Yan Jiazhen

Study on Phase Transition Property of Tungsten-doped Vanadium Dioxide Thin Film at Terahertz Range

Vanadium dioxide and tungsten-doped (W-doped) vanadium dioxide thin films deposited by aqueous Sol-Gel method were characterized with several different techniques (i.e. X-ray photoelectron spectroscope, atomic force microscope, X-ray diffraction), to determine their morphology and microstructure. Their metal-to-insulator (MIT) phase transition behavior in infrared spectral region (λ=4 μm) and terahertz (THz) spectral region (0.3–1.0 THz) were observed respectivele. The results demonstrate that the transmittance of W-doped VO 2 film at room temperature is visibly lower than that of undoped VO 2 film in both infrared and terahertz spectral region. The transition temperature of W-doped VO 2 film is also lower than that of undoped VO 2 film in the THz range. The MIT and structural phase transition (SPT) are observed during the phase transition of VO 2 and W-doped VO 2 , and an obvious change of peak position occurs in W-doped VO 2 film.

Effect of Al2O3 Coating on Densification and Aging Sensibility of 3Y-TZP Ceramics

Abstract Al2O3 dopants in amount up to 1.5 wt% were coated on 3-mol-yttria-stabilized zirconia nanopowders adopting heterogeneous precipitation method. The influences of Al2O3 coating on the densification and the aging sensibility of 3Y-TZP were investigated. The process of densification was measured using a dilatometer. The density, the mean grain size and the mechanical properties of the densified 3Y-TZP were tested. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the microstructures of specimens. The results show that the densification of Al2O3-coated zirconia compacts was greatly enhanced by the coating process compared with the conventional co-precipitation process. Dense 3Y-TZP (>6.0 g/cm3) can be obtained using the Al2O3-coated starting powders by pressureless sintering at 1350∼1400 °C. In addition, the aging sensibility of 3Y-TZP is substantially decreased by adding Al2O3. This is probably attributed to the segregation of Al3+ at the grain boundaries of Al2O3-coated 3Y-TZP.

Optical Switching and Color Changing Properties of VO2 Films on Muscovite Substrate

Abstract VO2 films on muscovite substrate were fabricated by inorganic sol-gel method and the following thermal treatment. The films were characterized by X-ray diffraction, scanning electron microscope (SEM), fourier transform infrared spectrophotometer (FTIR) and color difference (ΔE*). The FTIR result shows that the film has an infrared transmittance switching efficiency of 77% in the metal-insulator transition. The color changing properties indicate that the film color reversibly changes from khaki to yellow-green as the temperature changes. The relationship between ΔE* and the temperature presents a hysteresis loop, which is in accordance with the infrared optical switching properties. The maximum of ΔE* during the film metal-insulator transition is 11.31.

TiO 2 中间层对基于溶胶–凝胶法制备的VO 2 薄膜光学特性的影响

为了提高VO 2 薄膜的热致相变性能, 采用复合结构与掺杂相结合的方法, 首先通过溶胶-凝胶法在云母基底上制备锐钛型TiO 2 薄膜, 再在光致亲水性处理的TiO 2 /云母基底上涂覆V 2 O 5 以及掺钨V 2 O 5 水溶胶, 然后经热处理获得VO 2 /TiO 2 及V x W 1- x O 2 /TiO 2 复合薄膜. 采用X射线衍射仪(XRD)、场发射扫描电子显微镜(FESEM)、傅立叶变换红外光谱仪(FTIR)研究薄膜的物相, 表面形貌以及热致相变特性. 结果表明, VO 2 /TiO 2 复合薄膜晶体生长为(011)面择优取向; V x W 1- x O 2 /TiO 2 复合薄膜产生多种取向. TiO 2 中间层有助于使VO 2 薄膜生长致密, 相变温度降低, 更使V x W 1- x O 2 /TiO 2 复合薄膜滞后温宽降至约4℃.为了提高VO 2 薄膜的热致相变性能, 采用复合结构与掺杂相结合的方法, 首先通过溶胶–凝胶法在云母基底上制备锐钛型TiO 2 薄膜, 再在光致亲水性处理的TiO 2 /云母基底上涂覆V 2 O 5 以及掺钨V 2 O 5 水溶胶, 然后经热处理获得VO 2 /TiO 2 及V x W 1- x O 2 /TiO 2 复合薄膜。采用X射线衍射仪(XRD)、场发射扫描电子显微镜(FESEM)、傅立叶变换红外光谱仪(FTIR)研究薄膜的物相、表面形貌以及热致相变特性. 结果表明, VO 2 /TiO 2 复合薄膜晶体生长为(011)面择优取向; V x W 1- x O 2 /TiO 2 复合薄膜产生多种取向。TiO 2 中间层有助于使VO 2 薄膜生长致密, 相变温度降低, 更使V x W 1- x O 2 /TiO 2 复合薄膜滞后温宽降至约4℃。