Xu Gang, Zhang Ya-Wen, Sun Xiao, Xu Chang-Liang, Yan Chun-Hua
State Key Laboratory of Rare Earth Materials Chemistry and Applications, PKU-HKU Joint Laboratory on Rare Earth Materials and Bioinorganic Chemistry, Peking University, Beijing 100871, China.
J Phys Chem B. 2005 Mar 3;109(8):3269-78. doi: 10.1021/jp045282u.
Weakly agglomerated nanocrystalline scandia doped tin oxide powders with high surface area (170-220 m(2)/g) and uniform size (3-4 nm) were synthesized for the first time by a two-step hydrothermal process in the presence of urea, followed by the calcination between 500 and 1200 degrees C. The structure and texture of the binary oxide system were characterized by thermogravimetry and differential thermal analysis, Brunauer-Emmett-Teller-specific surface area analysis, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. A metastable scandium tin oxide solid solution in tetragonal structure was formed for the scandia content lower than 6 mol % as the samples were calcined at 800 degrees C, and the excess Sc atoms were dispersed at the surface of the crystallites above this limit. The solid solution was metastable, so scandium migrated toward the surface region of the crystallites and produced a second phase of Sc(4)Sn(3)O(12) during calcining at high temperatures over 1000-1200 degrees C. In the case of the samples with higher dopant concentration (>15 mol %), the calcination at the temperature between 500 and 800 degrees C caused the precipitation of Sc(2)O(3), and the calcination over 1000-1200 degrees C led to the formation of more Sc(4)Sn(3)O(12). Textural analysis showed that doping an appropriate amount of Sc(2)O(3) into nanosized SnO(2) could effectively inhibit the grain growth and stabilize the surface area against high-temperature calcinations below 1000 degrees C. CO gas-sensing property measurements revealed that the dispersion of Sc at the surfaces of the SnO(2) nanocrystallites could improve the CO sensitivity significantly, and the pellet sample with scandia content of 10 mol % sintered at 800 degrees C showed the best CO gas-sensing property in the operation temperature range of 300-400 degrees C. On the basis of the structural and textural analysis, the correlation between the structure/texture and the sensitivity to CO for the as-calcined (SnO(2))(1-x)(Sc(2)O(3))(x) nanocrystallites has been established and explained.
首次通过两步水热法在尿素存在下合成了具有高比表面积（170 - 220 m²/g）和均匀尺寸（3 - 4 nm）的弱团聚纳米晶钪掺杂氧化锡粉末，随后在500至1200℃之间进行煅烧。通过热重分析和差示热分析、布鲁诺尔 - 埃米特 - 泰勒比表面积分析、透射电子显微镜、X射线衍射、拉曼光谱和X射线光电子能谱对二元氧化物体系的结构和织构进行了表征。当样品在800℃煅烧时，钪含量低于6 mol%会形成四方结构的亚稳钪锡氧化物固溶体，超过此限度多余的Sc原子会分散在微晶表面。该固溶体是亚稳的，因此在1000 - 1200℃以上的高温煅烧过程中，钪会向微晶表面区域迁移并生成Sc₄Sn₃O₁₂第二相。对于掺杂浓度较高（>15 mol%）的样品，在500至800℃之间煅烧会导致Sc₂O₃沉淀，在1000 - 1200℃以上煅烧会导致更多Sc₄Sn₃O₁₂形成。织构分析表明，向纳米级SnO₂中掺杂适量的Sc₂O₃可以有效抑制晶粒生长，并在低于1000℃的高温煅烧下稳定比表面积。CO气敏性能测量表明，Sc在SnO₂纳米微晶表面的分散可以显著提高CO灵敏度，钪含量为10 mol%且在800℃烧结的颗粒样品在300 - 400℃的操作温度范围内表现出最佳的CO气敏性能。基于结构和织构分析，建立并解释了煅烧后的(SnO₂)₁₋ₓ(Sc₂O₃)ₓ纳米微晶的结构/织构与对CO的灵敏度之间的相关性。
