Fabrication of thermoelectric materials – thermal stability and repeatability of achieved efficiencies

Abstract

Metal chalcogenides have delivered the highest efficiencies among thermoelectric materials. Although the thermal stability of thermoelectric materials at device operating temperatures has been of concern, recent studies have reported the efficiencies of materials prepared with different fabrication techniques. Here, we have fabricated a p-type, multiphase lead chalcogenide compound of (PbTe)0.55(PbS)0.35(PbSe)0.1, with three common fabrication techniques of quenched, quenched-annealed and furnace cooled followed by spark plasma sintering. The compound contains PbS-rich precipitates within a PbTe-rich matrix. The achieved samples from various fabrication procedures demonstrate distinct microstructures that evolve with thermal cycling. We have shown that the thermoelectric efficiency of metastable compound is irreversible during thermal cycling, and changes by only three thermal cycles during measurements. Our findings highlight the importance of the choice of fabrication and post-processing techniques for thermoelectric materials.

Thermoelectric Performance of Single Phase p-Type Quaternary (PbTe)0.65–x(PbSe)0.35(PbS)x Alloys

“…The ternary PbTe–PbSe and PbSe–PbS systems have unlimited solubility over the entire composition range and, as such, are always solid solutions. , Nevertheless, the components of the PbTe–PbS system show very limited solubility with respect to each other, and phase separation of PbS precipitates in the PbTe matrix on the PbTe-rich side of the phase diagram occurs via nucleation and growth. This behavior is also observed in the quaternary system PbTe–PbSe–PbS, where the addition of PbS causes a secondary phase to appear . A large amount of PbSe increases the solubility of PbS in PbTe, allowing (PbTe) 0.65– x (PbSe) 0.35 (PbS) x samples to still behave as solid solutions with a large concentration of PbS in the PbTe matrix.…”

“…Sodium is a commonly used p-type dopant for lead chalcogenides, , and in heavily doped multiphase PbTe-PbS samples, a large percentage of sodium will partition to the secondary PbS phase. This sodium segregation is detrimental to performance; therefore, single phase sodium-doped PbTe is of interest in order to maximize the power factor.…”

Enhanced ZT of InxCo4Sb12–InSb Nanocomposites Fabricated by Hydrothermal Synthesis Combined with Solid–Vapor Reaction: A Signature of Phonon-Glass and Electron-Crystal Materials

“…However, materials with high thermal conductivity and large power factor σ S 2 are favorable for achieving high efficiency in the case of thermoelectric coolers . Fabricating materials with ZT higher than available values to achieve application goals in generating the electrical energy has received major ongoing research challenges. − In this regard, various strategies such as tuning the electronic structure via introducing extrinsic carrier through doping and/or alloying are adopted to enhance the power factor σ S 2 . ,,,,, Furthermore, electron energy filtering and band offset minimization strategies have been developed for enhancing the power factor of the nanostructured thermoelectrics. ,,,, In addition, decreasing the lattice component of the total thermal conductivity via broad-based phonons scattering from hierarchical nanostructures is progressively investigated. − Recently, fabrication of microcomposites embedded with nanoinclusions is found to be a practical strategy for enhancing ZT. ,,− Nanocomposites have been proven to be capable of enhancing the power factor by tuning the electronic properties and simultaneously suppressing the lattice thermal conductivity by progressing all-scale hierarchical phonon scattering. , Hence, fabricating nanocomposites could be one of the straightforward strategies toward producing phonon-glass electron-crystal (PGEC) thermoelectric materials. , Intrinsically possessing two Sb-icosahedral voids per unit cell, the Co 8 Sb 24 skutterudite is among the potential thermoelectric materials capable for exhibiting PGEC properties. , However, the relatively high lattice thermal conductivity (>9 Wm –1 K –1 around room temperature) degrades the thermoelectric performance of the pristine bulk cobalt skutterudite . Formation of ternary analogues or solid solutions and filling the intrinsic voids could be effective strategies for reducing the thermal conductivity of skutterudite. − Selectively filling the Sb -voids by various elements enhances the power factor via modifying the charge carriers concentration and to some extent decreases the lattice thermal conductivity via rattling-assisted phonon scattering.…”

Recent Progress in Multiphase Thermoelectric Materials

“…Copper telluride in Bi 0.5 Sb 1.5 Te 3 [228] and a composite of ZnSb matrix with minority phases of Zn 4 Sb 3 , Zn 3 P 2 , and Cu 5 Zn 8 [229] have shown higher electrical conductivity. It should be noted that the values of electronic transport properties are greatly dependent on the fabrication methods [230], quality of the raw materials, and oxidisation of the material [231][232][233].…”