High-performance nanostructured thermoelectric materials

Abstract

T he conversion of thermal energy to electrical energy is known as thermoelectric (TE) conversion. Th e TE eff ect can be used for both power generation and electronic refrigeration. When a temperature gradient (ΔT ) is applied to a TE couple consisting of n-type (electron-transporting) and p-type (hole-transporting) elements, the mobile charge carriers at the hot end tend to diff use to the cold end, producing an electrostatic potential (ΔV ). Th is characteristic, known as the Seebeck eff ect, where α = ΔV/ΔT is defi ned as the Seebeck coeffi cient, is the basis of TE power generation, as shown in Figure 1(a). Conversely, when a voltage is applied to a TE couple, the carriers attempt to return to the electron equilibrium that existed before the current was applied by absorbing energy at one connector and releasing it at the other, an eff ect known as the Peltier eff ect, as shown in Figure 1(b). Th ermoelectric technology and solid-state devices based on the TE eff ect have a number of advantages, including having no moving parts, and being reliable and scalable. Th e technology has therefore arouse worldwide interest in many fi elds, including waste heat recovery and solar heat utilization (power generation mode), and temperature-controlled seats, portable picnic coolers and thermal management in microprocessors (active refrigeration mode) [1].Th e effi ciency of TE devices is strongly associated with the dimensionless fi gure of merit (ZT) of TE materials, defi ned as ZT = (α 2 σ/κ)T, where σ, κ and T are the electrical resistivity, thermal conductivity and absolute temperature [2]. High electrical conductivity (corresponding to low Joule heating), a large Seebeck coeffi cient (corresponding to large potential diff erence) and low thermal conductivity (corresponding to a large temperature diff erence) are therefore necessary in order to realize high-performance TE materials. Th e ZT fi gure is also a very convenient indictor for evaluating the potential effi ciency of TE devices. In general, good TE materials have a ZT value of close to unity. However, ZT values of up to three are considered to be essential for TE energy converters that can compete on effi ciency with mechanical power generation and active refrigeration.High-performance TE materials have been pursued since Bi 2 Te 3 -based alloys were discovered in the 1960s. Until the end of last century, moderate progress had been made in the development of TE materials. Th e benchmark of ZT ≈ 1 was broken in the mid-1990s by two Tsinghua University, China Thermoelectric eff ects enable direct conversion between thermal and electrical energy and provide an alternative route for power generation and refrigeration. Over the past ten years, the exploration of high-performance thermoelectric materials has attracted great attention from both an academic research perspective and with a view to industrial applications. This review summarizes the progress that has been made in recent years in developing thermoelectric materials with a high dimensionless fi gure of...

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“…[78] The difference may be caused by the presence of excess amount grain boundaries, which can decrease the thermal conductivity at the cost of electrical conductivity. [79][80][81] The thermoelectric properties of the Bi2Se3 pellet are presented in Figure 8 , the ZT value of our Bi2Se3 pellet is apparently higher than the literature value [82] and reaches 0.27 at 230 °C. The higher ZT is mainly due to the ultralow thermal conductivity caused by the presence of nanograins.…”

“…The higher ZT is mainly due to the ultralow thermal conductivity caused by the presence of nanograins. [79][80][81] dependence of ZT for our sample with that of single-crystal SnSe. [83] The maximum ZT of our sample is 0.38 at 300 °C, higher than that of single crystal SnSe (ZT = 0.21) at the same temperature.…”

Thermoelectric performance enhancement in n-type Bi2(TeSe)3 alloys owing to nanoscale inhomogeneity combined with a spark plasma-textured microstructure

“…[1][2][3][4] The thermoelectric conversion efficiency of a material depends on its dimensionless figure of merit ZT, defined as ZT = α 2 σT/κ, where α, σ, κ and T are the Seebeck coefficient, electrical conductivity, thermal conductivity and absolute temperature, respectively. 5,6 A great variety of thermoelectric materials have been developed and thoroughly studied, [7][8][9] but industrial applications are still dominated by bismuth telluride (Bi 2 Te 3 )-based alloys.…”

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