Standard enthalpies of formation of selected XYZ half-Heusler compounds

The standard enthalpies of formation of selected ternary half-Heusler type compositions XYZ (X = Au, Co, Fe, Ir, Ni, Pd, Pt, Rh, Ru; Y = Hf, Mn, Ti, Zr; Z = Ga, Sn) were measured using high temperature direct reaction calorimetry. The measured standard enthalpies of formation (in kJ/mole of atoms) of the half-Heusler compounds (prototype MgAgAs, Pearson symbol cF12, space group F-43m) are, IrMnSn (-29.4 +/- 1.8); NiTiSn (-52.6 +/- 2.4); PtHfSn (-98.8 +/- 3.4); PtMnSn (-55.8 +/- 2.6); PtTiSn (-93.6 +/- 3.3); PtZrSn (-104.9 +/- 3.8); for the B2 compound (prototype CsCl, Pearson symbol cP2, space group Pm-3m), RuMnGa (-26.9 +/- 1.7); for the C1 structured (prototype CaF2, Pearson symbol cF12, space group Pm-3m) or the C1(b) structured compound IrMnGa (-40.9 +/- 1.7). Indicative standard enthalpies of formation of the following compounds were obtained, half-Heusler compounds AuMnSn, CoTiSn, IrZrSn, NiHfSn, NiZrSn, PdHfSn, PdZrSn, RhTiSn; Heusler compound (prototype Cu2MnAl, Pearson symbol cF16, space group Fm-3m) RhMnSn; hexagonal compound (prototype BeZrSi, Pearson symbol hP6, space group P6(3)/mmc) PtMnGa and another type of hexagonal compound (prototype RhHfSn, Pearson symbol hP18, space group P-62c) RhHfSn, IrZrsn, RhZrSn. Values were compared with ab initio calculations from AFLOW and OQMD. Lattice parameters of these compounds were determined using X-ray diffraction (XRD) analysis. Microstructures were characterized using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Selected alloys were further annealed to investigate phase transformations and phase relationships. Published by Elsevier Ltd.