ECI Digital Archives

Title

Electronic structures and thermal properties of 312-MAX phases

Authors

Sam Azadi, Imperial College London, UKFollow
MW Finnis, Imperial College London, UK

Conference Dates

September 17-20, 2017

Abstract

The "M_n+1AX_n 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 M_n+1AX_n, 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.

Recommended Citation

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). https://dc.engconfintl.org/uhtc_iv/48