Entropy optimized phase transitions and improved thermoelectric performance in n-type liquid-like Ag9GaSe6 materials

165

120

Thermoelectric technology has attracted great attention due to its ability to recover and convert waste heat into readily available electric energy. Among the various candidate materials, liquid‐like compounds have received tremendous research interest on account of their intrinsically ultralow lattice thermal conductivity, tunable electrical properties, and high thermoelectric performance. Despite their complex phase transitions and diverse crystal structures, liquid‐like materials have two independent sublattices in common: one rigid sublattice formed by immobile ions for the free transport of electrons and one liquid‐like sublattice consisting of highly mobile ions to interrupt the thermal transports. This review first outlines the common structural features of liquid‐like thermoelectrics, along with their unusual electron and phonon transport behaviors that well satisfy the concept of “phonon‐liquid electron‐crystal.” Next, some commonly adopted strategies for further improving their thermoelectric performance are highlighted. The main progress achieved in the typical liquid‐like TE materials is then summarized, with an emphasis on their diverse crystal structures, common characteristics, and unique transport properties. The recent understandings on the stability issue of liquid‐like TE materials are also introduced. Finally, an outlook is given for the liquid‐like materials with the aim to boost further development in this exciting scientific subfield.

Section: Strategies For Improving Te Performance Beyond Plec Conceptsupporting

confidence: 76%

Recent Advances in Liquid‐Like Thermoelectric Materials

Zhao

Qiu

Shi

et al. 2019

165

120

“…With the continuous increase of the global energy consumption, more clean and renewable energy solutions are needed. Thermoelectric (TE) materials are capable of converting waste heat straightly into electricity without mechanical devices, which helps to promote the utilization of energy for the sustainable development . The conversion efficiency of TE materials is determined by the dimensionless figure‐of‐merit ZT = σS 2 T /κ, where σ is the electrical conductivity, S is the Seebeck coefficient, T is the absolute temperature, and κ is the thermal conductivity.…”

Section: Introductionmentioning

confidence: 99%

High‐Performance N‐type Mg₃Sb₂ towards Thermoelectric Application near Room Temperature

Zhang

Chen

Yao

et al. 2019

Se-doped Mg 3.2 Sb 1.5 Bi 0.5 -based thermoelectric materials are revisited in this study. An increased ZT value ≈1.4 at about 723 K is obtained in Mg 3.2 Sb 1.5 Bi 0.49 Se 0.01 with optimized carrier concentration ≈1.9 × 10 19 cm −3 . Based on this composition, Co and Mn are incorporated for the manipulation of the carrier scattering mechanism, which are beneficial to the dramatically enhanced electrical conductivity and power factor around room temperature range. Combined with the lowered lattice thermal conductivity due to the introduction of effective phonon scattering centers in Se&Mn-codoped sample, a highest room temperature ZT value ≈0.63 and a peak ZT value ≈1.70 at 623 K are achieved for Mg 3.15 Mn 0.05 Sb 1.5 Bi 0.49 Se 0.01 , leading to a high average ZT ≈1.33 from 323 to 673 K. In particular, a remarkable average ZT ≈1.18 between the temperature of 323 and 523 K is achieved, suggesting the competitive substitution for the commercialized n-type Bi 2 Te 3 -based thermoelectric materials.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201906143. helps to promote the utilization of energy for the sustainable development. [1][2][3][4][5][6][7] The conversion efficiency of TE materials is determined by the dimensionless figureof-merit ZT = σS 2 T/κ, where σ is the electrical conductivity, S is the Seebeck coefficient, T is the absolute temperature, and κ is the thermal conductivity. High TE performance needs high electrical conductivity, high Seebeck coefficient, and low thermal conductivity. However, it is hard to independently optimize them because they are interconnected. [8][9][10][11][12][13][14] Zintl compounds have complex crystal structure desired for high TE performance. [15,16] The anions provide the "electron-crystal" structure through the covalent bonding network, and Zintl cations play the role of the "phonon scattering center" for extremely low lattice thermal conductivity. [5,[17][18][19] Most of Zintl phases are intrinsically p-type and difficult to be doped to n-type semiconductors. While Mg 3 Sb 2 -based Zintl-phase materials show outstanding n-type TE performance by chalcogens or rare earth doping. [20][21][22] The maximum peak ZT value of Te-doped Mg 3+δ Sb 1.5 Bi 0.5 is higher than ≈1.5 at 723 K. [21][22][23][24][25][26] Especially, a prominent average ZT value has recently been obtained at around room temperature range, which is close to that of the commercialized Bi 2 Te 3 -based TE material. Considering the scarcity of Te, Mg 3 Sb 2 -based materials are more promising for large-scale applications. The high performance at lower temperature is considered the results of the enhanced carrier mobility, which is ascribed to the Sb/Bi alloying for band structure tailoring [27][28][29] and transition metal doping (Nb, Ta, Co, Mn, Hf, etc.) or grain size increment for scattering mechanism manipulation. [24,25,[30][31][32][33][34] The average ZT ≈ 1.05 was obtained for Mn&Te-codoped Mg 3+δ Sb 1.5 Bi 0.5[35] and ≈1.08 was obt...

