Combined ab initio and experimental screening of phase stabilities in the Ce-Fe-Ti- X system ( X=3d and 4d metals)

Abstract

One of the main challenges for the synthesis and application of the promising hard-magnetic compound $\mathrm{Ce}{\mathrm{Fe}}_{11}\mathrm{Ti}$ is the formation of Laves phases that are detrimental for their thermodynamic stability and magnetic properties. In this paper, we present an ab initio based approach to modify the stability of these phases in the Ce-Fe-Ti system by additions of $3d$ and $4d$ elements. We combine highly accurate free-energy calculations with an efficient screening technique to determine the critical annealing temperature for the formation of $\mathrm{Ce(Fe,X)}{}_{11}\mathrm{Ti}$. The central findings are the dominant role of the formation enthalpy at $T=0$ K on chemical trends and the major relevance of partial chemical decompositions. Based on these insights, promising transition metals to promote the stability of the hard-magnetic phase, such as Zn and Tc, were predicted. The comparison with suction casting and reactive crucible melting experiments for Ce-Fe-Ti-X (X = Cu, Ga, Co, and Cr) highlights the relevance of additional phases and quaternary elements.