Electronic structures and thermal properties of 312-MAX phases

Conference Dates

September 17-20, 2017


The "Mn+1AXn phases" (n=1,2, or 3) or "MAX phases", where M is a transition metal, A is an A- group element, and X is either C or N or both, exhibit particular chemical, physical, electrical, and mechanical properties. The unusual properties of the MAX phases can be linked to their layered structures and the nature of bonding. The M-X bonds are strong, while M-A bonds are relatively weak. These mixed metallic-covalent bondings are the source of many exceptional properties of the

MAX phases.

In this work we study a new discovered MAX phase of Zr3AlC2, which according to general formula of Mn+1AXn, it belongs to the "312" stoichiometry group. We employ Density Functional Theory (DFT)-based methods to obtain electronic structure and lattice dynamics properties. The quasi-harmonic approximation is used to calculate the Helmholtz free energy at temperature range from 10 < T < 1200 K. For the first time, we predict coefficient of thermal expansion for Zr3AlC2 MAX phase. We discuss details and technicalities which are required for accurate calculations of lattice vibration contribution to thermodynamic free energy.

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