halfHeusler

Half-Heusler compounds are a family of intermetallics with the chemical formula XYZ, where X and Y are typically transition metals or rare-earth elements and Z is a main-group element. They crystallize in the cubic C1b structure, a derivative of the full Heusler L21 structure in which one of the four interpenetrating sublattices is vacant, yielding a 1:1:1 stoichiometry and a single vacant site.

The structure consists of three interpenetrating face-centered cubic sublattices with one lattice site deliberately left empty, giving rise to the characteristic XYZ arrangement. This structural feature distinguishes half-Heuslers from full Heuslers. Typical examples include NiTiSn, CoTiSb, and CoMnSb, though many combinations of X, Y, and Z are known. The properties of the compounds are highly tunable by changing the constituent elements and by deliberate doping.

Electronic properties span semiconducting, semimetallic, and magnetic behaviors. Many members are semiconductors with relatively small band gaps, and the total valence electron count often favors semiconducting behavior near an 18-electron rule. Doping and alloying tune carrier type and concentration, making half-Heuslers attractive as thermoelectric materials with high Seebeck coefficients and reduced thermal conductivity. Some members also exhibit magnetism or nontrivial band topology, positioning them as candidates for spintronics and topological quantum materials. Under pressure or with chemical substitution, certain compounds can show superconductivity.

Synthesis methods include arc melting, solid-state synthesis with subsequent annealing, and flux growth for single crystals. The combination of tunable chemistry, structure, and properties makes half-Heuslers a versatile platform in thermoelectrics, magnetism, and quantum materials research.