Thermoelectric materials are special types of semiconductors that function as "heat pumps" and as heat-to-electricity converters. Thermoelectric power generation allows for small size, high reliability, and quiet operation. Efficient thermoelectric-based heat-to-electricity converters require higher performance materials than are currently available.[1, 2] Direct conversion of heat to electricity could be achieved with solidstate devices based on thermoelectric materials. These devices could play an important role in future energy production, conversion, management, and utilization. When a temperature gradient is created across a thermoelectric

Thermoelectric (TE) power generation has come to be appreciated as an attractive means of low-cost conversion of waste heat to useful electrical energy with a small environmental impact. For a compound to qualify as an efficient thermoelectric material it should exhibit the highest TE figure of merit, ZT, possible at the temperature of operation, T. ZT is defined asand it involves the simultaneous manipulation of the TE power (absolute Seebeck coefficient) S, the electrical conductivity r, and the thermal conductivity j. The search for efficient TE materials mainly focuses on degenerate semiconductors since the underlying physics of these systems allow the coexistence of high thermopower values with high electrical conductivity to achieve high power factors: PF = S 2 r. The Seebeck coefficient is inversely related to the electrical conductivity according to the Boltzmann transport equation, and, as a result, maximization of one cannot be achieved without minimization of the other. An interesting alternative that has been recently suggested to achieve high power factors is the quantum-confinement effect; however, definite experimental verification of this is still lacking.[1]Another route to achieving high-performance TEs is through the minimization of the thermal conductivity. To this end, many suggestions have been made to increase ZT. These include the phonon-glass electron-crystal approach [2] (where loosely bound atoms rattle in cage structures [3] ) as in clathrates, [4] and the thin-film multilayer approach where the introduction of interfaces significantly reduces phonon propagation.[ [10] where compositional fluctuations at the nanoscopic level, resulting in a distinct type of nanostructuring, seem to play a key role in the previously reported very low thermal conductivity. [11] In contrast to the thin-film multilayers, bulk nanocomposite systems offer the advantages of large-scale industrial production and the sustenance of large thermal gradients for extended time. The challenge, therefore, lies in identifying equally efficient p-type materials so that they can be employed in the fabrication of TE modules.Here we report on the Ag(Pb 1 -y Sn y ) m SbTe 2 + m series and show that certain compositions exhibit high performance p-type TE properties (e.g., ZT ∼ 1.45 at 630 K) as a result of their very low thermal conductivity. We show as well that the Ag(Pb 1 -y Sn y ) m SbTe 2 + m systems are in fact bulk nanocomposites. We demonstrate that varying the m and y values, as well as the Ag and Sb concentrations, allows for control over a wide range of properties such as carrier concentration, TE power, and thermal conductivity. These exceptional properties, derived from specific compositions, outperform the standard state-of-the-art p-type systems like TAGS ((AgSbTe 2 ) 0.15 (GeTe) 0.85 , ZT ∼ 1.2 at 720 K [12] ), PbTe (ZT ∼ 0.7 at 740 K [13] ), and Zn 4 Sb 3 (ZT ∼ 1.3 at 670 K [14] ).The electronic-transport properties of the Ag(Pb 1 -y Sn y ) mSbTe 2 + m system can be tuned primarily through carefully control...