“…The identical tendency of absolute Seebeck coefficients ( S ) for all Ag 8 Sn(S 1− x Se x ) 6 ( x = 0.00, 0.01, 0.03, 0.05, 0.10) compounds is depicted in Figure 6e, first quickly decrease below phase transition temperature range, then slightly decrease above phase transition temperature range, which is attributed to the increased effective mass after phase transition in the cubic phase of Ag 8 Sn(S 1− x Se x ) 6 compounds. [ 24,27 ] Meanwhile, the absolute Seebeck coefficients of all compounds slightly decrease with increasing Se contents, opposite to the variation trend of electrical conductivities as expected.…”

Section: Resultsmentioning

confidence: 56%

“…Recently, a class of “liquid‐like” TE materials with complex phase transitions, ultralow lattice thermal conductivity, and liquid‐like ionic conduction have been reported, Cu 2− x (S, Se, Te), [ 19–21 ] Ag 2 (S, Se, Te), [ 22,23 ] argyrodite, [ 24–36 ] AgCrSe 2 , [ 37,38 ] CuAgSe, [ 39 ] and AgCuTe [ 40 ] to name a few. Argyrodites are good examples of liquid‐like TE materials.…”

Section: Introductionmentioning

confidence: 99%

“…Regarding the high‐temperature TE properties of argyrodites, most prior studies are focused on selenides and tellurides, leaving sulfides conspicuously less heeded ( Figure ). [ 24–36 ] It is therefore imperative to study high‐temperature TE properties of sulfides argyrodites to fill this knowledge gap toward a holistic comprehension of the rich materials physics and materials chemistry behaviors of 816 phase argyrodites. Generally speaking, a material with high crystal lattice symmetry possess high band degeneracy and large density of states effective mass

m_{d}^{*}

m_{d}^{*} = N_{V}^{2 / 3} m_{b}^{*}

, where N V refers to both orbital and symmetry related degeneracy and

m_{b}^{*}

is the band effective mass.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

High Thermoelectric Performance in Sulfide‐Type Argyrodites Compound Ag₈Sn(S₁₋_xSe_x)₆ Enabled by Ultralow Lattice Thermal Conductivity and Extended Cubic Phase Regime

Shen

Xia

Yang

et al. 2020

Argyrodites with a general chemical formula of A 8 BC 6 are known for complex phase transitions, ultralow lattice thermal conductivity, and mixed electronic and ionic conduction. The coexistence of ionic conduction and promising thermoelectric performance have recently been reported in selenide and telluride argyrodites, but scarcely in sulfide argyrodites. Here, the thermoelectric properties of Ag 8 Sn(S 1−x Se x ) 6 are reported. Specifically, Ag 8 SnS 6 exhibits intrinsically ultralow lattice thermal conductivities of 0.61-0.31 W m −1 K −1 over the whole temperature range from 32 to 773 K due to distorted local crystal structure, relatively weak chemical bonding, rattler-like Ag atoms, low-lying optical modes, and dynamic disorder of Ag ions at high temperatures. Se doping shifts the orthorhombic-cubic phase transition from 457 K at x = 0 to 430 K at x = 0.10, thereby expanding the temperature range of the thermoelectrically favored cubic phase. A figure of merit zT value ≈ 0.80 is achieved at 773 K in Ag 8 Sn(S 1−x Se x ) 6 (x = 0.03), the highest zT value reported in sulfide argyrodites. These results fill a knowledge gap of the thermoelectric study of argyrodites and contribute to a comprehensive understanding of the chemical bonding, lattice dynamics, and thermal transport of argyrodites.a potential for practical applications. Yet, it is still a challenge to decouple the adversely correlated {σ, S, κ e } toward high zT values via electronic and phonon band engineering. [3][4][5][6][7][8] Many efforts have been devoted to discover novel TE materials such as cage-like filled skutterudites (e.g., CeFe 4 Sb 12 , CoSb 3 , Sr 8 Ga 16 Ge 30 , etc.), [9][10][11][12] Zintl-phase compounds (e.g., CaZn 2 Sb 2 , Mg 3 Sb 2 , YbMg 2 Bi 2 , etc.), [13][14][15][16] and defective half-Heusler compounds (e.g., Nb 0.8 CoSb, Ti 0.9 NiSb, V 0.9 CoSb, etc.) [17] that possess a long-range order favoring charge carrier mobility while disordered in short range to inhibit heat-carrying phonons in the context of "phonon-glass-electron-crystal". [18] Recently, a class of "liquid-like" TE materials with complex phase transitions, ultralow lattice thermal conductivity, and liquidlike ionic conduction have been reported, Cu 2−x (S, Se, Te), [19][20][21] Ag 2 (S, Se, Te), [22,23] argyrodite, [24][25][26][27][28][29][30][31][32][33][34][35][36] AgCrSe 2 , [37,38] CuAgSe, [39] and AgCuTe [40] to name a few. Argyrodites are good examples of liquid-like TE materials. Argyrodites include 716, 816, and 916 phases in chemistry, with a general chemical formula A 12−n