Poddig Hagen, Finzel Kati, Doert Thomas
Inorganic Chemistry, Technische Universität Dresden, Bergstrasse 66, Dresden 01069, Germany.
Theoretical Chemistry, Technische Universität Dresden, Bergstrasse 66c, Dresden 01069, Germany.
Acta Crystallogr C Struct Chem. 2020 Jun 1;76(Pt 6):530-540. doi: 10.1107/S2053229620005094. Epub 2020 May 6.
Crystals of the rare earth metal polytelluride LaTe, namely, lanthanum telluride (1/1.8), have been grown by molten alkali halide flux reactions and vapour-assisted crystallization with iodine. The two-dimensionally incommensurately modulated crystal structure has been investigated by X-ray diffraction experiments. In contrast to the tetragonal average structure with unit-cell dimensions of a = 4.4996 (5) and c = 9.179 (1) Å at 296 (1) K, which was solved and refined in the space group P4/nmm (No. 129), the satellite reflections are not compatible with a tetragonal symmetry but enforce a symmetry reduction. Possible space groups have been derived by group-subgroup relationships and by consideration of previous reports on similar rare earth metal polychalcogenide structures. Two structural models in the orthorhombic superspace group, i.e. Pmmn(α,β,1/2)000(-α,β,1/2)000 (No. 59.2.51.39) and Pm2n(α,β,1/2)000(-α,β,1/2)000 (No. 31.2.51.35), with modulation wave vectors q = αa* + βb* + 1/2c* and q = -αa* + βb* + 1/2c* [α = 0.272 (1) and β = 0.314 (1)], have been established and evaluated against each other. The modulation describes the distribution of defects in the planar [Te] layer, coupled to a displacive modulation due to the formation of different Te anions. The bonding situation in the planar [Te] layer and the different Te anion species have been investigated by density functional theory (DFT) methods and an electron localizability indicator (ELI-D)-based bonding analysis on three different approximants. The temperature-dependent electrical resistance revealed a semiconducting behaviour with an estimated band gap of 0.17 eV.
稀土金属多碲化物LaTe，即碲化镧(1/1.8)的晶体，已通过熔融碱金属卤化物助熔剂反应和碘辅助气相结晶法生长出来。通过X射线衍射实验对其二维非公度调制晶体结构进行了研究。在296(1)K时，其四方平均结构的晶胞参数为a = 4.4996(5) Å和c = 9.179(1) Å，该结构在空间群P4/nmm（编号129）中解析并精修，但卫星反射与四方对称性不兼容，而是导致对称性降低。通过群子群关系并参考先前关于类似稀土金属多硫族化物结构的报道，推导了可能的空间群。在正交超空间群中有两个结构模型，即Pmmn(α,β,1/2)000(-α,β,1/2)000（编号59.2.51.39）和Pm2n(α,β,1/2)000(-α,β,1/2)000（编号31.2.51.35），其调制波矢q = αa* + βb* + 1/2c和q = -αa + βb* + 1/2c* [α = 0.272(1)，β = 0.314(1)]，已建立并相互评估。该调制描述了平面[Te]层中缺陷的分布，这与由于不同Te阴离子的形成而产生的位移调制相关。通过密度泛函理论(DFT)方法以及基于电子定域性指标(ELI-D)的键合分析，研究了平面[Te]层中的键合情况以及三种不同近似结构中不同的Te阴离子种类。与温度相关的电阻显示出半导体行为，估计带隙为0.17 eV。
