Gd12Co5.3Bi and Gd12Co5Bi, Crystalline Doppelgänger with Low Thermal Conductivities

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• 作者：Anton O. Oliynyk ; Taylor D. Sparks ; Michael W. Gaultois ; Leila Ghadbeigi ; Arthur Mar
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：July 5, 2016
• 年：2016
• 卷：55
• 期：13
• 页码：6625-6633
• 全文大小：537K
• 年卷期：0
• ISSN：1520-510X

文摘

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 Gd₁₂Co_5.3Bi 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 Gd₁₂Co_5.3Bi and Gd₁₂Co₅Bi are distinct phases. The higher symmetry structure of Gd₁₂Co_5.3Bi (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 Gd₁₂Co_5.3Bi, but they are ordered in Gd₁₂Co₅Bi. Consistent with this disorder, the electrical resistivity shows less dependence on temperature for Gd₁₂Co_5.3Bi 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 Gd₁₂Co_5.3Bi 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.