Effect of Isovalent Substitution on the Structure and Properties of the Zintl Phase Solid Solution Eu7Cd4Sb8-xAsx (2 ≤ x ≤ 5).
Effect of Isovalent Substitution on the Structure and Properties of the Zintl Phase Solid Solution Eu7Cd4Sb8-xAsx (2 ≤ x ≤ 5).
复制标题
DOI：
10.1021/acs.inorgchem.5b01909
复制
发表时间：
2015-11
影响因子：
4.6
通讯作者：
Joya A. Cooley;Nasrin Kazem;J. Zaikina;J. Fettinger;S. Kauzlarich
中科院分区：
文献类型：
--
作者：
Joya A. Cooley;Nasrin Kazem;J. Zaikina;J. Fettinger;S. Kauzlarich
采用熔锡助熔剂法合成了一种新型Zintl相结构类型Eu 7 Cd 4Sb 8-xAsx（x = 2，3，4，5），通式为Eu 7 Cd 4Pn 8（Pn = Sb和As混合占位）。用单晶X射线衍射法测定了其结构。在我们的实验条件下，这种结构类型仅在2 ≤ x ≤ 5时保持不变，并且合成具有x 5的样品的努力导致了其他结构类型。混合占据的Sb和As可以被认为是一个假原子，其理想的尺寸，在这个范围内的Sb/As的比例，适合的结构。标题相的晶体结构为I心单斜晶系，空间群为I2/m（No.12，Z = 4），晶胞参数范围如下：a = 19.7116（17）-19.4546（13）<$，B = 4.6751（4）-4.6149（3）<$，c = 24.157（2）-23.871（15）<$，β = 95.8798（1）-96.016（5）°，取决于Sb/As比。该结构可以描述为由Cd-Pn和Pn-Pn键合形成的平行双五边形管。这些双五边形是通过Cd为中心的CdPn 4四面体的角共享和两个相邻CdPn 4四面体的Pn-Pn相互作用形成的。这种结构类型与Sr 11 Cd 6Sb 12结构类型密切相关，因为两者具有相同的Pn-Pn键和双五边形管的键合特征。电子探针分析证实了这些新的Zintl固溶体相的组成。的作为表现出优先取代特定的网站，和网站特异性的趋势支持最低能量模型从理论计算。理论计算还预测，富锑化合物应该是金属或半金属，它们应该成为更多的绝缘作为内容的增加。在50 ~ 300 K之间，固溶体的电阻率相对较低，范围为0.57 ~ 0.26 mΩ·cm，随As含量的增加而增加。
A novel Zintl phase structure type, Eu7Cd4Sb8-xAsx (x = 2, 3, 4, and 5), with the general formula Eu7Cd4Pn8 (Pn = mixed occupancy Sb and As), was synthesized by molten tin flux reaction. Its structure was determined using single-crystal X-ray diffraction methods. This structure type is only preserved for 2 ≤ x ≤ 5 under our experimental conditions, and efforts to synthesize samples with x 5 resulted in other structure types. The mixed occupancy Sb and As can be thought of as a pseudoatom whose ideal size, in this range of Sb/As ratios, fits the structure. The title phase crystallizes in the I-centered monoclinic space group I2/m (No. 12, Z = 4) with unit cell parameters ranging as follows: a = 19.7116(17)-19.4546(13) Å, b = 4.6751(4)-4.6149(3) Å, c = 24.157(2)-23.871(15) Å, and β = 95.8798(1)-96.016(5)°, depending on the Sb/As ratio. The structure can be described as parallel double pentagonal tubes resulting from Cd-Pn and Pn-Pn bonding. These double pentagons are formed through corner sharing of the Cd-centered CdPn4 tetrahedra and a Pn-Pn interaction from two adjacent CdPn4 tetrahedra. This structure type is closely related to the Sr11Cd6Sb12 structure type as both share the same bonding features of Pn-Pn bonding and double pentagonal tubes. Electron microprobe analysis confirms the composition of these new Zintl solid solution phases. The As exhibits preferential substitution on specific sites, and site specificity trends are supported by lowest energy models from theoretical calculations. Theoretical calculations also predict that Sb-rich compounds should be metallic or semimetallic and that they should become more insulating as As content increases. Members of the solid-solution order ferromagnetically between 5 and 6 K and exhibit relatively low electrical resistivity between 50 and 300 K, ranging from ∼0.57 to ∼26 mΩ·cm, increasing with increasing As content.