Effects of P Doping in Nd₂Fe₁₇ and Phase Diagram of Fe Rich Nd–Fe–P

It was found that a P-doping process occurs in Nd₂Fe₁₇ by gas phase reaction around 673 K. A decrease of the lattice constants a and c by up to ≈︂0.6 and ≈︂0.8%, respectively, and an increase of the Curie temperature by up to ≈︂30 K were observed. The P-doped 2:17 phase dissolves around 763 K. Four phase regions in the phase diagram of Fe rich Nd–Fe–P alloys below 1223 K were determined. The phases in each region are: A: Nd₂Fe₁₇ + α-Fe + NdP; B: α-Fe + NdP + Nd₂Fe₁₂P₇; C: α-Nd₂Fe₁₂P₇ + Fe₃P; D: Nd₂Fe₁₂P₇ + Fe₂P + Fe₃P. The variation of the lattice constants with composition of the alloys is as large as (Δa/a)_max ≈︂ 0.8% for NdP and (Δa/a)_max ≈︂ 1.2% and (Δc/c)_max ≈︂ 0.8% for Nd₂Fe₁₂P₇ suggesting a certain soluble range for the compounds.