Hexagonal Tungsten Oxide Based Electrochromic Devices: Spectroscopic Evidence for the Li Ion Occupancy of Four-Coordinated Square Windows
Hexagonal Tungsten Oxide Based Electrochromic Devices: Spectroscopic Evidence for the Li Ion Occupancy of Four-Coordinated Square Windows
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DOI：
10.1021/cm8034455
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发表时间：
2009-04-14
影响因子：
8.6
通讯作者：
Bruening, Ralf
中科院分区：
文献类型：
--
作者：
Balaji, Subramanian;Djaoued, Yahia;Bruening, Ralf
以有机改性硅烷为模板剂，以钨酸为模板，在400℃下制备了六方大孔WO_3(h-WO_3)薄膜。构建了基于大孔h-WO_3层的非对称电致变色器件。用X射线衍射仪和显微拉曼光谱研究了锂在器件h-WO_3层中的插层/脱层过程随外加电压的变化。在h-WO_3中，Li+可以嵌入三个可能的位置：三角空穴(TC)、六方窗(HW)和四配位正方形窗(Sw)。X射线衍射仪测量表明，晶格参数发生了系统的变化，这与嵌入到h-WO_3层中的Li的量有关。相应地，拉曼光谱表明，在1.0V时，Li+完全填充TC位，部分填充HW位。当电位>；=1.5V时，Li+被插入到Sw中，这从v(O-W-O)拉曼模的消失中得到了证明。光学测量和拉曼光谱的可逆特性表明，电致变色器件中的变色过程主要是由于Li+占据了h-WO_3的HW和SW位。作为外加电势的函数进行的光学测量显示了有色和漂白状态之间的良好对比度，并使基于大孔h-WO_3的器件适合于智能窗应用。
Macroporous hexagonal WO3 (h-WO3) films were obtained at 400 degrees C from a sol containing tungstic acid with organically modified silane as a template. Asymmetric electrochromic devices based on the macroporous h-WO3 layer were constructed. XRD and micro-Raman studies of the intercalation/deintercalation of lithium into the h-WO3 layer of the device as a function of the applied voltages were performed. In h-WO3, Li+ can be intercalated into three potential sites: trigonal cavity (TC), hexagonal window (HW), and four-coordinated square window (SW). XRD measurements show systematic changes in the lattice parameter, which was associated with the amount of Li intercalated into the h-WO3 layer. Correspondingly, Raman spectroscopy shows that at 1.0 V Li+ completely fill TC and partially fill HW sites. For potentials >= 1.5 V, Li+ are inserted into the SW, as evidenced from the vanishing of the v(O-W-O) Raman modes. The reversible characteristics of the device from optical measurements and Raman spectra demonstrated that the coloration process in the electrochromic device is mainly due to the Li+ that occupy HW and SW sites of the h-WO3. Optical measurements performed as a function of applied potentials, show excellent contrasts between colored and bleached states and qualifies the macroporous h-WO3-based device for smart window applications.