Phase diagram of the Nd₂Fe₁₄B-Sm₂Fe₁₄B pseudo-binary system

The phase relations in the (1-x)Nd₂Fe₁₄B-xSm₂Fe₁₄B system over the whole concentration range have been studied by means of X-ray powder diffraction (XRD), differential thermal analysis (DTA) and scanning electron microscopy with energy-dispersive X-ray spectroscopy. Crystal structure parameters for all studied compositions of (Nd_1-xSm_x)₂Fe₁₄B have been determined by full-profile Rietveld refinements. These results revealed that all intermediate alloys of (Nd_1-xSm_x)₂Fe₁₄B are similar to the end member of the investigated system, Nd₂Fe₁₄B, with a tetragonal structure (space group P4₂/mnm). The formation of continuous solid solutions has been found in this system. The normalized lattice parameters and unit-cell volumes of (Nd_1-xSm_x)₂Fe₁₄B solid solutions decrease linearly with increasing Sm content. The DTA measurements show that the melting temperature of (Nd_1-xSm_x)₂Fe₁₄B increases linearly with increasing Sm content and no metastable phases were detected. Based on the DTA data and XRD results, a tentative phase diagram for the pseudo-binary system Nd₂Fe₁₄B-Sm₂Fe₁₄B has been constructed.