Thermoelectric heat-to-electrical-energy converters will play a role in energy management if efficient, stable, and inexpensive materials can be developed. Research to increase the figure of merit ZT is focused on a variety of novel thermoelectric materials and approaches. [1][2][3][4][5][6][7][8][9] Significant advances have come in recent years from the development of nanostructured semiconductors both in thin-film [10] and bulk form. [11][12][13][14] In the thin films, values ZT > 3 have been claimed for PbTe/PbSe superlattice structures, [15] while values of 1.5-1.7 at 700 K have been reported for AgPb 18 SbTe 20, [12] NaPb 20 SbTe 22 , [16] PbTe-PbS, [17] and Tl-PbTe. [18] This progress promises to impact several energy-conversion applications. The advancements have primarily come from sizeable reductions in thermal conductivity, which is largely the result of the scattering of mid-and long-wavelength phonons at the interfaces of the nanoscale inclusions at high temperature. [18,19] Although further increases in ZT can be anticipated by additional reduction of the thermal conductivity, a lower limit is expected to be reached. Thus, dramatic enhancements in ZT can only come from spectacular increases in the power factor (S 2 s). This problem is harder to tackle, since standard charge-transport theory does not offer specific guidance on how to dramatically increase the power factor. Its solution will require breakthroughs in the understanding and control of charge-transport mechanisms in complex materials. An important factor affecting charge transport (e.g. mobility m = et/m, where m is the carrier effective mass) and thus power factor in solids is the relaxation time t, which has an energy dependence [Eq. (1), where E is the energy and r is ascattering parameter]. [20] This relationship implies that the energy dependence of t impacts the mobility, electrical conductivity (s = N em, N = carrier concentration), and thermopower in semiconductors, especially for large values of r owing to their dependence on the relaxation time. In PbTe it is not possible to cause significant changes in the scattering mechanism by making solid solutions or through carrier doping.[21] A more fundamental question is whether the relative contributions of known scattering mechanisms, or even the actual mechanisms themselves in PbTe, can be altered through nanostructuring. For example, can features buried on the nanoscale fundamentally change the electronic structure and therefore charge transport?We report herein a new way to achieve dramatic changes in the carrier transport in PbTe, which leads to large increases in the thermoelectric power factor (S 2 s) at high temperatures. We observe the enhancements only when PbTe is co-nanostructured with two different phases. We show that when lead and antimony are present simultaneously as nanodots throughout the matrix of PbTe, the conductivity behavior becomes novel. We observe unprecedented temperature dependence that is a complicated function of the Pb/Sb ratio. The most important conse...

The series of Pb(9.6)Sb(0.2)Te(10)(-)(x)Se(x) compounds with different Se content (x) were prepared, and their structure was investigated at the atomic and nanosized regime level. Thermoelectric properties were measured in the temperature range from 300 to 700 K. The Pb(9.6)Sb(0.2)Te(10)(-)(x)Se(x) series was designed after the refinement of the single-crystal structure of Pb(3.82)Sb(0.12)Te(4) (Pb(9.6)Sb(0.3)Te(10); S.G. Pmm) by substituting isoelectronically in anion positions Te by Se. The Pb(9.6)Sb(0.2)Te(10)(-)(x)Se(x)() compounds show significantly lower lattice thermal conductivity (kappa(L)) compared to the well-known PbTe(1)(-)(x)Se(x) solid solutions. For Pb(9.6)Sb(0.2)Te(3)Se(7) (x = 7), a kappa(L) value as low as 0.40 W/m.K was determined at 700 K. High-resolution transmission electron microscopy of several Pb(9.6)Sb(0.2)Te(10)(-)(x)Se(x) samples showed widely distributed Sb-rich nanocrystals in the samples which is the key feature for the strong reduction of the lattice thermal conductivity. The reduction of kappa(L) results in a significantly enhanced thermoelectric figure of merit of Pb(9.6)Sb(0.2)Te(10)(-)(x)Se(x) compared to the corresponding PbTe(1)(-)(x)Se(x) solid solution alloys. For Pb(9.6)Sb(0.2)Te(3)Se(7) (x = 7), a maximum figure of merit of ZT approximately 1.2 was obtained at approximately 650 K. This value is about 50% higher than that of the state-of-the-art n-type PbTe. The work provides experimental validation of the theoretical concept that embedded nanocrystals can promote strong scattering of acoustic phonons.

Thermoelectric materials are special types of semiconductors that function as "heat pumps" and as heat-to-electricity converters. Thermoelectric power generation allows for small size, high reliability, and quiet operation. Efficient thermoelectric-based heat-to-electricity converters require higher performance materials than are currently available.[1, 2] Direct conversion of heat to electricity could be achieved with solidstate devices based on thermoelectric materials. These devices could play an important role in future energy production, conversion, management, and utilization. When a temperature gradient is created across a thermoelectric