Nasir N, Grytsiv A, Melnychenko-Koblyuk N, Rogl P, Bauer E, Lackner R, Royanian E, Giester G, Saccone A
Institute of Physical Chemistry, University of Vienna, A-1090 Wien, Austria.
J Phys Condens Matter. 2009 Sep 23;21(38):385404. doi: 10.1088/0953-8984/21/38/385404. Epub 2009 Aug 27.
Novel ternary type-I clathrate compounds Ba(8){Zn,Cd}(x)Si(46-x), x∼7 have been synthesized from the elements by melting and reacting in quartz ampoules. Structural investigations for both compounds, i.e. x-ray single-crystal data at 300, 200 and 100 K for Ba(8)Zn(7)Si(39) and Rietveld data for Ba(8)Cd(7)Si(39), confirm cubic primitive symmetry consistent with the space group type [Formula: see text] (a(Ba(8)Zn(7)Si(39)) = 1.043 72(1) nm; a(Ba(8)Cd(7)Si(39)) = 1.058 66(3) nm). Whereas for Ba(8)Zn(7)Si(39) site 16i is completely occupied by Si atoms, a random atom distribution with different Zn/Si ratio exists for the two sites, 6d (0.77Zn+0.23Si) and 24k (0.91Si+0.09Zn). No vacancies are encountered and all atom sites are fully occupied. This atom distribution is independent of temperature. Rietveld refinements for Ba(8)Cd(7)Si(39) show that the 6d site is fully occupied by Cd atoms, leaving only the 24k site for a random occupation (0.96Si+0.04Cd) consistent with the chemical formula Ba(8)Cd(7)Si(39). The temperature-dependent x-ray spectra for Ba(8)Zn(7)Si(39) define an Einstein mode, Θ(E,U33) = 80 K. Studies of transport properties show electrons as the majority charge carriers in the system. Although the Cd- and Zn-based samples are isoelectronic, a significantly different electronic transport points towards substantial differences in the electronic density of states in both cases.
新型三元 I 型包合物 Ba(8){Zn,Cd}(x)Si(46 - x)，x∼7 已通过在石英安瓿中熔融和反应由元素合成。对这两种化合物进行了结构研究，即对 Ba(8)Zn(7)Si(39)在 300、200 和 100 K 下的 X 射线单晶数据以及对 Ba(8)Cd(7)Si(39)的 Rietveld 数据，证实了与空间群类型[公式：见正文]一致的立方原始对称性（a(Ba(8)Zn(7)Si(39)) = 1.043 72(1) nm；a(Ba(8)Cd(7)Si(39)) = 1.058 66(3) nm）。对于 Ba(8)Zn(7)Si(39)，16i 位点完全被 Si 原子占据，而对于 6d（0.77Zn + 0.23Si）和 24k（0.91Si + 0.09Zn）这两个位点存在不同 Zn/Si 比的随机原子分布。未发现空位且所有原子位点均被完全占据。这种原子分布与温度无关。对 Ba(8)Cd(7)Si(39)的 Rietveld 精修表明，6d 位点完全被 Cd 原子占据，仅留下 24k 位点进行随机占据（0.96Si + 0.04Cd），这与化学式 Ba(8)Cd(7)Si(39)一致。Ba(8)Zn(7)Si(39)的温度相关 X 射线光谱确定了一个爱因斯坦模式，Θ(E,U33) = 80 K。输运性质研究表明电子是该体系中的主要电荷载流子。尽管基于 Cd 和 Zn 的样品是等电子的，但显著不同的电子输运表明两种情况下电子态密度存在实质性差异。
