Electronic Band Structure Engineering and Enhanced Thermoelectric Transport Properties in Pb-Doped BiCuOS Oxysulfide

Abstract

In this paper, Bi 1−x Pb x CuOS samples (0 ≤ x ≤ 0.05) have been synthesized with a simple and scalable ballmilling process, followed by a reactive Spark Plasma Sintering. Our results highlight that, Pb for Bi substitution increases the charge carriers concentration by more than 2 orders of magnitude from 1.4 × 10 17 cm −3 to 2.6 × 10 19 cm −3 for x = 0 and x = 0.05, respectively. As a result, the electrical resistivity is divided by more than 50 at room temperature and the Seebeck coefficient drops from 707 μV K −1 to 265 μV K −1 where our experimental results are supported with density functional theory (DFT) calculations. Electronic structure calculations show that, just below the top of the valence band, several other bands are present and may contribute to the transport properties with appropriate tuning of the heavy-light valence band and the position of the Fermi level. Pb doping increases the number of holes pockets and several band degeneracies appear around the Fermi level, leading to a drastic enhancement of the power factor up to 0.2 mW m −1 K −2 at 700 K. This is 5 times higher than the value of the pristine compound. The intrinsically low thermal conductivity of 0.7 W m −1 K −1 at 700 K is interpreted on the basis of vibrational properties calculations within the Density Functional Perturbation Theory (DFPT) approach. It indicates that soft acoustic modes along the Γ−Z direction suggest weak interatomic bonding between the layers and possible strong anharmonicity. The power factor being enhanced with a minimal impact on the thermal conductivity, the figure of merit ZT reaches 0.2 at 700 K for x = 0.05. To the best of our knowledge, it is considered the best reported value among the family of oxysulfides

XBi4S7 (X = Mn, Fe): New Cost‐Efficient Layered n‐Type Thermoelectric Sulfides with Ultralow Thermal Conductivity

“…Grüneisen parameter and a low Young's modulus often lead to a low thermal conductivity. [71] AgSbTe2 (1727 m s −1 ), [64] BiSbSe3 (1629 m s -1 ), [73] Bi2Se3 (2083 m s −1 ), [74] and BiCuOS/Se (2126/2107 m s −1 ) [69,75] which have low thermal conductivity. Furthermore, the Young's moduli are close to 39.9 GPa and 28.5 GPa for MnBi4S7…”

Aqueous‐Based Low‐Temperature Synthesis and Thin‐Film Properties of Oxysulfide BiCuOS Nanoparticles

“…Obtaining solution of Bi 3 + and Cu + in basic pH was therefore necessary prior to react with the sodium sulfide solution. According to its potential-pH diagram, the stable form of bismuth species in water in the pH range [3][4][5][6][7][8][9][10][11][12][13] is the solid Bi(OH) 3 [23] and is therefore not soluble. Tartrate anions are known to form stable complexes with various cations.…”

“…[5,6] In particular, the presence of Cu + vacancies, observed in the refinement of synchrotron and neutron diffraction data, [7,8] is believed to be responsible for its p-type conductivity. [9,10] Moreover, its stability against air and water oxidation at room temperature as well as its composition made of non-toxic, cheap elements, makes BiCuOS a good alternative compared to other currently commercialized materials such as CIGS.…”

Electronic structure of a thermoelectric material: BiCuSO

“….) [5][6][7][8][9][10][11], the TE performance of BiCuChO (Ch = S, Se) can be dramatically enhanced while the lattice structure is barely influenced, which suggests the excellent TE performance in BiCuChO is likely rooted in their electronic structures, as is also supported by first-principles calculation [8,12]. On the other hand, BiCuSO has attracted research interest due to its potential for hosting unconventional superconductivity [13][14][15][16][17][18]: Ubaldini et al reported a superconducting transition at 5.8 K in polycrystalline BiCu 0.9 SO [13], and Mazin and coworkers proposed that the superconductivity in BiCu 0.9 SO may be mediated by spin fluctuation induced by Cu deficiency [14,16], despite the controversial experimental observation of semiconductorlike behavior in subsequent transport measurements [17][18][19][20][21][22][23].…”