103 °C to 700 °C. © 2012 Elsevier Ltd and Techna Group S.r.l. Source

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