Theoretical Prediction and Synthesis of (Cr_2/3Zr_1/3)₂AlC <i>i</i>-MAX Phase

Abstract

Guided by predictive theory, a new compound with chemical composition (Cr_2/3Zr_1/3)₂AlC was synthesized by hot pressing of Cr, ZrH₂, Al, and C mixtures at 1300 °C. The crystal structure is monoclinic of space group C2/ c and displays in-plane chemical order in the metal layers, a so-called i-MAX phase. Quantitative chemical composition analyses confirmed that the primary phase had a (Cr_2/3Zr_1/3)₂AlC stoichiometry, with secondary Cr₂AlC, AlZrC₂, and ZrC phases and a small amount of Al-Cr intermetallics. A theoretical evaluation of the (Cr_2/3Zr_1/3)₂AlC magnetic structure was performed, indicating an antiferromagnetic ground state. Also (Cr_2/3Hf_1/3)₂AlC, of the same structure, was predicted to be stable.