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

Abstract

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 Nd 2Fe 7− x Sb 6− y (τ 2-orthorhombic), Nd 2Fe 5− x Sb 10− y (τ 2-tetragonal) Nd 3Fe 3Sb 7 (τ 3) and NdFeSb 3 (τ 4) were determined by single crystal X-ray diffraction and by Rietveld X-ray powder data refinement. The phase τ 2 was found to exhibit two modifications, orthorhombic (Nd 2Fe 7− x Sb 6− y -type, S.G. Immm, a = 0.42632(6) nm, b = 0.43098(7) nm, c = 2.5823(3) nm) and tetragonal (La 2Fe 5− x Sb 10− 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 Zr 3Cu 4Si 6-type. Nd 3Fe 3Sb 7 (τ 3) crystallizes with a unique structure type (S.G. P6 3/ m, a = 1.31808(3) nm, c = 0.41819(3) nm), which is isopointal to the Cu 10Sb 3-type. NdFeSb 3 (τ 4) adopts the LaPdSb 3-type. Physical properties comprising magnetization, resistivity and specific heat were measured for RE 2Fe 5− x Sb 10− y (RE = Ce, Nd), NdFeSb 3 and Nd 3Fe 3Sb 7. NdFeSb 3 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.