EuGa2.+‐.xGe4.+‐.x: Preparation, Crystal Chemistry and Properties.
EuGa2.+‐.xGe4.+‐.x: Preparation, Crystal Chemistry and Properties.
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EuGa2.+‐.xGe4.+‐.x：制备、晶体化学和性质。
DOI：
10.1002/chin.200233004
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发表时间：
2002
期刊：
影响因子：
--
通讯作者：
Y. Grin
中科院分区：
文献类型：
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作者：
W. Carrillo‐Cabrera;S. Paschen;Y. Grin
标题化合物是由这些元素的混合物在玻璃碳坩埚(HF炉，Ar气氛)中熔化而成的。EuGa2±xGe4∓x以一种新的结构类型(正交对称，空间群CMCM(NO.63)，a=4.1571(3)？，b=11.268(1)？，c=13.155(1)？，V=13.155(2)？3，Z=4，皮尔逊符号oC28)结晶，其特征是具有4重键合的(4b)E原子(E=Ga，Ge)的三维骨架，通道平行于短a轴。Eu原子位于这些通道的E18空穴中。该结构还可以被描述为来自BaAl2Si2的片段和来自重建的钻石类型结构的片段的共生。标题化合物的(Ga，Ge)24骨架相当于CsAlSi5O12沸石结构中的Si(Al)原子的骨架。磁化率测量表明，在约9K时，EuGa2±xGe4∓x经历了从顺磁到反铁磁有序态的转变。在顺磁区，得到了2+对Eu的氧化态(μEff≈8μB/Eu)。EuGa2Ge4的晶体化学式为Eu2+[(4b)Ga1−]2[(4b)Ge0]4。量子化学计算(Tb-LMTO，ELF)证实了这一点。然而，与其他几种类似的化合物一样，如碱土金属笼合物，EuGa2±xGe4∓x具有与金属相似的温度依赖关系，具有较低的载流子浓度，与计算态密度的低值一致。
The title compound was prepared from a mixture of the elements by melting in a glassy carbon crucible (HF furnace, argon atmosphere). EuGa2±xGe4∓xcrystallizes in a new structure type (orthorhombic symmetry, space group Cmcm (no. 63), a=4.1571(3) Å, b=11.268(1) Å, c=13.155(1) Å, V=616.2(2) Å3, Z=4, Pearson symbol oC28) and is characterized by a 3D framework of 4-fold bonded (4b) E atoms (E=Ga,Ge) with channels parallel to the short a-axis. The europium atoms lie in the E18holes of those channels. The structure can also be described as an intergrowth of segments from BaAl2Si2and from a reconstructed diamond type of structure. The (Ga,Ge)24framework of the title compound is equivalent to that of the Si(Al) atoms in the zeolite structure of CsAlSi5O12. Magnetic susceptibility measurements show that EuGa2±xGe4∓xundergoes a transition from a paramagnetic to an antiferromagnetic ordered state at about 9 K. In the paramagnetic region, an oxidation state of 2+ for europium (μeff≈8 μB/Eu) was obtained. The crystal chemical formula of EuGa2Ge4is Eu2+[(4b)Ga1−]2[(4b)Ge0]4according to a charge balanced Zintl phase. This was confirmed by quantum chemical calculations (TB-LMTO, ELF). However, like several other similar compounds, e.g. alkaline earth metal clathrates, EuGa2±xGe4∓xhas a metal-like temperature dependence of the electrical resistivity with a low charge-carrier concentration in agreement with the low value of the calculated density of states.