STABLE AND METASTABLE PHASES IN PR-FE ALLOYS

It is shown by X-ray analysis and electron diffraction that in Pr - Fe alloys the metastable compounds PrFe2 of the MgZn2 (Cl4) and MgCu2 (C l5) types, which have not been observed earlier, are formed upon annea ling at 400 and 600 degrees C, in addition to the stable phases alpha- Pr and Pr2Fe17. The new compounds have the following lattice parameter s: PrFe2 (Cl4) - hexagonal lattice, space group P6(3)/mmc, a = 5.26 An gstrom, c = 8.62 Angstrom; PrFe2 (Cl5) - space group Fd3m, a = 6.76 An gstrom, Structure - orientation relationships between the above compou nds have been established. The transition to the stable state is accom panied by the structural transformation according to the scheme: PrFe2 (Cl4) --> PrFe2 (Cl5) --> Pr2Fe17. The equilibrium phase diagram of t he Pr-Fe system is presented.