Standard enthalpies of formation of selected Ni₂YZ Heusler compounds

The standard enthalpies of formation (Δ_fH°) of selected ternary Ni-based Heusler compounds Ni₂YZ (Y = Co, Cu, Fe, Hf, Mn, Ti, V; Z = Al, Ga, In, Si, Ge, Sn) were measured using high temperature direct reaction calorimetry. The measured standard enthalpies of formation (in kJ/mole of atoms) of the Heusler structured (L2₁, prototype Cu₂MnAl, Pearson symbol cF16, space group Fm3(-) m) compounds are: Ni₂MnGa (-29.8 ± 3.9); Ni₂MnIn (-24.5 ± 2.0); Ni₂MnSn (-29.7 ± 2.9); Ni₂TiGa (-42.5 ± 2.2); Ni₂TiIn (-28.5 ± 1.1); Ni₂TiSn (-46.8 ± 2.0), for the B2 compound (prototype CsCl, Pearson cP2, space group Pm3(-) m): Ni₂MnAl (-32.0 ± 2.8), for the inverse Heusler structured (i-L2₁, prototype Li₂AgSb, Pearson symbol cF16, space group F4(-) 3 m) compound: Ni₂CuSn (-12.5 ± 2.1), for the compounds of the L1₂ (prototype AuCu₃, Pearson symbol cP4, space group Pm3(-) m) structure: Ni₂CuAl (-38.9 ± 3.1); Ni₂FeGe (-25.8 ± 3.0). Several off-stoichiometric alloys in the Ni-Mn-Sn system were also investigated: Ni_0.55Mn_0.20Sn_0.25 (-26.6 ± 1.0); Ni_0.45Mn_0.30Sn_0.25 (-27.5 ± 2.6); Ni_0.40Mn_0.35Sn_0.25 (-26.6 ± 2.6); Ni_0.25Mn_0.50Sn_0.25 (-20.9 ± 2.6); Ni_0.50Mn_0.30Sn_0.20 (-21.0 ± 3.2); Ni_0.50Mn_0.35Sn_0.15 (-20.1 ± 1.7). Values are compared with those from first principles calculations in published papers and the Open Quantum Materials Database (OQMD). Lattice parameters were determined using X-ray diffraction analysis. Microstructures were characterized using scanning electron microscopy (SEM) with an energy dispersive spectrometer (EDS). Differential scanning calorimetry (DSC) was used to measure the melting points of the compounds.