Beneficial Effect of Na₂CO₃ Additions on the Thermoelectric Performance of Melt‐Route Cu₂Se

Abstract

High‐performance thermoelectric materials require simultaneous reduction of thermal conductivity and electrical resistivity, among other criteria. Here it is shown that the introduction of Na2CO3 into the melt‐route fabrication process for the well‐known thermoelectric Cu2Se has a beneficial and surprisingly strong effect. There is a significant enhancement in electrical conductivity which density functional theory calculations suggest may be due to the effect of Na and O doping in the Cu2Se matrix. There is also a 34% reduction in thermal conductivity which is likely due to a high density of defects causing scattering of phonons. Overall, however, there is only relatively a small change in Seebeck coefficient. A higher power factor of 12.6 µW cm−1 K−2 is achieved versus 8.8 µW cm−1 K−2 for standard Cu2Se. A very high value of zT of 2.3 is obtained at 804 K versus 1.1 for standard Cu2Se.

Interface‐Enhanced High‐Temperature Thermoelectricity in Cu1.99Se/B4C Composites with Synergistically Improved Mechanical Strength

“…a) Total thermal conductivity, b) Electronic thermal conductivity, c) Lattice thermal conductivity, d) Longitudinal and transverse wave sound velocity at room temperature, e) Average sound velocity and phonon mean free path at room temperature, f) Lattice thermal conductivity calibrated by Effective Medium Theory (EMT), g) Normalized phonon density of states (PDoS) of B 4 C and Cu 2 Se derived from earlier studies, [ 50,51 ] h) ZT values and i) Comparison of the maximum ZT value in this work with the highest value reported in previous studies. [ 14–17,19,46,47,53–62 ]…”

“…Besides, the normalized phonon density of states (PDoS) of Cu 2 Se and B 4 C only [50,51] h) ZT values and i) Comparison of the maximum ZT value in this work with the highest value reported in previous studies. [14][15][16][17]19,46,47,[53][54][55][56][57][58][59][60][61][62] shows minimal overlaps (Figure 4g), [50,51] indicating huge interfacial thermal resistance at higher frequencies. This dramatically low 𝜅 l could be also related to the weak electron-phonon coupling induced by nano-sized secondary phases, as reported by Wu et al [52] Consequently, by incorporating 0.9 vol.% B 4 C into the Cu 1.99 Se matrix, a high PF can be achieved without sacrificing too much 𝜅, resulting in a maximum ZT of 2.6 at 1025 K (Figure 4h), supported by the good repeatability and reproducibility of our experimental results (Figures S18,S19, Supporting Information).…”

“…Figure 4i displays the comparison of the peak ZT in our work with the highest value reported in most previous publications. [14][15][16][17]19,46,47,[53][54][55][56][57][58][59][60][61][62] It is obvious that the maximum ZT in this paper ranks at the leading level, which is very competitive among Cu 2 Se-based composites.…”

Fine-Tuning Bi2Te3-Copper Selenide Alloys Enables an Efficient n-Type Thermoelectric Conversion

“…It was revealed that the β-phase of Cu 2−x Se exhibits the ideal phonon-glass electron-crystal model, and is also relatively economical and eco-friendly [ 25 , 26 , 27 , 28 ]. More importantly, the very high ZT value, up to 2.3~2.7, of Cu 2 Se-based materials was demonstrated as a characteristic of the p-type TE, due to the optimal carrier concentration and intensive phonon scattering [ 29 , 30 ]. Some researchers have revealed that alloying with Se or some metallic cations can easily affect the conduction band structure, which is effective to tune the carrier concentration and transport property [ 23 , 31 , 32 , 33 , 34 ].…”