Shiratori Yosuke, Magrez Arnaud, Dornseiffer Jürgen, Haegel Franz-Hubert, Pithan Christian, Waser Rainer
Institut für Elektronische Materialien, Institut für Festkörperforschung (IFF), Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany.
J Phys Chem B. 2005 Nov 3;109(43):20122-30. doi: 10.1021/jp052974p.
NaNbO(3) powders with various particle sizes (ranging from 30 nm to several microns) and well-controlled stoichiometry were obtained through microemulsion-mediated synthesis. The effect of particle size on the phase transformation of the prepared NaNbO(3) powders was studied using X-ray powder diffraction, Raman spectroscopy, and nuclear site group analysis based on these spectroscopic data. Coarsened particles exhibit an orthorhombic Pbcm (D(2h)(11), no. 57) structure corresponding to the bulk structure, as observed for single crystals or powders prepared by conventional solid-state reaction. The crystal symmetry of submicron powders was refined with the space group Pmc2(1) (C(2v)(2), no. 26). The reduced perovskite cell volumes of these submicron powders were most expanded compared to all the other structures. Fine particles with a diameter of less than 70 nm as measured from SEM observations showed an orthorhombic Pmma (D(2h)(5), no. 51) crystal symmetry. The perovskite formula cell of this structure was pseudocubic and was the most compact one. A possible mechanism of the phase transformation is suggested.
通过微乳液介导的合成方法获得了具有各种粒径（范围从30纳米到几微米）且化学计量比控制良好的NaNbO(3)粉末。使用X射线粉末衍射、拉曼光谱以及基于这些光谱数据的核位点群分析，研究了粒径对所制备的NaNbO(3)粉末相变的影响。如通过常规固态反应制备的单晶或粉末所观察到的那样，粗化颗粒呈现出与块状结构相对应的正交Pbcm（D(2h)(11)，编号57）结构。亚微米粉末的晶体对称性用空间群Pmc2(1)（C(2v)(2)，编号26）进行了细化。与所有其他结构相比，这些亚微米粉末的钙钛矿晶胞体积减小后扩张得最为明显。从扫描电子显微镜观察测量，直径小于70纳米的细颗粒呈现出正交Pmma（D(2h)(5)，编号51）晶体对称性。该结构的钙钛矿分子式晶胞为假立方结构，并且是最紧凑的一种。提出了相变的一种可能机制。
