MgPdSb-An Electron-Deficient Half-Heusler Phase

The half-Heusler family consists of many semi-conducting intermetallic compounds, virtually all of them having a valence electron count (VEC) of 18. We have studied an electron-deficient (VEC = 17) phase MgPdSb and its Pd-stuffed variant MgPd1.25Sb. The cubic F (4) over bar 3m crystal structure was confirmed by the Rietveld refinement of powder X-ray diffraction (XRD) data. The lattice parameter is a = 6.284 and 6.335 angstrom for MgPdSb and MgPd1.25Sb, respectively. The Debye temperature and Sommerfeld coefficient for MgPdSb are Theta(D) = 282 K and gamma = 3.3 mJ mol(-1) K-2, respectively, and are similar to those obtained for MgPd1.25Sb. There is neither phase transition nor superconductivity observed above 1.8 K. The differences between the electronic structures of Mg-based half-Heusler compounds make them robustly metallic, irrespective of the electron count and the introduction of interstitial transition metal (Pd) atoms.