Abstract
Herein, we report on the crystal structures of Nb2AlC and TiNbAlCactual composition (Ti-0.45,Nb-0.55)(2)AlCcompounds determined from Rietveld analysis of neutron diffraction patterns in the 300-1173K temperature range. The average linear thermal expansion coefficients of a Nb2AlC sample in the a and c directions are, respectively, 7.9(5)x10(-6) and 7.7(5)x10(-6)K(-1) on one neutron diffractometer and 7.3(3)x10(-6) and 7.0(2)x10(-6)K(-1) on a second diffractometer. The respective values for the (Ti-0.45,Nb-0.55)(2)AlC compositiononly tested on one diffractometerare 8.5(3)x10(-6) and 7.5(5)x10(-6)K(-1). These values are relatively low compared to other MAX phases. Like other MAX phases, however, the atomic displacement parameters (APDs) show that the Al atoms vibrate with higher amplitudes than the Ti and C atoms, and more along the basal planes than normal to them. When the predictions of the APDs obtained from density functional theory are compared to the experimental results, good quantitative agreement is found for the Al atoms. In case of the Nb and C atoms, the agreement was more qualitative.
