VOC2O4·H2O热分解制备纳米VO2粉体及相变特性

提出了一种采用草酸氧钒(VOC2O4·H2O)热分解制备纳米VO2的方法.通过热分析(TG-DSC)、XRD和TEM手段,分析了草酸氧钒前驱体的热分解过程,纳米VO2的结构和形貌,测定了纳米VO2粉体的电阻-温度曲线.实验结果表明VOC2O4·H2O热分解开始温度为343℃,在380℃,真空度为20～50Pa的条件下,热分解获得VO2的平均尺寸为22nm,相变温度为69℃.     

VO2薄膜的制备及其热致相变特性研究

以双氧水和V2O5粉末为前驱体制备出V2O5溶胶,然后在云母基底上成膜,通过后续热处理退火得到优异相变性能的VO2薄膜。采用SEM、XRD分析薄膜形貌和微观结构,利用FT-IR等检测薄膜的光学性质。实验表明,VO2薄膜在云母基底上沿(011)晶面择优取向生长,颗粒生长致密且大小分布均匀。薄膜具有优异的相变陡然性,相变温度及滞后温宽都较低。在红外波段,相变前后透过率及反射率变化都较大,对红外光调节性能较好;在可见光波段,薄膜在相变前后都具有较高可见光透过率。     

热致VO2薄膜在激光防护方面的应用研究

VO2是一种固态热致变色材料,它的晶态结构可以在半导体-金属-绝缘体之间可逆转变。介绍了VO2的相变特性,研究了氧化钒的相变机理。根据激光对光电探测器的损伤机理,研究了氧化钒薄膜对激光的智能防护,并对其进行了计算和分析。结果表明,当一束激光照射VO2薄膜防护的探测器时,VO2薄膜可以在激光对探测器造成损伤之前完成相变,从而保护探测器,因此可用于探测器针对强激光的智能防护。     

射频磁控溅射纳米二氧化钒薄膜的电致相变特性

采用射频磁控溅射方法和热处理工艺制备了二氧化钒（VO2）薄膜,并制作了金属钨／VO2／金属钨三明治结构,通过改变金属钨／VO2／金属钨三明治结构中VO2薄膜与金属钨电极的接触面积,研究了VO2薄膜的电致相变特性．采用x射线衍射仪（XRD）、扫描电子显微镜（SEM）、四探针和半导体参数测试仪对VO2薄膜的结晶取向、表面形貌、方块电阻和,I-V特性进行了测试．实验结果表明,所制备的VO2薄膜为具有热致相变特性的单一组分VO2纳米薄膜,在热激励下,薄膜的方块电阻相变幅度达到2个数量级;在电压的激励下,VO2薄膜与金属钨的接触面积为12μm×12um时,电流发生跳变的阁值电压为9．4V,随着接触面积的减小,闽值电压也逐渐降低．     

VO2热致变色智能窗:现状、挑战及展望

二氧化钒(VO2)作为一种过渡金属氧化物,能够响应外界温度变化并发生半导体–金属相变,相变过程中伴随着红外波段透过率的大幅度改变,在智能窗领域受到广泛关注。近年来,关于VO2制备方式、相变机理以及改善调光能力等方面的研究颇为丰富。然而,在实际应用中仍面临技术瓶颈和挑战,如本征相变温度较高、可见光透过率较低、太阳能调节效率不足、耐候稳定性较差、颜色舒适度较低(呈现棕黄色)等。目前,关于VO2本身性能改善的研究已有很多,提升其性能的通用手段如元素掺杂、多层膜结构设计、微结构设计等已被广泛采用。本文总结了VO2通用性能的提升策略,着重介绍了VO2基智能窗在实际应用中服役性能、低温柔性制备以及颜色调控等方面的最新研究进展,同时从皮肤舒适性和环境友好性等方面分析和展望了未来的发展。     

