Thermal properties of Ti4AlN3

In this article we report on the atomic displacement parameters, lattice ex pansions, heat capacity, and thermal conductivity of samples of Ti4AlN3 in the 298-1370 K temperature range. Rietveld refinement of high temperature n eutron diffraction data shows that the nitrogen is substoichiometric and th e formula is Ti4AlN2.9. In this structure, the atomic displacement paramete rs of the Al atoms are higher than those of either the Ti or N atoms. The T i-N bonds adjacent to the Al planes are about 2.5% shorter than the Ti-N bo nds in the inner layers. The thermal expansion coefficients along the a and c axes are, respectively, (9.6 +/- 0.1)x10(-6) and (8.8 +/- 0.1)x10(-6) K- 1. The unit cell expansivity, (9.4 +/- 0.1)x10(-6) K-1, is in agreement wit h the dilatometric bulk thermal expansivity (9.7 +/- 0.2)x10(-6) K-1. The h eat capacity, c(p), is 150 J/mol K at ambient temperatures and extrapolates to approximate to 220 J/mol K at 1300 K. At all temperatures c(p) equals f our times the molar heat capacity of TiN. The room temperature thermal cond uctivity is 12 W/m K and increases linearly to approximate to 20 W/m K at 1 300 K. (C) 2000 American Institute of Physics. [S0021-8979(00)04212-2].