10.1021/acs.inorgchem.6b00826.s001

Gd<sub>12</sub>Co<sub>5.3</sub>Bi and Gd<sub>12</sub>Co<sub>5</sub>Bi, Crystalline Doppelgänger with Low Thermal Conductivities

Abstract

Attempts to prepare Gd<sub>12</sub>Co<sub>5</sub>Bi, a member of the rare-earth (RE) intermetallics RE<sub>12</sub>Co<sub>5</sub>Bi, which were identified by a machine-learning recommendation engine as potential candidates for thermoelectric materials, led instead to formation of the new compound Gd<sub>12</sub>Co<sub>5.3</sub>Bi 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 Gd<sub>12</sub>Co<sub>5.3</sub>Bi and Gd<sub>12</sub>Co<sub>5</sub>Bi are distinct phases. The higher symmetry structure of Gd<sub>12</sub>Co<sub>5.3</sub>Bi (cubic, space group <i>Im</i>3̅, <i>Z</i> = 2, <i>a</i> = 9.713(6) Å), as determined from single-crystal X-ray diffraction, is closely related to that of Gd<sub>12</sub>Co<sub>5</sub>Bi (tetragonal, space group <i>Immm</i>). Single Co atoms and Co–Co dumbbells are disordered with occupancies of 0.78(2) and 0.22(2), respectively, in Gd<sub>12</sub>Co<sub>5.3</sub>Bi, but they are ordered in Gd<sub>12</sub>Co<sub>5</sub>Bi. Consistent with this disorder, the electrical resistivity shows less dependence on temperature for Gd<sub>12</sub>Co<sub>5.3</sub>Bi than for Gd<sub>12</sub>Co<sub>5</sub>Bi. The thermal conductivity is low and reaches 2.8 W m<sup>–1</sup> K<sup>–1</sup> at 600 °C for both compounds; however, the temperature dependence of the thermal conductivity differs, decreasing for Gd<sub>12</sub>Co<sub>5.3</sub>Bi and increasing for Gd<sub>12</sub>Co<sub>5</sub>Bi as the temperature increases. The unusual trends in thermal properties persist in the heat capacity, which decreases below 2<i>R</i>, and in the thermal diffusivity, which increases at higher temperatures

Similar works

Full text

thumbnail-image
oai:figshare.com:article/3436871Last time updated on 2/12/2018

This paper was published in FigShare.

Having an issue?

Is data on this page outdated, violates copyrights or anything else? Report the problem now and we will take corresponding actions after reviewing your request.