As in previous sections we mainly focus on the averaged ZT . The ZT max for both p-and n-type doping of the four Ge chalcogenides and Pnma SnS/SnSe, at temperatures below the reported phase transition temperatures (GeS: 863 K, GeSe: 907 K, SnS: 878 K, SnSe: 750 K ) are summarised in Table .