Entropy Engineered Cubic n‐Type AgBiSe₂ Alloy with High Thermoelectric Performance in Fully Extended Operating Temperature Range

Abstract

Developing high performance n‐type thermoelectric (TE) materials is fundamentally important for developing high efficiency TE devices. AgBiSe2, which reveals superior n‐type TE performance in a cubic phase, crystallizes in a hexagonal phase at room temperature, and typically, undergoes phase transitions to a cubic phase at a temperature above 580 K. Here, for the first time, through entropy optimization with lead‐selenides (≥9.9 mol%), the high‐temperature cubic phase of AgBiSe2 is stabilized from 300 to 800 K. Furthermore, the AgBiSe2‐PbSe pseudo‐binary diagram is established. The resultant alloys with optimized entropy possess unique local distorted cubic lattices, which contribute low lattice thermal conductivity approaching 0.3 W m−1 K−1 in extended operating temperature range. Consequently, a peak figure of merit zT value of ≈0.8 at 800 K and a record‐high average zT value of 0.42 for n‐type I‐V‐VI2 compounds are attained in pure phase cubic n‐type (AgBiSe2)1−x(PbSe)x solid solutions. These results pave the way for developing new TE materials via entropy engineering.

High Entropy Semiconductor AgMnGeSbTe4 with Desirable Thermoelectric Performance

“…[18] In recent years, high entropy materials have attracted increasing attention from the thermoelectric community due to its high crystal symmetry and serious lattice distortion. [4,19,20] First, enhanced configuration entropy can improve the solubility of atoms and the stability of crystal structure (e.g., PbSe). [4] Second, high crystal symmetry is expected to enhance the electrical transport properties for thermoelectric materials (e.g., GeTe).…”

Structural Phase Transition and Related Thermoelectric Properties in Sn Doped AgBiSe2

“…However, it is very difficult to confirm this conjecture from theoretical calculations or experiment measurements due to the disordered atomic distribution of these materials. The electrical conductivity of Sn-doped AgBiSe 2 falls in the range from 110 S/cm to 150 S/cm at 773 K, which is comparable with cubic (AgBiSe 2 ) 1−x (PbSe) x [32]. Due to the change of carrier type, an extreme power factor (PF) value is observed at about 373 K. The maximum PF value of the Ag 1−x/2 Bi 1−x/2 Sn x Se 2 materials with p-type transport properties is about 0.8 µW/cm•K 2 , while Ag 0.875 Bi 0.875 Sn 0.25 Se 2 exhibits the maximum n-type PF value of~1.2 µW/cm•K 2 at 773 K.…”

“…Figure 6b shows the calculated κ latt + κ bip results in the range of 300 K to 773 K. Due to the enhanced point defects scattering, the lattice thermal conductivity of Sn-doped AgBiSe 2 is lower than that of pristine AgBiSe 2 in the range from 300 K to 523 K. The κ latt + κ bip values of Ag 0.9 Bi 0.9 Sn 0. [32][33][34]. This ultra-low κ latt + κ bip value can be explained by two reasons, namely the increased point defect scattering caused by doping Sn and the increased phonon-phonon scattering with increasing temperature.…”

“…Differential scanning calo- Inspired by the research on (AgBiSe2) 1−x (PbSe) x , we focus on another IV-A metal and find that a stabilized room-temperature cubic AgBiSe 2 phase can also be achieved via Sn substitution. In previous studies, both AgSbSe 2 and PbSe have cubic crystal structures, so it is not hard to understand the phase transition behavior in (AgBiSe 2 ) 1−x (AgSbSe 2 ) x and (AgBiSe 2 ) 1−x (PbSe) x solid solutions [32][33][34]. Herein, although the crystal structure of SnSe is not cubic [36], the solid solution between SnSe and AgBiSe 2 has a cubic structure at room temperature.…”

“…Both experimental and density functional theory calculation results indicate that p-type hexagonal AgBiSe 2 can potentially be used in room-temperature thermoelectric applications [30,31]. Additionally, the phase transition temperatures of AgBi 1−x Sb x Se 2 are determined by the doping concentration of Sb [32,33]. Very recently, Br-doped cubic (AgBiSe2) 0.7 (PbSe) 0.3 phase has been proved to be potential material with fine thermoelectric properties in the range from 300 to 800 K [34].…”