STRUCTURE OF A POLYTYPE OF THE INORGANIC MISFIT-LAYER COMPOUND (PBS)1.18TIS2
STRUCTURE OF A POLYTYPE OF THE INORGANIC MISFIT-LAYER COMPOUND (PBS)1.18TIS2
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无机错配层化合物(PBS)1.18TIS2的多型体的结构
DOI：
10.1103/physrevb.46.2750
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发表时间：
1992
影响因子：
3.7
通讯作者：
J. Deboer
中科院分区：
文献类型：
--
作者：
S. Vansmaalen;J. Deboer
第二个修改报告的无机失配层化合物（PbS）1.18TiS2。它被发现是一个真正的多型以前分析的单斜晶型。在后者中的层的AB堆叠被替换为在该正交变型中的堆叠AB A 'B'。对（PbS）1.18TiS2的晶体进行单晶X射线衍射测量（Mo K-α辐射，λ =0.71073埃）。该结构由两个调制子系统（nu = 1，2）描述，它们具有共同的（a（nu-2）*，a（nu-3）*）倒易晶格面。超空间嵌入由四个倒易格向量得出，由a1*=a11*，a2*=a12*，a3*=a13* 和a4*=a21* 给出。其对称性由超空间群G（s）=P：Cmca（alpha-0，0，）1 ssBAR给出。第一子系统（TiS 2）的晶格参数为a11 = 3.409（1）埃，a12 = 5.882（1）埃，以及a13=23.409（3）埃，其中调制波矢量q1=a21*= α-oa 11 *，并且α-0 = 0.5875（3）。它的子空间群是P：Cmca（alpha-0，0，0）1 ssBAR。第二子系统（PbS）具有晶格参数a21=5.802（1）埃、a22=a12和a23=a13，调制波矢量q2=a11*。子系统的超空间群是P：Cmna（alpha-0（-1，0，0）11 sBAR。对1123个主反射和186个I > 2.5-sigma（I）的一阶卫星进行细化，平滑地收敛到R（F）2=0.163（R（F）=0.111）。最终的结构模型包括位移调制参数的二次谐波铅，和其他原子的一次谐波。最大的调制幅度上发现的PbS子系统的两个原子。它们主要描述平行于层的位移，沿着相称方向a（nu-2）。结果表明，单斜晶系和斜方晶系的局域结构非常相似。
A second modification is reported of the inorganic misfit-layer compound (PbS)1.18TiS2. It is found to be a true polytype of the previously analyzed monoclinic form. The AB stacking of layers in the latter is replaced by a stacking AB A'B' in this orthorhombic modification. Single-crystal x-ray diffraction measurements (Mo K-alpha radiation, lambda=0.71073 angstrom) were performed on a crystal of (PbS)1.18TiS2. The structure is described by two modulated subsystems (nu = 1,2), which have the (a(nu-2)*,a(nu-3)*) reciprocal-lattice plane in common. A superspace embedding follows from four reciprocal-lattice vectors, given by a1*=a11*, a2*=a12*, a3*=a13*, and a4*=a21*. The symmetry is given by the super space group G(s)=P:Cmca(alpha-0,0,)1ssBAR. Lattice parameters for the first subsystem (TiS2) are a11 = 3.409(1) angstrom, a12 = 5.882(1) angstrom, and a13=23.409(3) angstrom, with modulation wave vector q1=a21*=alpha-oa11*, and alpha-0 = 0.5875(3). Its subsystem superspace group is P:Cmca(alpha-0,0,0)1ssBAR. The second subsystem (PbS) has lattice parameters a21=5.802(1) angstrom, a22=a12, and a23=a13, with modulation wave vector q2=a11*. The subsystem superspace group is P:Cmna(alpha-0(-1),0,0)11sBAR. Refinements on 1123 main reflections and 186 first-order satellites with I > 2.5-sigma(I), converged smoothly to R(F)2=0.163(R(F)=0.111). The final structure model included displacive modulation parameters up to second harmonics for Pb, and first harmonics for the other atoms. The largest modulation amplitudes are found on both atoms of the PbS subsystem. They mainly describe displacements parallel to the layers, along the commensurate direction a(nu-2). It is shown that the local structures in the monoclinic and the orthorhombic forms are very much alike.