Thermal and electrical properties of Nb2AlC, (Ti, Nb)2AlC and Ti2AlC

Abstract

The heat capacities, thermal-expansion coefficients, thermal and electrical conductivities of Nb2AlC (actual Nb:Al:C mole fractions: 0.525 ± 0.005, 0.240 ± 0.002, and 0.235 ± 0.005, respectively), Ti2AlC and (Ti, Nb)2AlC (actual Ti:Nb:Al:C mole fractions: 0.244 ± 0.005, 0.273 ± 0.005, 0.240 ± 0.003, and 0.244 ± 0.005, respectively) were measured as a function of temperature. These ternaries are good electrical conductors, with a resistivity that increases linearly with increasing temperatures. The resistivity of (Ti, Nb)2AlC is higher than the other members, indicating a solid-solution scattering effect. The thermal-expansion coefficients, in the 25°C to 1000°C temperature range, are comparable and fall in the narrow range of 8.7 to 8.9 × 10-6 K-1, with that of the solid solution being the highest. They are all good conductors of heat, with thermal conductivities in the range between 15 to 45 W/m K at room temperature. The electronic component of the thermal conductivity is the dominant mechanism at all temperatures for Nb2AlC and (Ti, Nb)2AlC. The conductivity of Ti2AlC, on the other hand, is high because the phonon contribution to the conductivity is nonnegligible.