Comparing the role of annealing on the transport properties of polymorphous AgBiSe(2) and monophase AgSbSe(2)

AgBiSe(2) and AgSbSe(2), two typical examples of Te-free I–V–VI(2) chalcogenides, are drawing much attention due to their promising thermoelectric performance. Both compounds were synthesized via melting and consolidated by spark plasma sintering. The role of annealing on the transport properties of polymorphous AgBiSe(2) and monophase AgSbSe(2) was studied. Annealing has a greater impact on AgBiSe(2) than AgSbSe(2), which is ascribed to the temperature dependent phase transition of AgBiSe(2). Unannealed AgBiSe(2) shows p–n switching, but annealed AgBiSe(2) exhibits n-type semiconducting behavior over the whole measurement temperature range. By performing high-temperature Hall measurements, we attribute this intriguing variation to the change in the amount of Ag vacancies and mid-temperature rhombohedral phase after annealing. Both AgBiSe(2) and AgSbSe(2) exhibit low thermal conductivity values, which are ∼0.40–0.50 W m(−1) K(−1) for AgSbSe(2) and ∼0.45–0.70 W m(−1) K(−1) for AgBiSe(2), respectively. The maximum ZT value of AgBiSe(2) is enhanced from 0.18 to 0.21 after annealing. Pristine AgSbSe(2) presents a ZT value as high as 0.60 at 623 K, although slight deterioration emerges after annealing.