d-Orbital-Driven Low Lattice Thermal Conductivity in TiRhBi: A Root for Potential Thermoelectric and Microelectronic Performance

Self Cite

p-Type NbFeSb-based half-Heusler compounds possess good thermoelectric (TE) properties with the benefits of abundantly accessible constituent elements, a high Seebeck coefficient, and a large power factor (PF) but a relatively high κ l . Reducing the κ l is crucial to increase the figure of merit (zT). This is generally done with isovalent doping, alloying, nanostructuring, etc., but these adversely affect carrier mobility. We have performed transport calculations on NbFeSb and NbFeBi to see the same-group substitution effects on thermal conductivity. A usual way to study the phonon transport properties is to solve the Boltzmann transport equation (BTE) within the firstprinciples approach, which has proven experimental reproducibility. The doped or nanostructured system is computationally demanding with the above approach and appeals for more convenient access, such as the deformation potential (DP) method. We study the κ l of pristine NbFeSb and NbFeBi with the first-principles-based BTE and compare it with the DP model. Bi substitution at the Sb site in NbFeSb reduces the κ l (from 4.5 to 2 W/mK at 1000 K) without any complication of nanostructuring/doping and has the same high band degeneracy at the band edges. We also benchmark the DP model prediction so that further doping with aliovalent atoms can be studied with the DP model to obtain the high zT value.

Section: Results and Analysescontrasting

confidence: 99%

Section: Results and Analysesmentioning

confidence: 70%

Theoretical Study of Lattice Thermal Conductivity of NbFeM (M = Sb, Bi) for Potential Thermoelectric Performance

Keshri,

Paul,

Maurya

et al. 2023

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“…Another challenging issue for the improvement of ZT is the reduction of κ l . The strategies that are being applied for the suppression of the κ l are acoustic phonon scattering by point defects, , lattice softening, nanostructuring, , intrinsic lowering of κ l , , etc.…”

Section: Introductionmentioning

confidence: 99%

Computational Exploration of Ultralow Lattice Thermal Conductivity and High Figure of Merit in p-Type Bulk RbX₂Sb (X = K, Na)

Mandal

Sarkar

2023

Using density functional theory and the Boltzmann transport equation, we have herein studied the electronic structure and thermoelectric behavior of two bulk bialkali antimonides RbK2Sb and RbNa2Sb. Our calculation reveals that both the antimonides exhibit ultralow lattice thermal conductivities resulting from the intrinsic phonon scattering. The lattice thermal conductivities of RbK2Sb and RbNa2Sb at 700 K (300 K) are found to be 0.150 (0.350) and 0.228 (0.532) W m–1 K–1, respectively. Thermodynamically, mechanically, dynamically, and thermally stable p-type RbK2Sb proclaims high values of the Seebeck coefficient due to the large band effective masses and thus the DOS effective masses of the holes, while p-type RbNa2Sb exhibits a moderate Seebeck coefficient and optimum electrical conductivity due to the relatively lower band effective mass and the high relaxation time (corresponding to high mobility) of the holes. Estimated maximum values of the figure of merit at 700 K (300 K) are 4.40 (1.91) and 5.84 (2.76) for the p-type RbK2Sb and RbNa2Sb, respectively.

“…As T is increased, so does the entropy due to the enhanced number of microstates. In Figure b, we have compared the vibrational entropy of In 4 Te 3 with other low thermal conductive materials such as In 4 Se 3 (this work), TiCoBi, TiRhBi, Ti 2 CrGe, and Ti 0.75 HfMo 0.25 CrGe . Softer phonon modes, due to the antibonding or nonbonding nature of In4 in In 4 Te 3 , can easily be excited to higher states.…”

Section: Resultsmentioning

confidence: 99%

Antibonding or Nonbonding Interaction-Driven Phonon Modes Softening and Wave-like Interband Thermal Conduction in Layered In₄Te₃ under the Framework of Wigner Transport Formalism

Das,

Banerji

2023

In 4 Te 3 , a p-type analogue of n-type In 4 Se 3 , exhibits anomalous thermal conductivity (κ L ). The value of κ L is intrinsically very low, 0.7 W m −1 K −1 at 300 K, and it is weakly temperature (T)-dependent, which deviates from the conventional κ L ∝ T −1 variation. Thus, In 4 Te 3 finds its application as a thermoelectric material in the midtemperature range. Here, employing a completely ab initio-based DFT framework, three-phonon scattering process, and Wigner transport equation, we found that In 4 Te 3 exhibits strong anharmonicity in the acoustic region as well as the low energy optical region. The mean free path already reached the "Ioffe-Regel limit" in space even at a low T which is consistent with low κ L . The anharmonicity arises due to the antibonding and nonbonding overlap of In4 valence electrons with its neighbors. Such a weak bond formation capability of In4 has very low interatomic force constants, which results in overall low elastic properties, viz. sound velocity (1947.24 m s −1 ), Debye temperature (184 K), Young's modulus (51.56 GPa), etc., indicating considerable amount of lattice softening. Interestingly, those softened Einstein-like modes at ∼0.72 THz form overlapped phonon bands and promote their wave-like tunneling. Even at low T (50 K), the line-widths of the individual modes are still larger than their interband spacing, which lowers their particle-like propagation but enhances wave-like tunneling, eventually leading to the dual particle-wave behavior of the heat carrying phonons. At high T, the intrinsic phonon−phonon interaction dominates and the calculated three-phonon scattering time lies between the "Wigner" and "Ioffe-Regel limits" in time which manifests nonstandard wave-like thermal conductivity in the system.