Theoretical Study on the Mechanism of Anisotropic Thermal Properties of Ti2 AlC and Cr2 AlC.

Temperature dependences of thermal and elastic properties, such as the Grüneisen parameters, thermal expansion, bulk modulus, and heat capacity of Ti2 AlC and Cr2 AlC, are studied by combining first-principles method and lattice dynamic calculation based on the quasi-harmonic model. Experimental thermal expansion coefficient is also measured for comparison. Thermal expansion coefficients of Ti2 AlC and Cr2 AlC show different trends: Ti2 AlC exhibits anisotropic thermal expansion while Cr2 AlC shows generally isotropic character. The mechanism is explored by investigating the isotropy or anisotropy of Grüneisen parameters (phonon anharmonicity and thermal pressure) and elastic stiffness (response to thermal pressure) of Ti2 AlC and Cr2 AlC. In addition, the calculated bulk modulus of Cr2 AlC is higher at ambient temperature but decreases faster than the value of Ti2 AlC as temperature increasing. [ABSTRACT FROM AUTHOR]