Ni atomic disorder in ZrNiSn revealed by scanning transmission electron microscopy

Atomic disorders and defects in thermoelectric semiconductors can significantly affect their electronic and phonon transport. In this work, we report the studies of Ni atomic disorder in ZrNiSn by scanning transmission electron microscopy. Three different ZrNiSn polycrystalline and single-crystalline samples were synthesized under different processes from thermodynamically non-equilibrium conditions to more equilibrium ones, as demonstrated by characterizing their phase structure and transport properties. Atomic-resolution high-angle annular-dark-field scanning transmission electron microscopy was employed to study the Ni atomic disorder. The polycrystalline sample prepared by levitation melting exhibited a strong local composition fluctuation, while the sample after further long-term annealing and the single crystal exhibited a more uniform distribution of Ni at the 4c and 4d sites. These results reveal the evolution of Ni atomic disorder in different samples that were prepared under different thermodynamic conditions, which will be helpful to understand the Ni atomic disorder and its relationship with thermoelectric transport in the representative half-Heusler system ZrNiSn.