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Ye et al. J Mater Inf 2023;3:15 https://dx.doi.org/10.20517/jmi.2023.08 Page 27 of 37

Figure 20. The calculated (A) heat capacity, (B) the entropy of formation, and (C) the enthalpy difference of Fe Lu with the
2
experimental data [101] and the calculations [90] .

Figure 21. Calculated Fe-Y binary phase diagram with (A) the calculations [127,131-133] and (B) the experimental data [115] .

Figure 30 displays the calculated enthalpy of formation of the Fe-RE intermetallic compounds at 298 K (e.g.,
Fe RE , Fe RE , Fe RE, Fe RE, and Fe RE ). The enthalpy of formation Fe RE is the most negative and
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17
2
6
2
23
3
2
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shows a trend that the enthalpy of formation of Fe RE becomes increasingly negative with the RE atomic
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number increases in the Fe-RE (apart from Fe-Y, Fe-Gd, and Fe-Dy) binary systems. It is noted that the
enthalpy of formation of the Fe-Gd intermetallic compounds is more negative than those of the Fe-Tb
intermetallic compounds. In particular, the enthalpy of formation of the Fe-Y intermetallic compounds is
between that of the Fe-Sm intermetallic compounds and that of the Fe-Gd intermetallic compounds. There
[24]
[139]
are similar irregularities that also appear in the RE-B , RE-Mn [137,138] , and RE-Ni binary systems.
Generally, the enthalpy of formation of the Fe-RE intermetallic compounds become increasingly negative
with an increasing of the RE atomic number. It indicates stronger bond in Fe-RE (apart from Fe-Y) binary
systems as a consequence of the reducing atomic radius with the increasing of the RE atomic number.