The Origin of Ultralow Thermal Conductivity in InTe: Lone‐Pair‐Induced Anharmonic Rattling

Abstract

Understanding the origin of intrinsically low thermal conductivity is fundamentally important to the development of high-performance thermoelectric materials, which can convert waste-heat into electricity. Herein, we report an ultralow lattice thermal conductivity (ca. 0.4 W m(-1) K(-1) ) in mixed valent InTe (that is, In(+) In(3+) Te2 ), which exhibits an intrinsic bonding asymmetry with coexistent covalent and ionic substructures. The phonon dispersion of InTe exhibits, along with low-energy flat branches, weak instabilities associated with the rattling vibrations of In(+) atoms along the columnar ionic substructure. These weakly unstable phonons originate from the 5s(2) lone pair of the In(+) atom and are strongly anharmonic, which scatter the heat-carrying acoustic phonons through strong anharmonic phonon-phonon interactions, as evident in anomalously high mode Grüneisen parameters. A maximum thermoelectric figure of merit (z T) of about 0.9 is achieved at 600 K for the 0.3 mol % In-deficient sample, making InTe a promising material for mid-temperature thermoelectric applications.

Synergistic Regulation of Phonon and Electronic Properties to Improve the Thermoelectric Performance of Chalcogenide CuIn1−xGaxTe2:yInTe (x = 0–0.3) with In Situ Formed Nanoscale Phase InTe

“…The size of the nano strips is 25-30 nm in width and 50-200 nm in length, and the domains ≈30 nm. [48] That is why we have observed the reduced lattice part κ L with InTe content increasing below 725 K. The schematic diagram is presented in Figure 6g for better understanding the transports of phonons and electrons. Figure 6f is the magnified image of Figure 6e, where two phases CuIn 1−x Ga x Te 2 and InTe are presented.…”

“…In order to confirm this assumption, we present the Pisarenko plot of the sample CuIn 1−x Ga x Te 2 :yInTe (x = 0.3) using the single parabolic band (SPB) model by taking an effective mass m *0 = 2.7 m o in Figure 5a, where the data circled in a wine dotted line is related to the pristine CuInTe 2 that mostly obeys the Pisarenko relation (SPB model) from different experiments [1,9,31,36,40,41,47] for comparison. This appearance suggests that the thermal conduction at low and middle temperatures is not only affected by the low thermal conductivity of InTe itself (κ L = ≈0.70 and 0.47 W m −1 K −1 at 319 and 605 K), [48] but also by the extra phonon scattering on the increased boundaries between InTe and CuIn 1−x Ga x Te 2 . In comparison, the α values of the present composites CuIn 1−x Ga x Te 2 :yInTe (x = 0, 0.1, 0.2) (hollow symbols circled by shaded area) are much close to the Pisarenko line for the corresponding n H values.…”

Enhancement in thermoelectric performance of n-type Pb-deficit Pb-Sb-Te alloys

“…In the case of pristine compositions, the highest value of zT obtained at 623 K was only 0.5 for Pb0.9Sb0.1Te, which then reaches to a maximum of 0.6 at 723 K. The better TE performance of Pb-deficit samples is due to their better electrical conductivity and lower thermal conductivity when compared to pristine Pb1-xSbxTe [28]. This reduction in  for self-deficient samples is expected to arise from phonon-scattering at the vacancies, which act as point-defects [37] and suppresses the lattice contribution by about 50%, when compared with pristine Pb1-xSbxTe [28]. A high temperature extrapolation of the linear temperature dependence zT plot of Pb-deficit composition containing 4 mol% Sb indicates a possible figure of merit of 1.3 at 850 K, making them a serious candidate for high temperature TE applications.…”

Phonon-glass electron-crystal behaviour by A site disorder in n-type thermoelectric oxides

“…9,10 Recently, ultralow thermal conductivities of 0.4-0.5 Wm -1 K -1 resulting from bonding anharmonicity where weakly bound cations act as rattlers were observed in metal tellurides. 11,12 As part of the search for materials based on less toxic and/or scarce components 13,14 that can operate under more demanding conditions including the broad temperature ranges required for some applications (automotive exhaust waste heat recovery: 350-700 K, industrial furnace waste heat recovery: 700-1100 K), 15,16 there is growing interest in thermoelectric oxides. 17,18 However, the strategies used to design high-performance thermoelectric materials based on small band gap, broad-band semiconductors and intermetallics cannot be translated directly to oxide materials.…”