Synergistically optimizing electrical and thermal transport properties of Bi₂O₂Se ceramics by Te‐substitution

Abstract

Bi 2 O 2 Se oxyselenides, characterized with intrinsically low lattice thermal conductivity and large Seebeck coefficient, are potential n-type thermoelectric material in the mediate temperature range. Given the low carrier concentration of~1015 cm À3at 300 K, the intrinsically low electrical conductivity actually hinders further enhancement of their thermoelectric performance. In this work, the isovalent Tesubstitution of Se plays an effective role in narrowing the band gap, which notably increases the carrier concentration to~10 18 cm À3 at 300 K and the electron conduction activation energy has been lowered significantly from 0.33 to 0.14 eV. As a consequence, the power factor has been improved from K E Y W O R D Sdopants/doping, electrical conductivity, thermal conductivity, thermoelectric properties | INTRODUCTIONEver-increasingly severe energy and environment crisis is a global issue and thus exploration of clean and sustainable energy sources has become a worldwide consensus. Thermoelectrics, capable of directly and reversibly converting temperature difference into electricity without moving parts, is currently considered as a highly possible solution. Numerous efforts have been devoted to identifying novel thermoelectric materials as well as optimizing the thermoelectric performance of well-known ones. 1,2 The practical energy conversion efficiency is determined by the figure of merit, ZT = S 2 rT/j, where S, r, T and j represent the Seebeck coefficient, electrical conductivity, absolute temperature and the thermal conductivity, respectively. However, these properties defining the ZT value are strongly interrelated via the carrier concentration, making it quite challenging to obtain high thermoelectric performance. 3 Due to the low conversion efficiency, the application of thermoelectric devices is limited to niche market

Raman Spectra and Strain Effects in Bismuth Oxychalcogenides

“…In the crossed polarization configuration (θ=90°), the intensity of B1g mode gradually increases from zero (β =0°) to its maximal value for β =45°, whereas A1g mode vanishes in this configuration. So we could choose specified sample orientation (β=45°, x ' =1/ √2 [110], y ' =1/ √2 [1][2][3][4][5][6][7][8][9][10]) and various polarized scattering configuration to assign four different modes in the Bi2O2Se (Bi2O2Te) system (see Figure S3 (c)). This hypothesis could be verified by future polarized Raman scattering experiments when obtain a good sample.…”

“…This hypothesis could be verified by future polarized Raman scattering experiments when obtain a good sample. x ' =1/√2[110], y ' =1/√2 [1][2][3][4][5][6][7][8][9][10], z = [001]).…”

“…6 Actually, Bi2O2Se was initially studied in its bulk (ceramics) form as potential n-type thermoelectric material. [7][8][9][10] After Bi2O2Se was synthesized into ultrathin crystal films with a thickness between tens to two layers, 6,11 it was recognized as a superior semiconductor, e.g., field-effect transistors made from it exhibit a current on/off ratio larger than 10 6 at room temperature. 6 There exists a strong spin-orbit interaction in 2D Bi2O2Se sheets, 12 and they were shown to have excellent optoelectronic performance as photodetectors.…”

Boosting the thermoelectric performance of Bi2O2Se by isovalent doping

“…These studies concerning donor doping could evidently increase the electrical conductivity via carrier engineering, contributing to enhanced ZT values of Bi 2 O 2 Se. Recently, the formation of Bi 2 O 2 Se‐based solid solution with isostructural Bi 2 O 2 Te has been demonstrated to effectively tune the band structure . The narrowed band gap favors the excitation of electrons and consequently the enhancement of electrical conductivity and a new record ZT value of 0.28 at 823 K for Bi 2 O 2 Se 0.96 Te 0.04 has been achieved.…”

Electrical and Thermal Transport Properties of n‐type Bi6Cu2Se4O6 (2BiCuSeO + 2Bi2O2Se)

“…[25] Interestingly, due to Se vacancies, [26] Bi 2 O 2 Se could exhibit n-type conductive transports. [27] To fully functionalize the features of BiCuSeO and Bi 2 O 2 Se, a new series of Bi 6 Cu 2 Se 4 O 6 oxyselenides are synthesized with the 1:1 ratio of BiCuSeO and Bi 2 O 2 Se through a simple solidstate reaction method that followed the suggestions by Rosseinsky et al [28,29] We expect to realize the low thermal conductivities and n-type conducting transports in Bi 6 Cu 2 Se 4 O 6 via succeeding from the advances of BiCuSeO and Bi 2 O 2 Se, respectively. Indeed, we found the low thermal conductivity in Bi 6 Cu 2 Se 4 O 6 due to the strong interlayer phonon scattering and the complex layered structures.…”