Gomez-Herrero A, Otero-Diaz LC
Dpto. Inorganica, Fac. C.C. Quimicas, Universidad Complutense, Madrid, Spain.
Micron. 2000 Oct;31(5):597-603. doi: 10.1016/s0968-4328(99)00142-0.
Two new misfit layer structures have been synthesized within the Sb-Nb-Se system. Powder X-ray diffraction and electron microscopy techniques (electron diffraction, HREM, XEDS) have been used to determine the nature of their structure. According to TEM and XEDS data (for more than 15 crystals studied) both phases are monolayer type, i.e. (SbSe)1+delta (NbSe2). Electron microscopy reveals a composite modulated structure that consists of the periodical intergrowth of a pseudotetragonal SbSe layer, denominated as Q, and a pseudohexagonal layer NbSe2, denominated as H. Both layers fit along b, stack along c and do not fit along a (misfit) giving rise to an incommensurate modulation along this direction. The two phases differ in the symmetry of the Q layers being in one case orthorhombic (for delta = 0.17) and monoclinic in the other (for delta = 0.19). After the characterization of the sample by electron microscopy the unit cells of the basic layers could be refined for both phases by powder X-ray diffraction: aQ = 5.824(2) A, bQ = 5.962(5) A, cQ = 23.927(6) A, alpha = 90 degrees, beta = 90 degrees and gamma = 90 degrees and aH = 3.415(5) A, bH = 5.962(6) A,, cH = 11.962(1) A, alpha = 90 degrees, beta = 90 degrees and gamma = 90 degrees for the orthorhombic phase; aQ = 5.844(2) A, bQ = 5.981(1) A, cQ = 23.919(5) A, alpha = 90 degrees, beta = 90 degrees and gamma = 96.00(3)degrees and aH = 3.439(1) A, bH = 5.994(2) A, cH = 11.956(3) A, alpha = 90 degrees, beta = 90 degrees and gamma = 90 degrees for the monoclinic phase. The phase with the monoclinic Q-sublattice often appears as twinned crystals. The more abundant crystals are disordered intergrowths of both monolayer phases.
在Sb-Nb-Se体系中合成了两种新的失配层结构。利用粉末X射线衍射和电子显微镜技术（电子衍射、高分辨电子显微镜、能量过滤X射线能谱）确定了它们的结构性质。根据透射电子显微镜和能量过滤X射线能谱数据（对超过15个研究晶体），两个相均为单层型，即(SbSe)1+δ(NbSe2)。电子显微镜揭示了一种复合调制结构，它由被称为Q的假四方SbSe层和被称为H的假六方NbSe2层的周期性共生组成。两层沿b方向匹配，沿c方向堆叠，沿a方向不匹配（失配），从而在该方向上产生非相称调制。这两个相在Q层的对称性上有所不同，一种情况是正交晶系（δ = 0.17），另一种是单斜晶系（δ = 0.19）。通过电子显微镜对样品进行表征后，可通过粉末X射线衍射对两个相的基本层的晶胞进行精修：正交晶系相的aQ = 5.824(2) Å，bQ = 5.962(5) Å，cQ = 23.927(6) Å，α = 90°，β = 90°，γ = 90°，aH = 3.415(5) Å，bH = 5.962(6) Å，cH = 11.962(1) Å，α = 90°，β = 90°，γ = 90°；单斜晶系相的aQ = 5.844(2) Å，bQ = 5.981(1) Å，cQ = 23.919(5) Å，α = 90°，β = 90°，γ = 96.00(3)°，aH = 3.439(1) Å，bH = 5.994(2) Å，cH = 11.956(3) Å，α = 90°，β = 90°，γ = 90°。具有单斜Q亚晶格的相经常以孪晶形式出现。数量较多的晶体是两个单层相的无序共生体。