热致变色VO2薄膜的制备及光学性能研究

利用等离子体发射光谱监测系统(PEM)控制钒的等离子强度,在石英基底上磁控溅射制备了VO2薄膜。采用XRD、XPS、SEM、紫外-可见-近红外分光光度计及傅立叶红外分光光度计研究薄膜的结构、光学及相变特性。结果表明,所制备的VO2薄膜具有(011)取向,VO2薄膜的热滞回线宽度为25℃,可见光透过率和太阳光调节率分别可达Tlum,l=34.1%、Tlum,h=35.3%和ΔTsol=6.8%,相变前后,红外光区的反射率变化最大值可达44.4%。     

二氧化钒薄膜制备及其相变机理研究分析

VO2是一种固态热致变色材料，随着温度的变化它的晶态结构会从半导体态相变到金属态，而且相变可逆。由于相变前后电、磁、光性能有较大的变化，这使得它成为一种有前景的电／光转换、光存储、激光保护和智能窗材料。本综述VO2膜的制取方法及相变机理的研究进展。     

VO2薄膜相变温度调节方法及机理

VO_2是一种相变温度为68℃(接近室温)的热致相变材料,具有十分广泛的潜在应用价值。但68℃相较于环境温度仍显得较高,而且不同的应用环境对相变温度有不同的需求,因此针对VO_2薄膜相变温度调节问题的研究很有必要。详细介绍了元素掺杂、引入离子液体、氢化处理、界面应力调节等相变温度调节方法并阐述了其各自相变温度调节机理,同时比较了这几种方法的优缺点,并对未来研究方向作出展望,为今后VO2薄膜的制备与应用研究提供了重要参考。     

TiO2中间层对基于溶胶–凝胶法制备的VO2薄膜光学特性的影响（英文）

为了提高VO2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TiO2薄膜,再在光致亲水性处理的TiO2/云母基底上涂覆V2O5以及掺钨V2O5水溶胶,然后经热处理获得VO2/TiO2及VxW1-xO2/TiO2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,VO2/TiO2复合薄膜晶体生长为(011)面择优取向;VxW1-xO2/TiO2复合薄膜产生多种取向。TiO2中间层有助于使VO2薄膜生长致密,相变温度降低,更使VxW1-xO2/TiO2复合薄膜滞后温宽降至约4℃。     

The large modification of phase transition characteristics of VO2 films on SiO2/Si substrates

The vanadium oxide (VO₂) films have been prepared on SiO₂/Si substrates by using a modified Ion Beam Enhanced Deposition (IBED) method. During the film deposition, high doses of Ar⁺ and H⁺ ions have been implanted into the deposited films from the implanted beam. The resistance change of the VO₂ films with temperature has been measured and the phase transition process has been observed by using the X-ray Diffraction technique. The phase transition of the IBED VO₂ films starts at a low temperature of 48 °C and ends at a high temperature of 78 °C. It is found that the phase transition characteristics can be adjusted by changing the annealing temperature or the time and the phase transition characteristics of the IBED VO₂ films depend on the quantity and location of argon atoms in the film matrix.     

Lattice dynamics in VO2 near the metal-insulator transition

We present a comprehensive experimental study of the lattice dynamics in the vicinity of the metal-insulator transition in VO₂ by means of combined use of Raman spectroscopy and ultrasonic microscopy. Single crystalline samples of high quality particularly allow quite a complete determination of all Raman modes in the insulating phase at the Γ-point and the observation of an optical soft mode. In addition, the elastic behavior has been successfully investigated by measuring the propagation velocity of ultrasonic surface waves microscopically excited in various crystal directions. Our study reveals a striking coincidence of strong lattice softening attributable to certain acoustic branches and the occurrence of the optical soft mode, which precedes the metal-insulator transition over more than 100 K on approaching the critical temperature.     

