Effects of Bi Alloying on the Thermoelectric Properties of p‐Type Mg₃Sb_2‐xBi_x Solid Solutions

Abstract

Bismuth is the most common alloying element for high-performance Mg 3 Sb 2 -based thermoelectric compounds. However, the electrical and thermal transport data is lacking for undoped Mg 3 (Sb, Bi) 2 solid solutions. In this study, theoretical calculation results show that Bi alloying can reduce the band gap of Mg 3 Sb 2 , favoring the regulation of carrier concentration. Both Mg 3 Sb 2 and Mg 3 SbBi compounds present a single band structure on the valence band maximum at Γ of the Brillouin zone. Incorporating the Bi element can slightly increase the density of states (DOS) on the valence band maximum, which is beneficial for the Seebeck coefficient. Mg 3 Sb 2-x Bi x (0 � x � 0.8) compounds were experimentally prepared via ball milling (BM) combined with the spark plasma sintering (SPS) technique. The carrier concentration, electrical conductivity, and power factor of the samples tend to increase with the increasing Bi content. Bismuth alloying significantly reduces the total thermal conductivity in the low-temperature range, with the lowest value of 0.65 Wm À 1 K À 1 obtained at ~400 K for the x = 0.2 sample. The peak ZT value of 0.077 at 800 K and the average ZT of 0.051 in the temperature range of 450-800 K are obtained for the x = 0.2 sample, which is 93% and 219% higher than those of the unalloyed sample, respectively. This work reveals the Bi-alloying induced transport mechanism and provides fundamental thermoelectric data regarding the undoped Mg 3 Sb 2-x Bi x (0 � x � 0.8) solid solutions.

Topological Electronic Transition Contributing to Improved Thermoelectric Performance in p‐Type Mg3Sb2−xBix Solid Solutions

“…Figure summarizes the power factor of p‐type Mg 3 Sb 2− x Bi x as a function of Bi content. For the p‐type Mg 3 Sb 2− x Bi x films in this work and bulks in literature reports, [ 41,42,63,65–69 ] the PF RT first increases and then decreases with the x value, see Figure 6a. The result points to an optimal composition of Mg 3 Sb 0.5 Bi 1.5 among the p‐type Mg 3 Sb 2− x Bi x films and bulks.…”

Visible-Light-Driven Denitrogenative C–C Bond Formation and Oxidative Difunctionalization of Vinyl Azides

“…The mechanism of the formation of α-oxyalkyl ketone derivatives has been explained based on the control experiments and literature survey. 52 53 54 55 So, the observed reactivity and the above investigations collectively point to a plausible mechanistic pathway shown in Scheme 6 . At first, in the presence of blue LED irradiation, RB is excited from the ground state to the excited state RB*.…”

“…As a result of homolysis, two radical species are formed simultaneously: hydroxyl radical (HO • ) and tert -butoxy radical ( t -BuO • ). 52 53 There might be another possible pathway of energy transfer of RB* to the ground-state triplet oxygen ( 3 O 2 ) and convert it into the singlet oxygen ( 1 O 2 ). This possible pathway might be excluded based on the result of the control experiment (Scheme 5c ), where DABCO is known as a singlet oxygen ( 1 O 2 ) quencher.…”

Graphene-assisted synergistic electronic DOS modulation and phonon scattering to improve the thermoelectric performance of Mg3Sb2-based materials

“…And thus, τ tot −1 ( x = 0) = 9.80 × 10 8 + 1.15 × 10 −40 ω 4 + 7.27 × 10 −16 ω 2 = C (unit in s −1 ) is obtained based on eqn (3) and eqn (3)–(5) with a Debye temperature θ D of 215 K, 45 a Grüneisen parameter γ of 1.81, 46 an average sound velocity v s of 2155 m s −1 (ref. 47) as well as an experimental κ L value of 1.17 W m −1 K −1 at RT for the x = 0 sample. Subsequently, we use the density of graphene of 2.20 × 10 3 kg m −3 , 48 the density of matrix of 4.40 × 10 3 kg m −3 , the number density of graphene V NP with different values (see Table S6 in the ESI†) and room-temperature lattice thermal conductivities for different samples to calculate the equivalent size R of G. In a sense, the R values derived from different samples should be equal.…”