Failamani F, Grytsiv A, Giester G, Polt G, Heinrich P, Michor H, Bauer E, Zehetbauer M, Rogl P
Institute of Materials Chemistry and Research, Faculty of Chemistry, University of Vienna, Währingerstraße 42, A-1090 Vienna, Austria.
Phys Chem Chem Phys. 2015 Oct 7;17(37):24248-61. doi: 10.1039/c5cp04000k. Epub 2015 Sep 1.
The novel compounds Ba5{V,Nb}12Sb19+x, initially found in diffusion zone experiments between Ba-filled skutterudite Ba0.3Co4Sb12 and group V transition metals (V,Nb,Ta), were synthesized via solid state reaction and were characterized by means of X-ray (single crystal and powder) diffraction, electron probe microanalysis (EPMA), and physical (transport and mechanical) properties measurements. Ba5V12Sb19.41 (a = 1.21230(1) nm, space group P4[combining overline]3m; RF(2) = 0.0189) and Ba5Nb12Sb19.14 (a = 1.24979(2) nm, space group P4[combining overline]3m; RF(2) = 0.0219) are the first representatives of the Ba5Ti12Sb19+x-type, however, in contrast to the aristotype, the structure of Ba5V12Sb19.41 shows additional atom disorder. Temperature dependent ADPs and specific heat of Ba5V12Sb19.41 confirmed the rattling behaviour of Ba1,2 and Sb7 atoms within the framework built by V and Sb atoms. Electrical resistivity of both compounds show an upturn at low temperature, and a change from p- to n-type conductivity above 300 K in Ba4.9Nb12Sb19.4. As expected from the complex crystal structure and the presence of defects and disorder, the thermal conductivity is suppressed and lattice thermal conductivity of ∼0.43 W m(-1) K(-1) is near values typical for amorphous systems. Vicker's hardness of (3.8 ± 0.1) GPa (vanadium compound) and (3.5 ± 0.2) GPa (niobium compound) are comparable to Sb-based filled skutterudites. However, the Young's moduli measured by nanoindentation for these compounds EI(Ba4.9V12Sb19.0) = (85 ± 2) GPa and EI(Ba4.9Nb12Sb19.4) = (79 ± 5) GPa are significantly smaller than those of skutterudites, which range from about 130 to 145 GPa.
新型化合物Ba5{V,Nb}12Sb19+x最初是在充满Ba的方钴矿Ba0.3Co4Sb12与V族过渡金属（V、Nb、Ta）之间的扩散区实验中发现的，通过固态反应合成，并通过X射线（单晶和粉末）衍射、电子探针微分析（EPMA）以及物理（输运和力学）性能测量进行表征。Ba5V12Sb19.41（a = 1.21230(1) nm，空间群P4[上加横线]3m；RF(2) = 0.0189）和Ba5Nb12Sb19.14（a = 1.24979(2) nm，空间群P4[上加横线]3m；RF(2) = 0.0219）是Ba5Ti12Sb19+x型的首批代表物，然而，与原型相比，Ba5V12Sb19.41的结构显示出额外的原子无序。Ba5V12Sb19.41的温度依赖性非谐性位移参数和比热证实了Ba1,2和Sb7原子在由V和Sb原子构成的框架内的晃动行为。两种化合物的电阻率在低温下出现上升，并且在Ba4.9Nb12Sb19.4中300 K以上从p型导电转变为n型导电。正如从复杂晶体结构以及缺陷和无序的存在所预期的那样，热导率受到抑制，晶格热导率约为0.43 W m(-1) K(-1)，接近非晶体系的典型值。V族化合物的维氏硬度为(3.8 ± 0.1) GPa，铌化合物的维氏硬度为(3.5 ± 0.2) GPa，与Sb基填充方钴矿相当。然而，通过纳米压痕测量的这些化合物的杨氏模量EI(Ba4.9V12Sb19.0) = (85 ± 2) GPa和EI(Ba4.9Nb12Sb19.4) = (79 ± 5) GPa明显小于方钴矿的杨氏模量，方钴矿的杨氏模量范围约为130至145 GPa。
