A computational quest for Nd2Fe14B-type Ce and Nd phases

We explore the formation of R2Fe14X (R = Ce, Nd; X = B, C, Al, Si, P, S, Ga, Ge, Zr, Sn) and R2Co14B (R = Ce, Nd) phases having the Nd2Fe14B structure type by means of density functional theory. Only R2Fe14X (R = Ce, Nd; X = B, C) and Nd2Co14B are known to form. Enthalpies of formation ΔHel are derived from calculated electronic total energies, and stability with respect to known binaries and ternaries is investigated to assess prospects for phase formation. With the exception of the X = Zr, Sn materials we find all compounds to be thermodynamically stable with respect to their constituent elements (ΔHel < 0). All of the hypothetical phases, however, are unstable relative to binary or other ternary compounds. The same holds true for the known compounds Ce2Fe14B and Ce2Fe14C, indicating that kinetic stabilization is also operative in this class of compounds. While our results strongly suggest that Ce2Co14B forms, the experimental literature is silent on its existence.