Improvement of Thermoelectricity Through Magnetic Interactions in Layered Cr₂Ge₂Te₆

Abstract

The magnetism is proposed as a way to improve thermoelectricity, which may overcome the tradeoff between electrical conductivity and Seebeck coefficient. The correlation between magnetic configurations and thermoelectricity in layered magnetic semiconductor Cr2Ge2Te6 has been investigated using first‐principles calculations, combined with semi‐classical Boltzmann theory. The electronic structures and relevant transport properties for paramagnetic phase have been stimulated. Special quasi‐random structure (SQS) is employed to simulate electronic properties of paramagnetic state corresponding to spin‐disordered configurations. The temperature dependence of calculated Seebeck coefficient, electrical conductivity, and the figure of merit ZT is in good agreement with experimental values for paramagnetic phase. For p‐type Cr2Ge2Te6, the maximum ZT can reach 0.54 at 830 K and the carrier concentration a value of 2.1 × 1020 cm−3. The calculated figure of merit can further increase by 42% compared to the maximum experimental result by optimized doping level. Cr2Ge2Te6 without spin polarization shows a metal electric band structure, which deviates from the semiconductor of truth. This means that magnetic interactions play an important role in electronic structure and result in an excellent thermoelectricity of paramagnetic Cr2Ge2Te6. High band valley degeneracy, flat valence bands, and the localized partial density of states (PDOS) of magnetic atoms near Fermi surface induce a large Seebeck coefficient, meanwhile a good electrical conductivity is maintained in this magnetic semiconductor with high symmetry.

Polaronic Conductivity in Cr2Ge2Te6 Single Crystals

“…[ 1 ] The mechanism of intrinsic long‐range magnetic order in monolayers of 2D materials such as CrI 3 and bilayer Cr 2 Ge 2 Te 6 might be exploited for design of novel spin‐related devices. [ 2,3 ] They can be stacked into heterostructures [ 4–9 ] and their physical properties are highly tunable by carrier doping, [ 10–13 ] strain, [ 14–16 ] vacancies, [ 17–21 ] pressure, [ 22–26 ] and electric field. [ 27–30 ]…”

“…[1] The mechanism of intrinsic long-range magnetic order in monolayers of 2D materials such as CrI 3 and bilayer Cr 2 Ge 2 Te 6 might be exploited for design of novel spin-related devices. [2,3] They can be stacked into heterostructures [4][5][6][7][8][9] and their physical properties are highly tunable by carrier doping, [10][11][12][13] strain, [14][15][16] vacancies, [17][18][19][20][21] pressure, [22][23][24][25][26] and electric field. [27][28][29][30] Cr 2 Ge 2 Te 6 exhibits a paramagnetic (PM) to ferromagnetic (FM) transition with the Curie temperature (T c ) of ≈61-68 K in bulk, an out-of-plane easy axis and negligible coercivity.…”

Recent Progress in Multiphase Thermoelectric Materials

“…Examples of magnetic semiconductors are FeSb 2 [244,245], MnTe [246][247][248], Cr 2 Ge 2 Te 6 [249], MgAgSb [250], MnSe [251], and FeSe [252]. Experimental results have shown their potential as thermoelectric materials; for instance, a massive Seebeck coefficient of ~27 mV/K has been reported for FeSb 2 (albeit at a low temperature of ~12 K) [253].…”

Polaronic Conductivity in Cr$_2$Ge$_2$Te$_6$ Single Crystals

“…1 The mechanism of intrinsic longrange magnetic order in monolayers of 2D materials such as CrI 3 and bilayer Cr 2 Ge 2 Te 6 might be exploited for design of novel spin-related devices. 2,3 They can be stacked into heterostructures [4][5][6][7][8][9] and their physical properties are highly tunable by carrier doping, [10][11][12][13] strain, [14][15][16] vacancies, [17][18][19][20][21] pressure [22][23][24][25][26] and electric field. [27][28][29][30] Cr 2 Ge 2 Te 6 exhibits a paramagnetic (PM) to ferromagnetic (FM) transition with the Curie temperature (T c ) of 61 ∼ 68 K in bulk, an out-of-plane easy axis and negligible coercivity.…”