Phase Width and Site Preferences in the EuMgxGa4−x Series
Phase Width and Site Preferences in the EuMgxGa4−x Series
复制标题
EuMgxGa4−x 系列中的相宽和位点偏好
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
G. Miller
中科院分区：
文献类型：
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作者：
T. You;G. Miller
采用高温固相法合成了一系列EuMgxGa 4 −x化合物，并通过粉末和单晶X射线衍射进行了表征。所有化合物均为四方BaAl 4型结构（空间群I4/mmm，Z = 2，Pearson符号tI 10），Ga完全占据顶端原子（4 e）位，Mg和Ga混合占据基底原子（4d）位。通过单晶X射线衍射分析了六种组成：EuMg0.21（1）Ga3.79（1）、EuMg0.91（1）Ga3.09（1）、EuMg1.22（1）Ga2.78（1）、EuMg1.78（1）Ga2.22（1）、EuMg1.84（1）Ga2.16（1）和EuMg1.94（1）Ga2.06（1）。随着较大的Mg原子越来越多地取代EuMgxGa 4-x中基位的Ga原子，a轴长度首先减小，然后增加，而c轴长度则沿着系列单调增加。BaAl 4型EuMgxGa 4 −x系列的相宽度被确定为0 ≤ x ≤ 1.94（1），对应于每个分子式单元12.06（1）-14个价电子的范围，并且可以通过使用通过紧束缚计算计算的态密度（DOS）曲线的电子结构来理解。Mg取代Ga的基础网站是一致的网站偏好的BaAl 4-结构的三维框架上的混合金属的电负性和大小的基础上，并提供了在晶格参数的不寻常的行为的理由。所观察到的网站偏好也合理化的总电子能量计算两种不同的着色方案。
A series of EuMgxGa4−x compounds were synthesized using high temperature, solid-state methods and characterized by both powder and single crystal X-ray diffraction. All compounds crystallize in the tetragonal BaAl4-type structure (space group I4/mmm, Z = 2, Pearson symbol tI10) with full occupancy of Ga at the apical atom (4e) site and mixed-occupancy of Mg and Ga at the basal atom (4d) site. Six compositions were analyzed by single crystal X-ray diffraction: EuMg0.21(1)Ga3.79(1), EuMg0.91(1)Ga3.09(1), EuMg1.22(1)Ga2.78(1), EuMg1.78(1)Ga2.22(1), EuMg1.84(1)Ga2.16(1), and EuMg1.94(1)Ga2.06(1). As the larger Mg atoms increasingly replace Ga atoms at the basal site in EuMgxGa4−x, the a-axis lengths at first decrease and then increase, while the c-axis lengths increase monotonically along the series. The phase width of the BaAl4-type EuMgxGa4−x series is identified to be 0 ≤ x ≤ 1.94(1), a range which corresponds to 12.06(1)-14 valence electrons per formula unit, and can be understood by their electronic structures using density of states (DOS) curves calculated by tight-binding calculations. Mg substitution for Ga at the basal site is consistent with the site preferences for mixed metals on the three-dimensional framework of the BaAl4-structure based on both electronegativities and sizes, and provides the rationale for the unusual behavior in lattice parameters. The observed site preference was also rationalized by total electronic energies calculated for two different coloring schemes.