Intrinsically Minimal Thermal Conductivity in CubicI−V−VI2Semiconductors

Abstract

We report measurements of the thermal conductivity of high-quality crystals of the cubic I-V-VI2 semiconductors AgSbTe2 and AgBiSe2. The thermal conductivity is temperature independent from 80 to 300 K at a value of approximately 0.70 W/mK. Heat conduction is dominated by the lattice term, which we show is limited by umklapp and normal phonon-phonon scattering processes to a value that corresponds to the minimum possible, where the phonon mean free path equals the interatomic distance. Minimum thermal conductivity in cubic I-V-VI2 semiconductors is due to an extreme anharmonicity of the lattice vibrational spectrum that gives rise to a high Grüneisen parameter and strong phonon-phonon interactions. Members of this family of compounds are therefore most promising for thermoelectric applications, particularly as p-type materials.

Low Sound Velocity Contributing to the High Thermoelectric Performance of Ag8SnSe6

“…One successful strategy for improving zT is to enhance the power factor S 2 / ρ through band engineering,2, 3, 4, 5, 6, 7 provided the carrier concentration is optimized 8. The other effective strategy is typified by minimizing the only one independent material property, the lattice thermal conductivity ( κ L ), through nanostructuring,9, 10, 11, 12, 13, 14, 15 liquid phonons,16, 17 and lattice anharmonicity 18, 19…”

Understanding the electronic and phonon transport properties of a thermoelectric material BiCuSeO: a first-principles study

“…Over the past five years, the ZT value of BiCuSeO has been continuously increased from 0.76 to 1.5 by doping to enhance the power factor as well as nanostructuring to further reduce the lattice thermal conductivity. Many experimental works on the transport properties of BiCuSeO indicate that the compound exhibit (1) a relatively larger Seebeck coefficient at optimized concentration (230 V / K  @873K [9], 243 V / K  @923K [10 ]), (2) [13]. Moreover, the low lattice thermal conductivity may originate from the interface phonon scattering and low-phonon-conductive heavy elements [4].…”

“…However, it is usually difficult to do so since the transport coefficients S ,  and e k are coupled with each other and related to the electronic band structure and carrier concentration. An effective way of searching good TE materials is to find materials with intrinsic low lattice thermal conductivity, such as CoSb 3 [1], AgSbTe 2 [2], and MgAgSb [3]. Recently, a new layered oxyselenide BiCuSeO with very small lattice thermal conductivity was proposed to be a potential TE material [4], and a large amount of efforts have been devoted to enhance its TE performance [5][6][7][8][9].…”

Phonon scattering rates and atomic ordering inAg1−xSb1+xTe2+x(Ma1, Delaire2, Specht3 et al. 2014Phys. Rev. B130120View full textAdd to dashboardCite

“…For example, in PbTe κ lat 2.2 Wm −1 K −1 at 300 K, further decreasing at higher temperatures owing to anharmonicity-dominated phonon scattering [6][7][8][9] . The compound AgSbTe 2 exhibits an even lower thermal conductivity, κ lat 0.7 Wm −1 K −1 at 300 K, also showing a glass-like temperature-independent behavior [10][11][12][13][14] . In pure form, this compound exhibits a relatively high ZT ≈ 1.2 at 720 K 3,15 .…”

“…10). Several mechanisms have been suggested to explain the very low, glass-like κ lat , such as strong anharmonicity 12,17 , force-constants differences around Ag and Sb atoms 18 , and nanoprecipitates 13,14,[19][20][21][22] . However, the lack of direct microscopic measurements of the phonon scattering rates and mean-free-paths has hampered a detailed understanding.…”