If Heusler TiNi₂Sn precipitates are to impede the conduction of heat in thermoelectric TiNiSn, the interfaces between these should ideally be well-matched at the interface thermally robust. To illustrate this requirement, MBE growth of these materials has been achieved, allowing controllable, sharp interfaces, as seen in the accompanying scanning transmission electron micrograph. Significantly, the interfaces are stable even after annealing at 500 °C for 6 h. This has important implications for the robustness of biphasic thermoelectrics made from these relatively inexpensive materials.