Doping-Induced Polymorph and Carrier Polarity Changes in Thermoelectric Ag(Bi,Sb)Se₂ Solid Solution

Abstract

Silver bismuth diselenide (AgBiSe 2 ) is an n-type thermoelectric material that exhibits a complex structural phase transition from the hexagonal to cubic phase, while silver antimony diselenide (AgSbSe 2 ) is a p-type thermoelectric material that crystallizes in the cubic phase at all temperatures. Here, we investigate the crystal structure and thermoelectric properties of Ag(Bi,Sb)Se 2 solid solution, employing AgBi 0.9 Sb 0.1 Se 2 and AgBi 0.7 Sb 0.3 Se 2 as representative samples. The carrier polarity of AgBi 0.9 Sb 0.1 Se 2 is converted from the n-type to ptype by Pb doping, accompanied by a polymorphic change to the cubic phase. It is difficult to obtain highly conductive p-type hexagonal AgBiSe 2 -based materials, although first-principles calculations predict high-performance thermoelectric properties for these systems. We also demonstrate that cubic AgBi 0.7 Sb 0.3 Se 2 undergoes a polymorphic change to the hexagonal phase upon Nb doping. The present study show that polymorphic changes inevitably occurred upon Pb/Nb doping to optimize thermoelectric properties of Ag(Bi,Sb)Se 2 solid solution.

Structural Phase Transition and Related Thermoelectric Properties in Sn Doped AgBiSe2

“…The room-temperature Seebeck coefficient of Ag 0.90 Bi 0.90 Sn 0.20 Se 2 is about +130 µV/K, while that of Ag 0.875 Bi 0.875 Sn 0.25 Se 2 increases to about +350 µV/K. A similar carrier type transition behaviour has been observed in AgBi 1-x Sb x Se 2 [33,34]. With increasing temperature, the Seebeck coefficients of the Ag 1−x/2 Bi 1−x/2 Sn x Se 2 samples are converted into n-type negative values.…”

“…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].…”

Superconducting properties of high-entropy-alloy tellurides M-Te (M: Ag, In, Cd, Sn, Sb, Pb, Bi) with a NaCl-type structure

“…According to the charge neutrality in a NaCl-type telluride, the valence state of the metal site should be +2. Basically, the valence state of Sb and Bi tend to be +3 in a NaCl-type structure [14,15]; hence, Sb 3+ and Bi 3+ should be incorporated in the tellurides with Ag + to make the average valence +2. Therefore, we determined the composition to be studied with a restriction that five metals are included, and all the phases contain Ag-Bi or Ag-Sb to satisfy the HEA condition at the metal site.…”