The system Nd–Fe–Sb: Phase equilibria, crystal structures and physical properties

Phase equilibria within the isothermal section of the ternary system Nd–Fe–Sb were derived at 800 °C by using X-ray powder diffraction, light optical microscopy and electron probe microanalysis. Crystal structures of the ternary compounds Nd2Fe7−xSb6−y (τ2-orthorhombic), Nd2Fe5−xSb10−y (τ2-tetragonal) Nd3Fe3Sb7 (τ3) and NdFeSb3 (τ4) were determined by single crystal X-ray diffraction and by Rietveld X-ray powder data refinement. The phase τ2 was found to exhibit two modifications, orthorhombic (Nd2Fe7−xSb6−y-type, S.G. Immm, a = 0.42632(6) nm, b = 0.43098(7) nm, c = 2.5823(3) nm) and tetragonal (La2Fe5−xSb10−y-type, S.G. I4/mmm, a = 0.42897(2) nm, c = 2.5693(4) nm). Tetragonal and orthorhombic modifications form a crystallographic group–subgroup relation and are closely related to the Zr3Cu4Si6-type. Nd3Fe3Sb7 (τ3) crystallizes with a unique structure type (S.G. P63/m, a = 1.31808(3) nm, c = 0.41819(3) nm), which is isopointal to the Cu10Sb3-type. NdFeSb3 (τ4) adopts the LaPdSb3-type. Physical properties comprising magnetization, resistivity and specific heat were measured for RE2Fe5−xSb10−y (RE = Ce, Nd), NdFeSb3 and Nd3Fe3Sb7. NdFeSb3 orders antiferromagnetically below 3.0 K due to the presence of magnetic moments on Nd sites. For the other compounds a more complex magnetic behaviour is observed at low temperatures that may be related to the contributions coming from both the rare earth and iron sublattices.