Achieving High Carrier Mobility And Thermal Stability in Plainified Rhombohedral GeTe Thermoelectric Materials with zT > 2

Abstract

GeTe is a very promising thermoelectric material, but the presence of massive intrinsic Ge vacancies leads to an overhigh hole concentration and poor thermal stability. Counter doping is commonly employed to reduce the hole concentration, which, however, unavoidably deteriorates the carrier mobility. Here, it is found that the intrinsic hole concentration in the rhombohedral phase is much lower than that in the cubic phase, owing to the higher formation energy of Ge vacancy in the former. With this recognition, the hole concentration of GeTe can be tuned to its optimum value simply by annealing below the phase transition temperature. As a result, “compositional plainification” is realized in the high‐performance GeTe‐based thermoelectrics with significantly reduced amounts of counter dopants and hetero‐alloys. A high carrier mobility of 150 cm2 V−1 s−1 is realized in GeTe at 300 K, which is much higher than that in conventional counter‐doped ones (≤60 cm2 V−1 s−1). More importantly, GeTe‐based compounds, with suppressed intrinsic vacancies, exhibit good thermal stability and reproducibility of thermoelectric performance. A high peak figure of merit, zT, of 2.14 at 670 K is obtained in Ge0.93Bi0.03Pb0.04Te. This work highlights the importance of understanding and regulating the intrinsic vacancy for high‐performance GeTe thermoelectrics.

Ostwald Ripening of Ag2Te Precipitates in Thermoelectric PbTe: Effects of Crystallography, Dislocations, and Interatomic Bonding

“…Figure 5c shows a considerable enhancement of µ w upon thermal annealing treatment. This can be attributed to four factors based upon the structural characterizations: i) the lowered number density of Ag 2 Te precipitates; ii) the decreased concentration of Ag in the matrix; iii) the increased concentration of Pb and thus reduced content of Pb vacancy in the matrix, i.e., lattice plainification [ 66,67 ] ; and iv) the relaxed strain generated by supersaturated GP zones and platelet precipitates in the as‐quenched sample upon annealing. As a consequence, the PF is enhanced upon annealing as shown in Figure 5d.…”

A comprehensive review of entropy engineered GeTe: an antidote to phase transformation

“…In this scenario, the carrier mobility is not compromised and high ZT is obtained. 156,157 The systematic investigation of IV-VI chalcogenides with the thermodynamic landscape of (Ge,Sn,Pb)(S,Se,Te) (as shown in Fig. 24) reveals that a Gepoor composition at the cationic site and S-poor composition at the anionic site are stable with low phase transition temperature and easy to synthesize.…”

Lattice Plainification Leads to High Thermoelectric Performance of P‐Type PbSe Crystals

“…The 𝜎 is affected by the carrier concentration (n) and carrier mobility (μ). Based on perspectives in recent works, increasing the μ is an effective strategy to enhance the thermoelectric performance of materials at near room temperatures, [6,[36][37][38] such as texturing, [39,40] modulation doping, [41,42] band engineering, [43,44] symmetry enhancement, [45,46] crystal preparation, [47][48][49][50] lattice plainification, [1,51,52] and so on. [53] In this work, the μ of p-type PbSe material was significantly enhanced by physical vapor deposition (PVD) and lattice plainification.…”

“…The lattice plainification strategy refers to the atomic-level lattice modification, which was successfully applied in SnSe [1] and GeTe systems. [52] Introducing atoms to fill vacancy defects within the lattice, aims to mitigate the carrier scattering induced by defects, facilitating faster carrier transport, enhancing carrier mobility, and consequently improving thermoelectric performance near room temperature. [36] As illustrated in Figure 1A, the schematic diagram elucidates the process of this work.…”