Experimental synthesis and density functional theory investigation of radiation tolerance of Zr₃(Al_{1- x}Si_x)C₂ MAX phases

Synthesis, characterization and density functional theory calculations have been combined to examine the formation of the Zr₃(Al_{1– x}Si_x)C₂ quaternary MAX phases and the intrinsic defect processes in Zr₃AlC₂ and Zr₃SiC₂. The MAX phase family is extended by demonstrating that Zr₃(Al_{1– x}Si_x)C₂, and particularly compositions with x≈0.1, can be formed leading here to a yield of 59 wt%. It has been found that Zr₃AlC₂ - and by extension Zr₃(Al_{1– x}Si_x)C₂ - formation rates benefit from the presence of traces of Si in the reactant mix, presumably through the in situ formation of Zr_ySi_z phase(s) acting as a nucleation substrate for the MAX phase. To investigate the radiation tolerance of Zr₃(Al_{1– x}Si_x)C₂, we have also considered the intrinsic defect properties of the end-members. A-element Frenkel reaction for both Zr₃AlC₂ (1.71 eV) and Zr₃SiC₂ (1.41 eV) phases are the lowest energy defect reactions. For comparison we consider the defect processes in Ti₃AlC₂ and Ti₃SiC₂ phases. It is concluded that Zr₃AlC₂ and Ti₃AlC₂ MAX phases are more radiation tolerant than Zr₃SiC₂ and Ti₃SiC₂, respectively. Their applicability as cladding materials for nuclear fuel is discussed.