Dramatically reduced lattice thermal conductivity of Mg2Si thermoelectric material from nanotwinning

Abstract

Dramatically reduced lattice thermal conductivity of Mg 2 Si thermoelectric material from nanotwinning, Acta Materialia, https://doi. Abstract:Tuning phonon transport to reduce the lattice thermal conductivity (κ L ) is crucial for advancing thermoelectrics (TEs). Traditional strategies on κ L reduction focus on introducing scattering sources such as point defects, dislocations, and grain boundaries, that may degrade the electrical conductivity and Seebeck coefficient. We suggest here, a novel twin boundary (TB) strategy that can decrease the κ L of Mg 2 Si by ~90%, but which may not degrade the electrical properties significantly. We validate this suggestion using density functional theory (DFT). We attribute the mechanism of TB induced κ L reduction to (i) the lower phonon velocities and larger Grüneisen parameter, (ii) "rattling" of the Mg−Mg pair induced soft acoustic and optical modes, (iii) shorter phonon lifetime and higher phonon scattering rate. We predict that the size of nanotwinned structure should be controlled between 3 nm and 100 nm in the Mg 2 Si matrix for the most effective κ L reduction. These results should be applicable for other TE or non TE energy materials with desired low thermal conductivity, suggesting rational designs of high-performance Mg 2 Si TE materials with low κ L for the energy conversion applications. Functional Theory 0.4 W m −1 K −1 and a zT of 1.5 at 1000 K [21]. In SnSe single crystals, The lattice anharmonicity leads to an exceptionally low κ L of 0.23 ± 0.03 W m −1 K −1 and an unprecedented zT of 2.6 ± 0.03 at 923 K [22,23]. In such TE materials as MgAgSb [24], Ag 5-δ Te 3 [25], and Ag 8 SnSe 6 [26], the complex crystal structure or weak chemical bonds leads to low heat capacity or low speed of sound, well explaining the low intrinsic κ L of < 0.5 W m −1 K [24-26]. Introducing phonon scattering sources such as point defects [27-29], dislocations [30-32], grain boundaries [33-35], can effectively shorten phonon relaxation time, giving rise to reduction in κ L . Multiple fillers inCoSb 3 can achieve broad-frequency phonon scattering, reducing κ L to the glass limit value of 0.2 W m −1 K −1 , and leading to an extremely high zT of 1.7 at 850 K [29]. Full-spectrum phonon scattering, which was achieved through grain boundary, dense dislocation arrays, and point defect,

Facile Fabrication of N-Type Flexible CoSb3-xTex Skutterudite/PEDOT:PSS Hybrid Thermoelectric Films

“…The efficiency of TE materials is described by a dimensionless figure of merit ZT = S 2 σTκ −1 , where S represents the Seebeck coefficient, σ represents electrical conductivity, κ represents thermal conductivity, and T represents absolute temperature. To improve the figure of merit, the majority of recent research is focused on two aspects: the enhancement of the power factor ( S 2 σ ) [ 11 , 12 , 13 , 14 , 15 , 16 , 17 ] and the reduction in thermal conductivity κ [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 ].…”

Thermoelectric performances for both p- and n-type GeSe

“…Because the Seebeck coefficient, electrical conductivity and electronic thermal conductivity are related to the electronic structure and carrier concentration, it is difficult to adjust and control a certain parameter alone to improve the thermoelectric properties of the material. In recent years, the efforts to enhance the ZT value mainly focus on improving the power factor through energy band engineering and reducing the thermal conductivity through nanometre or superlattice [ 1 – 6 ]. Both theoretical and experimental research shows that these methods can effectively improve ZT value, but it is difficult to be applied for the difficulty in preparation.…”

“…material. In recent years, the efforts to enhance the ZT value mainly focus on improving the power factor through energy band engineering and reducing the thermal conductivity through nanometre or superlattice [1][2][3][4][5][6]. Both theoretical and experimental research shows that these methods can effectively improve ZT value, but it is difficult to be applied for the difficulty in preparation.…”

Thermal resistance at a twist boundary and a semicoherent heterointerface

“…In this particular experiment, a Si thin film was bonded to a Si substrate at varying twist angles. TEM images revealed a nanometer-thick disordered region at the boundary, which contributes additional thermal resistance [18,42,43]. A detailed modeling of these contributions is necessary to understand the experimental results.…”