Thermal Conductivity, Electrical Resistivity, and Seebeck Coefficient of Uranium Mononitride

Abstract

Measurements are reported for the thermal conductivity, λ(80° to 400°K), electrical resistivity, ρ(4.2° to 400°K), and absolute Seebeck coefficient, Q(6° to 400°K), of pressed and sintered uranium mononitride. The measurements between 77° and 400°K were made using an absolute longitudinal heat flow apparatus. These data and literature values for the thermal conductivity and electrical resistivity at higher temperatures were used to separate the electronic and lattice portions of the thermal conductivity. The results indicate that the lattice conductivity peaks in the range 250° to 300°K and that the high-temperature limit of the Lorenz function may be greater than the Sommerfeld value of 2.443 × 10-8 (V2°K-2). The electrical resistivity and the absolute Seebeck coefficient exhibit sharp slope changes near the Neel temperature, TN(∼50° to 60°K). The Seebeck coefficient has a minimum at 34°K and then rises to a local maximum at 10°K. This low-temperature peak is probably due to magnon drag. The temperature dependence of the electrical resistivity is dominated by the magnetic contribution which increases as T2.38±0.08 between 10° and 52°K. The magnetic contribution is constant at high temperatures with an estimated value of 142 μΩ-cm.