Anisotropic thermal conductivity in uranium dioxide

K Gofryk and S Du and CR Stanek and JC Lashley and XY Liu and RK Schulze and JL Smith and DJ Safarik and DD Byler and KJ McClellan and BP Uberuaga and BL Scott and DA Andersson, NATURE COMMUNICATIONS, 5, 4551 (2014).

DOI: 10.1038/ncomms5551

The thermal conductivity of uranium dioxide has been studied for over half a century, as uranium dioxide is the fuel used in a majority of operating nuclear reactors and thermal conductivity controls the conversion of heat produced by fission events to electricity. Because uranium dioxide is a cubic compound and thermal conductivity is a second-rank tensor, it has always been assumed to be isotropic. We report thermal conductivity measurements on oriented uranium dioxide single crystals that show anisotropy from 4 K to above 300 K. Our results indicate that phonon-spin scattering is important for understanding the general thermal conductivity behaviour, and also explains the anisotropy by coupling to the applied temperature gradient and breaking cubic symmetry.

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