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化学学报
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化学学报 ›› 2005, Vol. 63 ›› Issue (1): 81-85. 上一篇    下一篇

研究论文

Li＋-CaxPb1－xTiO3湿敏纳米薄膜的激光拉曼光谱、晶格畸变和激光显微组织——应用“软模理论”解谱

王智民*，李丽，刘静波，张艳熹   

  1. (黑龙江大学化学化工与材料学院 哈尔滨 150080)
  • 投稿日期:2003-12-12 修回日期:2004-09-13 发布日期:2010-12-10
  • 通讯作者: 王智民

LRS, Lattice Distortion and Polycrystal Microstructure of Li＋-CaxPb1－xTiO3 Nano-film Used for Humidity Sensor—Application of Soft Mode Theory

WANG Zhi-Min*, LI Li, LIU Jing-Bo, ZHANG Yan-Xi   

  1. (School of Chemistry and Materials Science, Heilongjiang University, Haerbin 150080)
  • Received:2003-12-12 Revised:2004-09-13 Published:2010-12-10
  • Contact: WANG Zhi-Min

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测定了标题物Li＋-CaxPb1－xTiO3 (缩写为Li-CPT, 其中x＝0.35, Li/Ti＝1.0%, mol/mol, 850 ℃/h)的激光拉曼光谱(LRS)和激光显微组织, 并与湿敏性能极差的纯钛酸铅PbTiO3 (缩写为PT)以及不同钙掺杂量的钛酸铅CaxPb1－xTiO3 (缩写为CPT, x＝0.08, 0.16, 0.24, 0.32, 0.40)的LRS进行比较, Li-CPT以及CPT的LRS与PT的LRS相比有很大差别,仅在75, 125, 190, 273和585 cm－1出现五个谱峰. 应用“软模理论”将其分别归属于PT四方晶相的五个特征单模E(1TO), A1(1TO), E(2TO), B1＋E和A1(3TO)的红移及宽化, PT的其它五个特征单模在Li-CPT及CPT的谱图中完全消失或被淹没. 对于这种拉曼活性的降低, 可以根据“软模理论”与晶格畸变作用的关联加以解释. Pauling离子半径较小的Ca2＋的掺杂, 等价取代了半径较大的Pb2＋的晶格位置, 降低了四方晶相畸变度δ＝c/a和不对称性导致的各向异性, 不单消除了薄膜冷却时位移型相变可能引起的破裂, 而且改变了晶格中氧八面体“TiO6”及十二面体“PbO12”的几何结构和电荷分布, 改变了晶格c轴上M-O (M＝Ti, Pb)键的化学环境, 直接阻尼了M—O键的伸缩振动软模, 减小了电偶矩及其自发极化, 使Li-CPT的振动模的拉曼活性大大降低, 因此LRS提供了一种表征晶格畸变的有效方法, 反过来也佐证了“软模理论”可以用来解释拉曼光谱.

关键词: 锂修饰钙掺杂钛酸铅(Li＋-CaxPb1－xTiO3, Li-CPT)的电阻-湿敏纳米薄膜, 激光拉曼光谱(LRS), 激光显微组织, 晶格畸变, 软模理论

Li＋-modified and Ca2＋-doped PbTiO3 humidity-sensitive nano-film (Li＋-CaxPb1－xTiO3, x＝0.35, Li/Ti＝1.0%, mol/mol, 850 ℃/h, abbreviated as Li-CPT) was prepared by the sol-spin-coating route using Ca(OAc)2, Pb(OAc)2, Li2CO3 and Ti(O-Bu-n)4 as starting materials. Li-CPT was studied by means of Laser Raman Spectroscopy (LRS) to characterize lattice distortion and polycrystal microstructure. In comparison with LRS of pure PbTiO3 (abbreviated as PT), those of both Li-CPT and CaxPb1－xTiO3 (abbreviated as CPT, x＝0.08, 0.16, 0.24, 0.32, 0.40) consist of only five peaks appearing at 75, 125, 190, 273 and 585 cm－1, while that of PT consists of ten peaks, namely E(1TO): 84, E(1LO): 105, A1(1TO): 145, E(2TO): 203, B1＋E: 289, A1(2TO): 332, E(2LO): 447, E(3TO): 500, A1(3TO): 597 and A1(3LO): 757 cm－1. According to "Soft Mode Theory", the five peaks of both Li-CPT and CPT, were attributed respectively to the red shift and extension of E(1TO), A1(1TO), E(2TO), B1＋E and A1(3TO) vibration soft mode of PT. Other five peaks of PT, E(1LO): 105, A1(2TO): 332, E(2LO): 447, E(3TO): 500 and A1(3LO): 757 cm－1, all disappeared or drowned in LRS of both Li-CPT and CPT. These results indicate that the crystal geometry and electron structure have been changed greatly after the equal-valence substitution of Pb2＋by Ca2＋with smaller Pauling ion radius: the substitution not only decreases the lattice distortion c/a and non-symmetry to remove film crack, but also changes the chemistry situation of M-O bond (M＝Ti/Pb), then alters the electric dipole moment and its polar rate. As a result the Raman activity has to be decreased enormously. Thus, LRS may be an effective technique for characterization of lattice distortion, and the soft mode theory may be used to explain some LRS.

Key words: Li＋-modified and Ca2＋-doped PbTiO3 (Li＋-Cax, Laser Raman Spectroscopy, laser microstructure, lattice distortion, soft mode theory