The crystal structure and phase transition of Hf₂Pt₃

The structure of Hf₂Pt₃ has been re-investigated using transmission electron microscopy and Rietveld refinement of neutron powder diffraction data at temperatures up to 1500°C. This compound does not belong to the MoSi₂ structure type as previously reported, but instead is isostructural with Ti₂Pd₃ and the low-temperature form of Ti₂Ni₃. The crystal structure is orthorhombic (pseudo-tetragonal), Cmcm, Z = 4, with a = 14.653(1) Å, b = 4.8741(3) Å, and c = 4.8671(3) Å at room temperature. The b/c ratio decreases from 1.0014(2) at room temperature to 1.0005(3) at 1500°C, but the material does not transform to the high-temperature form of Ti ₂Ni₃ (I4/mmm) under the conditions studied. The electron diffraction data indicate multiple stacking faults as well as short-range order. On heating above 1630°C there is a phase transition to a B2-related structure with a ≈ 3.315(1) Å at 1659°C.