Recently, Yanson et al. [2001Yan] studied the phase relationships in this system at 500 deg C in a narrow region around 10.5 at. percent Tb. Here, the structurally related phases of the types Th_2Ni_(17), Th_2Zn_(17), and TbCu_7 occur close to one another. The Al-Fe phase diagram [1993Kat] shows that the face-centered-cubic (fcc) solid solution based on Fe is restricted by a gamma loop. The body-centered-cubic (bcc) solid solution alpha exists in the disordered A2 form, as well as the ordered B2 and D0_3 forms and extends up to 50 at. percent Al at the temperature of interest here (500 deg C). In the Fe-Tb system [1993 Oka], there are four intermediate phases. The Th_2Ni_(17)-type hexagonal phase Tb_2Fe_(17) (denoted here 2: 17H) is stable at stoichiometric and at Fe-rich compositions and the Th_2Ni_(17)-type rhombohedral phase 2:17R is stable at Tb-rich compositions [2001 Yan]. The other three phases are the Th_6Mn_(23)-type cubic phase Tb_6Fe_(23), the PuNi_3-type rhombohedral phase TbFe_3, and the MgCu_2-type cubic phase TbFe_2.
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