A High‐Temperature Neutron Diffraction and First‐Principles Study of Ti 3 AlC 2 and Ti 3 ( Al 0.8 Sn 0.2 ) C 2

Herein, we report on the temperature‐dependent crystal structures of Ti 3 AlC 2 and Ti 3 Al 0.8 Sn 0.2 C 2 in the 373–1273 K temperature range, as determined by Rietveld analysis of high‐temperature neutron diffraction time‐of‐flight data. The compositions are 86(1) wt% Ti 3 AlC 2 and 14(1) wt% TiC 0.92(2) for the sample with no Sn , and 95(1) wt% Ti 3 ( Al 0.8 Sn 0.2 ) C 2 and 5(1) wt% Ti 2 AlC for the solid solution with Sn . The average linear volumetric thermal expansion is 8.0(2) × 10 −6  K − 1 for Ti 3 AlC 2 and 8.2(5) × 10 −6  K −1 for Ti 3 ( Al 0.8 Sn 0.2 ) C 2 . The average linear thermal expansion in the a and c directions, respectively, are 7.6(2) × 10 −6  K −1 and 8.9(2) × 10 −6  K −1 for Ti 3 AlC 2 . For Ti 3 ( Al 0.8 Sn 0.2 ) C 2 , the respective values are 8.0(5) × 10 −6  K −1 and 8.6(6) × 10 −6  K −1 . In the case of the solid solution, the quadratic thermal expansion coefficients are also given. Detailed bond lengths analysis shows that the thermal expansions along the a and c directions are controlled by the thermal expansions of the Ti – C , and Ti – Al bond lengths, respectively. The atomic displacement parameters (ADPs) show that the Al and Sn atoms vibrate with a higher amplitude than the Ti and C atoms. Consistent with first‐principles calculations, the ADPs of the Al/Sn site(s) in Ti 3 ( Al 0.8 Sn 0.2 ) C 2 are lower than the ADPs of Al in Ti 3 AlC 2 .