Guest—Framework Interaction in Type I Inorganic Clathrates with Promising Thermoelectric Properties: On the Ionic versus Neutral Nature of the Alkaline-Earth Metal Guest A in A8Ga16Ge30 (A: Sr, Ba)
Sb doped Mg2Si0.4Sn0.6 materials feature with lots of dislocations at grain boundaries and plenty of nanoscale Mg2Si–Mg2Sn spinodal phases, both of which can scatter heat carrying phonons and suppress the bipolar effects, with a optimal ZT of 1.42.