Phase transition and switching in pyrolytic VO2 films

VO₂ films about 3000 Å thick have been prepared by the pyrolysis of vanadile acetylacetonate (C₅H₇O₂)₂ VO. The changes in the electrical, optical and structural properties of the films during the phase transition have been investigated. Various switching effects in VO₂ films have also been studied.     

IR spectra of VO2 and V2O3

IR spectra of the tetragonal modification of VO₂ and of the trigonal form of V₂O₃ are recorded at room temperature and compared with that of V₂O₅. The investigated samples of the two lower-valent vanadium oxides, obtained on temperature-programmed reduction treatment, were also characterized with diffuse reflectance and electron-paramagnetic resonance spectra. The effect of atmospheric oxygen on these materials was revealed with XPS measurements and also studied with IR spectra.     

Studies on the high-pressure reaction of Er2O3 and VO2

The reaction of erbium sesquioxide (Er₂O₃) and vanadium dioxide (VO₂) at 50 kbar and 30 kbar pressures and 1400°C were studied. In the course of the reaction, tetravalent vanadium ions were reduced to the trivalent state and erbium vanadites (ErVO₃) were obtained. The crystal structures of the products were examined by an x-ray diffraction analysis. At 50 kbar, a vaterite-type (μ-CaCO₃) compound isostructural with ErBO₃, which belonged to a hexagonal system, and at 30 kbar, a calcite-type vanadite belonging to a rhombohedral (pseudo-hexagonal) system were obtained. In the case of the reaction of erbium sesquioxide and vanadium trioxide (V₂O₃) at high pressure, a perovskite-type erbium vanadite was obtained. The magnetic properties of the compounds were studied.     

VO2(R) nanobelts resulting from the irreversible transformation of VO2(B) nanobelts

VO₂(R) nanobelts were prepared by the irreversible transformation of VO₂(B) nanobelts at the elevated temperature. The morphology and size of the VO₂(R) nanobelts were dependent on that of the precursor. VO₂(B) nanobelts were synthesized by a hydrothermal route, and the process of the VO₂(B) nanobelts' formation was also discussed. The product was characterized by a combination of techniques including XRD, TEM, FE-SEM, HRTEM, DTA and FT-IR. The as-obtained VO₂(R) nanobelts have a monoclinic structure with a length of 350-600 nm, a wideness of 100-150 nm and a thickness of 20-30 nm.     

High-pressure phase transition in Ho2O3

High-pressure X-ray diffraction and Raman studies on holmium sesquioxide (Ho₂O₃) have been carried out up to a pressure of ∼17 GPa in a diamond-anvil cell at room temperature. Holmium oxide, which has a cubic or bixbyite structure under ambient conditions, undergoes an irreversible structural phase transition at around 9.5 GPa. The high-pressure phase has been identified to be low symmetry monoclinic type. The two phases coexist to up to about 16 GPa, above which the parent phase disappears. The high-pressure laser-Raman studies have revealed that the prominent Raman band ∼370 cm⁻¹ disappears around the similar transition pressure. The bulk modulus of the parent phase is reported.     

Seebeck coefficient and electrical conductivity in the system TiO2VO2

The Seebeck coefficient and the electrical conductivity have been measured as functions of temperature in several compositions within the pseudobinary system TiO₂VO₂. It is found that the Seebeck coefficient is small and varying slowly with temperature while the dependence on temperature of the electrical conductivity is characterized by an activation energy with the value 0.24 eV.     

Crystal structure and phase transition of Rb2TeI6

At 293 K crystals of the title compound are tetragonal, space group P4/mnc, with $\text{a}\text{= 8.136(5)}\text{A}\text{?}$, $\text{c}\text{= 11.810(7)}\text{A}\text{?}$ and Z = 2. Octahedral TeI₆^2? anions (distance Te-I: 2.947(2)Å) show a 7.4° rotation around the fourfold axis against the cubic arrangement of the K₂PtCl₆ type structure. Beyond 340 K this cubic structure is found (space group Fm3m with a = 11.67(2) at 370 K).