Thermoelectric materials have potential applications in energy harvesting and electronic cooling devices, and bismuth antimony telluride (BiSbTe) alloys are the state-of-the-art thermoelectric materials that have been widely used for several decades. It is demonstrated that mixing SiC nanoparticles into the BiSbTe matrix effectively enhances its thermoelectric properties; a high dimensionless fi gure of merit ( ZT ) value of up to 1.33 at 373 K is obtained in Bi 0.3 Sb 1.7 Te 3 incorporated with only 0.4 vol% SiC nanoparticles. SiC nanoinclusions possessing coherent interfaces with the Bi 0.3 Sb 1.7 Te 3 matrix can increase the Seebeck coeffi cient while increasing the electrical conductivity, in addition to its effect of reducing lattice thermal conductivity by enhancing phonon scattering. Nano-SiC dispersion further endows the BiSbTe alloys with better mechanical properties, which are favorable for practical applications and device fabrication.

. IntroductionThermoelectric (TE) materials have drawn increasing attention because of their potential applications in energy harvesting and electronic cooling devices. [ 1,2 ] The performance of a thermoelectric material is defi ned by its dimensionless fi gure of merit ZT = α 2 ( ρ κ ) −1 T , where α is the Seebeck coeffi cient (also called as thermopower), T is the absolute temperature, ρ is the electrical resistivity, and κ is the thermal conductivity. [ 3 ] Extensive research has been carried out attempting to discover thermoelectric materials with higher performance. [4][5][6][7][8][9][10] Among different types of TE materials, lead telluride (PbTe) has demonstrated a relatively high ZT value in the medium temperature region, which makes it a suitable material for power generation rather than cooling applications. [ 11 ] Many studies have been focused on the doping of PbTe alloys to optimize its carrier concentration, [ 12,13 ] manipulate its electronic density of states, [ 14 ] microstructure [ 15 ] as well as endotaxial nanostructure. [16][17][18] In 2004, Hsu et al. fi rst reported high ZT values of PbTe-based AgPb m SbTe m +2 alloys, which were abbreviated as LAST alloys by taking the names of constitutive elements. [ 19 ] The main contribution to the high ZT value in LAST alloys is their nanostructure feature with nanoscopic precipitates or nanodots with compositional fl uctuation, which reduces thermal conductivity due to enhanced phonon scattering but not greatly affects electrical conduction, owing to the endotaxial interface between the precipitates and the matrix. [ 19 ] In fact, our previous study revealed that thermal conductivity and electrical resistivity can be reduced at the same time by a traditional annealing treatment that facilitated the in-situ formation of precipitates of 5-20 nm in diameter. [ 20 ] A recent study has shown that optimization of hierarchical architecture from mesoscale grains and grain boundaries to nanoscale endotaxial precipitates is effective for further ZT enhancement. [ 21 ] This work recalled the importance of controlling grain-level microstructure, which can be easily realized in most thermoelectric materials. It is well known that refi ning microstructure by reducing grain sizes is a general approach to lowering the thermal conductivity. In fact, great ZT enhancement has been achieved in several kinds of thermoelectric alloys, and among them a good example is that signifi cant ZT elevation can be realized in half-Heusler alloys that have high thermal conductivity, which can be signifi cantly lowered by reducing grain sizes [ 22 ] or via a nanocomposite approach. [ 23 ] It was reported that grain refi nement could also lead to an increase in Seebeck coeffi cient in some thermoelectric materials due to an enhanced energy fi ltering effect at grain boundaries. [ 15,24 ] With a motivation to further increase the thermoelectric performance, a repeated mechanical alloying (MA)-spark plasma sintering (SPS) method was applied to the fabrication of LAST alloys and was in...

For further thermoelectric performance enhancement by the nanocomposite effect, a small amount (<2 vol. %) of 30 nm SiC particles were added into a compositionally optimized AgPb m SbTe mþ2 thermoelectric alloy fabricated by mechanical alloying and spark plasma sintering. Although the energy filtering effect is not available in the present composite due to the mismatched interface between SiC and the matrix, a small amount of SiC dispersions were revealed to be effective to reduce the thermal conductivity via enhancing phonon scattering. A high figure of merit up to 1.54 at 723 K was obtained in the AgPb m SbTe mþ2 matrix composite containing 1 vol. % SiC nanoparticles. V C 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4869220] Thermoelectric materials have drawn increasing attention because of their potential in energy harvesting and electronic cooling device applications. 1-3 The efficiency of thermoelectric conversion depends on the dimensionless figure of merit, ZT, defined as ZT ¼ a 2 (qj) À1 T, where a is the Seebeck coefficient (also called as thermopower), T is the absolute temperature, q is the electrical resistivity, and j is the thermal conductivity, 4 respectively. It is not easy to independently control these parameters to improve the ZT value because of the coupling relationship among a, q, and j. In last ten years, nanostructuring in the form of quantum well, 5 superlattice, 6 nanodot, 7,8 as well as nanostructured bulk composites 9,10 have shed new light on the improvement of thermoelectric materials, where they can significantly reduce thermal conductivity without affecting electrical properties, even improvement in some cases. Enhanced thermoelectric performance in many materials with ZT > 1 or ZT % 1 has been reported, such as Bi 2 Te 3 , 11,12 PbTe/PbS, 13-15 and oxide compounds. 16 Especially, in PbTe-based AgPb m SbTe mþ2 (LAST, lead-antimony-silver-tellurium) compounds, a high ZT value up to 1.7 at 700 K was achieved by Hsu et al. in 2004. 17 Previous studies 9,17,18 indicated that the endotaxial nanostructure is very effective in enhancing ZT value of LAST alloys, such as the phase-segregation with the presence of embedded nanodots (appear to be rich in Ag and Sb) in the PbTe matrix, which are believed to play an important role in scattering phonons without influencing electron transport meanwhile. However, one may worry about the stability of such a nanostructure when used for a long time at high temperatures. Alternatively, intentionally mixing inert nanoparticles into a thermoelectric matrix should be an easier approach to create composites, which should have more difficulty to grow or coalesce than the in situ precipitates formed by annealing. In fact, it is demonstrated that mixing SiC nanoparticles into the BiSbTe matrix can effectively enhance its thermoelectric and mechanical properties. 19,20 In this work, we explored the effect of incorporating nano-SiC particles in the LAST matrix on the TE properties. The atoms of Si and C are much lighter than those of Pb and Te as t...

Defects in acceptor-doped perovskite piezoelectric materials have a significant impact on their electrical properties. Herein, the defect mediated evolution of piezoelectric and ferroelectric properties of Fe-doped (Pb,Sr)(Zr,Ti)O3 (PSZT-Fe) piezoceramics with different treatments, including quenching, aging, de-aging, and poling, was investigated systematically. Oxygen vacancies with a cubic symmetry are preserved in the quenched PSZT-Fe ceramics, rendering them robust ferroelectric behaviors. In the aged PSZT-Fe polycrystals, defect dipole between Fe dopant and oxygen vacancy has the same orientation with spontaneous polarization PS, which enables the reversible domain switching and hence leads to the emergence of pinched polarization hysteresis and recoverable strain effect. And the defect dipoles can be gradually disrupted by bipolar electric field cycling, once again endowing the aged materials with representative ferroelectric properties. For the poled PSZT-Fe polycrystals, the defect dipoles are reoriented to be parallel to the applied poling field, and an internal bias field aligning along the same direction emerges simultaneously, being responsible for asymmetric hysteresis loops.

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