Electronic structures and thermal properties of 312-MAX phases
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
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.
Sam Azadi and MW Finnis, "Electronic structures and thermal properties of 312-MAX phases" in "Ultra-High Temperature Ceramics: Materials for Extreme Environment Applications IV", Jon Binner, The University of Birmingham, Edgbaston, United Kingdom Bill Lee, Imperial College, London, United Kingdom Eds, ECI Symposium Series, (2017). http://dc.engconfintl.org/uhtc_iv/48