Thermal properties of Ti₄AlN₃

In this article we report on the atomic displacement parameters, lattice expansions, heat capacity, and thermal conductivity of samples of Ti₄AlN₃ in the 298-1370 K temperature range. Rietveld refinement of high temperature neutron diffraction data shows that the nitrogen is substoichiometric and the formula is Ti₄AlN_2.9. In this structure, the atomic displacement parameters of the Al atoms are higher than those of either the Ti or N atoms. The Ti-N bonds adjacent to the Al planes are about 2.5% shorter than the Ti-N bonds in the inner layers. The thermal expansion coefficients along the a and c axes are, respectively, (9.6±0.1) × 10^-6 and (8.8±0.1) × 10^-6 K^-1. The unit cell expansivity, (9.4±0.1) × 10^-6 K^-1, is in agreement with the dilatometric bulk thermal expansivity (9.7 ± 0.2) × 10^-6K^-1. The heat capacity, c_p, is 150 J/mol K at ambient temperatures and extrapolates to ≈220 J/mol K at 1300 K. At all temperatures c_p equals four times the molar heat capacity of TiN. The room temperature thermal conductivity is 12 W/m K and increases linearly to ≈20 W/m K at 1300 K.