No abstract

The potential of thermoelectric materials to generate electricity from the waste heat can play a key role in achieving a global sustainable energy future. In order to proceed in this direction, it is essential to have thermoelectric materials that are environmentally friendly and exhibit high figure of merit, ZT. Oxide thermoelectric materials are considered ideal for such applications. High thermoelectric performance has been reported in single crystals of Ca3Co4O9. However, for large scale applications single crystals are not suitable and it is essential to develop high-performance polycrystalline thermoelectric materials. In polycrystalline form, Ca3Co4O9 is known to exhibit much weaker thermoelectric response than in single crystal form. Here, we report the observation of enhanced thermoelectric response in polycrystalline Ca3Co4O9 on doping Tb ions in the material. Polycrystalline Ca3−xTbxCo4O9 (x = 0.0–0.7) samples were prepared by a solid-state reaction technique. Samples were thoroughly characterized using several state of the art techniques including XRD, TEM, SEM and XPS. Temperature dependent Seebeck coefficient, electrical resistivity and thermal conductivity measurements were performed. A record ZT of 0.74 at 800 K was observed for Tb doped Ca3Co4O9 which is the highest value observed till date in any polycrystalline sample of this system.

No abstract

No abstract

No abstract

Tin selenide (SnSe) is a promising thermoelectric material because of its advantageous electronic structures and low thermal conductivity. In this work, n-type polycrystalline SnSe0.95 doped by a new dopant NbCl5...

NaxCoO2 was known 20 years ago as a unique example in which spin entropy dominates the thermoelectric behavior. Hitherto, however, little has been learned about how to manipulate the spin degree of freedom in thermoelectrics. Here, we report the enhanced thermoelectric performance of GeMnTe2 by controlling the spin’s thermodynamic entropy. The anomalously large thermopower of GeMnTe2 is demonstrated to originate from the disordering of spin orientation under finite temperature. Based on the careful analysis of Heisenberg model, it is indicated that the spin-system entropy can be tuned by modifying the hybridization between Te-p and Mn-d orbitals. As a consequent strategy, Se doping enlarges the thermopower effectively, while neither carrier concentration nor band gap is affected. The measurement of magnetic susceptibility provides a solid evidence for the inherent relationship between the spin’s thermodynamic entropy and thermopower. By further introducing Bi doing, the maximum ZT in Ge0.94Bi0.06MnTe1.94Se0.06 reaches 1.4 at 840 K, which is 45% higher than the previous report of Bi-doped GeMnTe2. This work reveals the high thermoelectric performance of GeMnTe2 and also provides an insightful understanding of the spin degree of freedom in thermoelectrics.

GeTe-based compounds are promising thermoelectric materials at medium temperature, while the performance of the GeTe matrix is at the mercy of its high hole concentration and high thermal conductivity. This work reports the thermoelectric performance optimization of GeTe by alloying with CuSbSe2. With only 5% CuSbSe2 being introduced, the p-type hole concentration is greatly decreased from ∼1021 to ∼1020 cm–3, and the thermal conductivity at room temperature is reduced by more than 70%. Interestingly, the alloying of CuSbSe2 also induces a crystal structure transition of GeTe which results in the cubic structure of GeTe at room temperature, in spite of the noncubic structure of orthorhombic CuSbSe2. Owing to the phase transition and carrier concentration optimization, the thermoelectric performance is largely improved relative to the pristine compound. Eventually, a ZTmax ∼ 1.65 is achieved at 630 K. It is also indicated that the performance of GeTe–CuSbSe2 could be further improved by the careful tuning of carrier concentration.