Gd₁₂Co_5.3Bi and Gd₁₂Co₅Bi, Crystalline Doppelgänger with Low Thermal Conductivities

Journal Article · Tue Jun 14 00:00:00 EDT 2016 · Inorganic Chemistry

DOI:https://doi.org/10.1021/acs.inorgchem.6b00826· OSTI ID:1322339

Oliynyk, Anton O. ^[1]; Sparks, Taylor D. ^[2]; Gaultois, Michael W. ^[3]; Ghadbeigi, Leila ^[2]; Mar, Arthur ^[1]

---

1. Univ. of Alberta, Edmonton, AB (Canada)
2. Univ. of Utah, Salt Lake City, UT (United States)
3. Univ. of Cambridge (United Kingdom)

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 Gd12Co5.3Bi (cubic, space group $$Im\bar{3}$$, 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. Here, 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.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES); Marie Skłodowska-Curie
• Grant/Contract Number: AC02-06CH11357; 659764
• OSTI ID: 1322339
• Journal Information: Inorganic Chemistry, Vol. 55, Issue 13; ISSN 0020-1669
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
thermal conductivity
heat capacity
diffusion
chemical structure
physical and chemical processes