Oliynyk Anton O, Sparks Taylor D, Gaultois Michael W, Ghadbeigi Leila, Mar Arthur
Department of Chemistry, University of Alberta , Edmonton, AB T6G 2G2, Canada.
Department of Materials Science and Engineering, University of Utah , Salt Lake City, Utah 84112, United States.
Inorg Chem. 2016 Jul 5;55(13):6625-33. doi: 10.1021/acs.inorgchem.6b00826. Epub 2016 Jun 14.
Attempts to prepare Gd12Co5Bi, a member of the rare-earth (RE) intermetallics RE12Co5Bi, which were identified by a machine-learning recommendation engine as potential candidates for thermoelectric materials, led instead to formation of the new compound Gd12Co5.3Bi with a very similar composition. Phase equilibria near the Gd-rich corner of the Gd-Co-Bi phase diagram were elucidated by both lab-based and variable-temperature synchrotron powder X-ray diffraction, suggesting that Gd12Co5.3Bi and Gd12Co5Bi are distinct phases. The higher symmetry structure of Gd12Co5.3Bi (cubic, space group Im3̅, Z = 2, a = 9.713(6) Å), as determined from single-crystal X-ray diffraction, is closely related to that of Gd12Co5Bi (tetragonal, space group Immm). Single Co atoms and Co-Co dumbbells are disordered with occupancies of 0.78(2) and 0.22(2), respectively, in Gd12Co5.3Bi, but they are ordered in Gd12Co5Bi. Consistent with this disorder, the electrical resistivity shows less dependence on temperature for Gd12Co5.3Bi than for Gd12Co5Bi. The thermal conductivity is low and reaches 2.8 W m(-1) K(-1) at 600 °C for both compounds; however, the temperature dependence of the thermal conductivity differs, decreasing for Gd12Co5.3Bi and increasing for Gd12Co5Bi as the temperature increases. The unusual trends in thermal properties persist in the heat capacity, which decreases below 2R, and in the thermal diffusivity, which increases at higher temperatures.
通过机器学习推荐引擎识别为热电材料潜在候选物的稀土（RE）金属间化合物RE12Co5Bi的成员Gd12Co5Bi的制备尝试，反而导致形成了具有非常相似组成的新化合物Gd12Co5.3Bi。从基于实验室的和可变温度的同步加速器粉末X射线衍射阐明了Gd-Co-Bi相图富Gd角附近的相平衡，表明Gd12Co5.3Bi和Gd12Co5Bi是不同的相。由单晶X射线衍射确定，Gd12Co5.3Bi（立方，空间群Im3̅，Z = 2，a = 9.713(6) Å）的较高对称性结构与Gd12Co5Bi（四方，空间群Immm）密切相关。在Gd12Co5.3Bi中，单个Co原子和Co-Co哑铃状原子无序，占有率分别为0.78(2)和0.22(2)，但在Gd12Co5Bi中它们是有序的。与这种无序一致，Gd12Co5.3Bi的电阻率对温度的依赖性比对Gd12Co5Bi的小。两种化合物的热导率都很低，在600℃时达到2.8 W m(-1) K(-1)；然而，热导率的温度依赖性不同，随着温度升高，Gd12Co5.3Bi的热导率降低，Gd12Co5Bi的热导率增加。热性质的异常趋势在低于2R时降低的热容以及在较高温度下增加的热扩散率中持续存在。
