Cu₂Te Incorporation-Induced High Average Thermoelectric Performance in p-Type Bi₂Te₃ Alloys

Abstract

p-Type (Bi, Sb) 2 Te 3 alloys are attractive materials for near-roomtemperature thermoelectric applications due to their high atomic masses and large spin−orbit interactions. However, their narrow band gaps originating from spin− orbit interactions lead to bipolar excitation, thereby limiting average thermoelectrics within a local temperature region (300−400 K). Here, we introduce Cu 2 Te into the Bi 0.3 Sb 1.7 Te 3 (BST) lattice to implement high thermoelectrics over a wide temperature range. The carrier concentration is synergistically modulated via Cu substitution and the evolution of intrinsic point defects (antisites and vacancies). Furthermore, the chain effect caused by Cu 2 Te incorporation in BST is reflected in the improvement of the weighted mobility μ W , thereby enhancing the power factor in the whole temperature range. Extrinsic and intrinsic defects due to the incorporation of Cu 2 Te lead to a significant reduction in the lattice thermal conductivity κ L , which is further demonstrated by Raman spectroscopy. Combining κ L and μ W , the quantity factor B increases from 0.5 to 1 with increasing Cu 2 Te content due to not only the reduction of κ L but also a significant improvement in electrical properties. Eventually, a peak figure of merit (zT) of ∼1.15 at 423 K is achieved in BST-Cu 2 Te samples, and an average figure of merit (zT ave ) of ∼1.12 (350−500 K) surpasses other excellent p-type Bi 2 Te 3 -based thermoelectrics. Such a synergistic effect can facilitate near-room-temperature thermoelectric applications of Bi 2 Te 3 -based alloys and provide chances for the technology space in thermoelectrics.

Enhancing Thermoelectric and Mechanical Properties of p-Type (Bi, Sb)2Te3 through Rickardite Mineral (Cu2.9Te2) Incorporation

“…The best BST-3 sample would be x = 0.00075 with zT ave of 1.06 and 70.89 H v for cross-plane and zT ave of 1.21 and 85.99 H v for in-plane direction. These values are slightly higher than those reported for BST-3/Cu 2 Te with zT ave ∼ 1.12 . The commercial BST (BST-ZM-com.)…”

“…48 Alloying Bi 0.3 Sb 1.7 Te 3 with Cu 2 Te optimized the hole concentration through both Cu substitution and formation of intrinsic defects, which also contributed to lower the lattice thermal conductivity due to enhanced point defect scattering. 44 However, most of the alloys reported so far in literature do not show concomitantly enhanced mechanical properties and high average zT values.…”

“…The lattice parameter calculations indicate a slight decrease in the a value and a marginal increase in the c value for both BST-5 and BST-3 samples upon doping with Cu 2.9 Te 2 , as shown in Figure S1. Previous studies have observed that in the crystal structure of BST, Cu can either substitute on the Bi/Sb site, 5,42,44,47,52,53 or be intercalated in the van der Waals gaps located between quintuple layers. 54 If Cu is intercalated, then the c parameter should increase with the increase in Cu content.…”

“…With recent studies introducing a second phase to the (Bi, Sb) 2 Te 3 matrix through alloying or doping, peak zT values could be shifted toward higher temperatures. − Besides enhanced thermoelectric properties, incorporating a phase with high mechanical strength, such as SiC or MgB 2 , into the matrix improved the mechanical properties of Bi 2 (Te, Se) 3 , and (Bi, Sb) 2 Te 3 . Moreover, doping (Bi, Sb) 2 Te 3 with Ag, Pb, Cu, or Cd increased the hole concentration, thereby hindering the bipolar effect, but at the expense of reduced carrier mobility. ,− , Among these elements, several studies were focused on Cu through direct doping or by adding a binary Cu-rich alloy.…”

“…Meanwhile, the formation of Cu 7 Te 5 (rickardite phase, described by another composition) as a secondary phase and localized Te-deficient regions were shown to act as hierarchical phonon scattering sources, yielding a substantial decrease in the lattice thermal conductivity . Alloying Bi 0.3 Sb 1.7 Te 3 with Cu 2 Te optimized the hole concentration through both Cu substitution and formation of intrinsic defects, which also contributed to lower the lattice thermal conductivity due to enhanced point defect scattering . However, most of the alloys reported so far in literature do not show concomitantly enhanced mechanical properties and high average zT values.…”