Effect of R-site substitution and the pressure on stability of RFe12: A first-principles study

We theoretically study the structural stability of RFe12 with the ThMn12 structure (R: rare-earth element, La, Pr, Nd, Sm, Gd, Dy, Ho, Er, Tm, Lu, Y, or Sc, or group-IV element, Zr or Hf) based on density functional theory. The formation energy has a strong correlation with the atomic radius of R. The formation energy relative to simple substances decreases as the atomic radius decreases, except for R= Sc and Hf, while that relative to R2Fe17 and bcc Fe has a minimum for R= Dy. The present results are consistent with recent experimental reports in which the partial substitution of Zr at R sites stabilizes RFe12-type compounds with R= Nd or Sm. Our results also suggest that the partial substitution of Y, Dy, Ho, Er, or Tm for Nd or Sm is a possible way to enhance the stability of the ThMn12 structure. Under hydrostatic pressure, the formation enthalpy decreases up to ≈6 GPa and then starts to increase at higher pressures.