Unravelling p–n Conduction Transition in High Thermoelectric Figure of Merit Gallium-Doped Bi₂Te₃ via Phase Diagram Engineering

Abstract

We revisit the well-established Bi2Te3 via phase diagram engineering. Along with a phase diagram in hand, it is realized that the solubility of Ga in Bi2Te3 is coincident with the p–n transition zone in Ga–Bi2Te3 alloys. The best-performing n-type (Bi2Te3)0.93(Ga2Te5)0.07 possesses a peak zT ∼ 1.5 at 300 K, which is attributed to the reduced κ ∼ 1.8 W m–1 K–1 and the low-lying ρ. The p-type Bi1.99Ga0.01Te3 also exhibits a peak zT of 1.2 at 300 K. In other words, the addition of Ga leads to high-zT p-type or n-type bismuth-tellurides, which simplifies the conventional synthesis route that usually involves different dopants.

Leveraging Deep Levels in Narrow Bandgap Bi0.5Sb1.5Te3 for Record‐High zTave Near Room Temperature

“…This is a recordhigh zT ave value reported for the p-type (Bi,Sb) 2 Te 3 material in view of both the thermal and electrical properties measured along the same direction (Figure 6f). [5,22,44,45,[47][48][49][50][51][52] One must measure all the TE properties and calculate the zT in the same direction to avoid over-estimation of zT. Otherwise, a zT value ≈ 2.0 would be obtained if the in-plane PF and the out-of-plane κ are used for the w = 0.004 sample (cf.…”

Eliciting High‐Performance Thermoelectric Materials via Phase Diagram Engineering: A Review

“…Both the κ(T ) and κ L (T ) curves drop with increasing x and y, attributing to the alloying effect that leads to the enhanced phonon scattering. As a result, the (Bi 2 Te 3 ) 0.09 (Cu 2 Te) 0.01 and the Bi 1.99 Cu 0.01 Te achieve the highest peak values of 1.2-1.3 at 300 K. Although the n-type x ¼ 0.09 only attains the peak zT % 1.0 at 300 K, the temperature-independent zT curve [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][35][36][37][38][39][40][41] The corresponding synthesis method and nominal composition are also shown later. Reproduced (Adapted) with permission.…”

“…[69] Moreover, at least four ternary compounds, the Ge A very similar case has later been found in the Ga-Bi 2 Te 3 . [24] The isothermal section of the ternary Bi-Ga-Te system at 523 K (Figure 3a) suggests that the solubility in Bi 2 Te 3 is less than 1 at% Ga. Unlike the isothermal section of Bi-Te-Ge (Figure 2a), the Bi-Ga-Te system contains no ternary compounds at 523 K. The thermally equilibrated microstructures (Figure 3b and 3c) further confirm the existence of three-phase Bi 2 Te 3 þ Bi 4 Te 5 þ Ga 2 Te 3 and Bi 2 Te þ Bi 4 Te 3 þ Ga 2 Te 3 region.…”

“…In line with the thermodynamic approach, the phase boundary mapping [22] and the phase diagram engineering [23][24][25][26][27][28][29][30] both make great use of the equilibrium phase diagrams, while the latter emphasizes the homogeneity regions and the phase transformations. It shall be noted that the phase boundary mapping has been exploited to the n-type Mg 3 Sb 2 , [31][32][33][34] which yields the enhanced TE performance within an optimal compositional region.…”

“…e) Magnified isothermal section superimposed with color contour of Seebeck (S) coefficient measured at 300 K. The temperature-dependent f ) zT values, g) electrical resistivity (ρ(T )) curves, h) Seebeck coefficient (S(T )) curves, i) thermal conductivity (κ(T )) curves, and j) lattice thermal conductivity (κ L (T )) curves of Bi-Ge-Te alloys. Adapted with permission [24]. Copyright 2020, American Chemical Society.…”