Effect of R-site substitution and the pressure on stability of RFe 12: A first-principles study

We theoretically study the structural stability of RFe 12 with the ThMn 12 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 R 2Fe 17 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 RFe 12-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 ThMn 12 structure. Under hydrostatic pressure, the formation enthalpy decreases up to ≈6 GPa and then starts to increase at higher pressures.We theoretically study the structural stability of RFe 12 with the ThMn 12 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 R 2Fe 17 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 RFe 12-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 ThMn 12 structure. Under hydrostatic pressure, the formation enthalpy decreases up to ≈6 GPa and then starts to increase at higher pressures.

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