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Modification of crystal symmetry induced by chemical doping or alloying is well known to optimize the charge carrier transport properties in thermoelectric materials. Historically, the altered defect chemistry of the targeted materials, however, has long been neglected or underestimated, which may, in turn, favorably or adversely affect the thermoelectric properties. Herein, using a case study of thermoelectric GeTe, first, the hidden role of rhombohedral distortion degree on the Ge‐vacancy formation energy is theoretically unraveled, and it is experimentally found that Sc and Bi codoping realize a superior thermoelectric performance. Density functional theory calculations demonstrate that the distorted rhombohedral lattice closer to cubic would unexpectedly induce the significantly decreased formation energy of Ge vacancies, resulting in the spontaneous formation of higher‐concentration Ge vacancies. Sc doping is found to be the most effective dopant to reduce the carrier concentration without obviously affecting the rhombohedral distortion degree, leading to the realization of a record‐high power factor. Benefiting from the suppressed thermal conductivity by further Bi doping, an ultrahigh average ZT ≈1.2 from 300 to 723 K is achieved. These discoveries provide new insights into the relationship between crystal symmetry and defect chemistry, and also promote GeTe materials for future thermoelectric applications. [ABSTRACT FROM AUTHOR]

In this study, thermoelectric properties of MgTi 2 O 5 -based composites were investigated. 10–30 vol.% TiN were added as a conductive reinforcement phase. MgTi 2 O 5 /TiN composites were successfully synthesized at 1373 K for 10 min via reactive spark plasma sintering. The present SPS process itself enhanced electrical conductivity of MgTi 2 O 5 more than 250 times while effectively suppressing thermal conduction by defect engineering. Moreover, compositing further remarkably improved its electrical conductivity, and hence large enhancements in the thermoelectric power factor and ZT value were achieved. The results indicate a new doping technique in MgTi 2 O 5 and enhancing thermoelectric properties of other insulating oxide materials. Image, graphical abstract [ABSTRACT FROM AUTHOR]

p -type TlSbTe 2 and its In- and Yb-doped variants were prepared by hot pressing of the elements in the stoichiometric ratios, and their thermoelectric properties were determined after verifying the purity of the samples by powder X-ray diffraction. Theoretically, TlSbTe 2 is an intrinsic semiconductor possessing a narrow band gap; however, the as-prepared TlSbTe 2 exhibited relatively high electrical conductivity, decreasing with ascending temperature, which provides evidence for the presence of p -type extrinsic charge carriers (holes) along with the positive Seebeck coefficient. Doping In onto the Tl site inserts more electrons, thereby decreasing the hole concentration; as a result, the electrical and thermal conductivity decreased and the Seebeck coefficient increased. The best thermoelectric performance of In-doped TlSbTe 2 was achieved at 625 K, with a figure of merit (zT) of 0.77. The overall best zT was improved to 0.85 at 620 K with the sample of nominal composition Tl 0.98 SbYb 0.02 Te 2. An anisotropy test was implemented by comparing the electrical conductivity and Seebeck coefficient measured on the prismatic bars cut parallel and vertical to the pressing direction. The results indicate basically isotropic behavior in polycrystalline TlSbTe 2 along these two orthogonal directions. • TlSbTe2 is bestowed with an extraordinarily low thermal conductivity. • Our processing conditions caused an increase in the figure-of-merit by 15%. • Doping with Yb caused a further increase by an additional 20%, for a total increase of 39%. • Doping with In led to no significant changes in performance. • Direction-dependent measurements revealed no significant anisotropies in the electrical properties. [ABSTRACT FROM AUTHOR]

In the first part of this work, thallium lanthanide tellurides with composition Tl 9 LnTe 6 (Ln = La, Ce, Pr, Nd, Sm, Gd, Tb) have been prepared and their high temperature electrical and thermal transport properties investigated. Nearly single phase samples were obtained. Rietveld refinement results showed that Tl 9 CeTe 6 had an exceptionally small unit cell volume of 1033 Å 3 . The electrical conductivity and thermal conductivity increased across the lanthanide series from La to Tb. On the other hand, the Seebeck coefficient values decreased with Ln varying from La to Tb. Tl 9 SmTe 6 or Tl 9 GdTe 6 constituted an exception, as the Seebeck coefficient of Tl 9 SmTe 6 was smaller than that of Tl 9 GdTe 6 . Tl 9 LaTe 6 has the largest figure-of-merit of this series. Thereafter, Tl 10 − x La x Te 6 samples were prepared with x = 0.90, 0.95, 1.00, 1.05, 1.10, aiming toward higher zT through composition optimization and expanding of the measurement temperature range. With the increasing La content, the unit cell volume increased, while the electrical conductivity, thermal conductivity and lattice thermal conductivity decreased, and the Seebeck coefficient increased. The highest zT = 0.57 was observed for Tl 9 LaTe 6 at 600 K. [ABSTRACT FROM AUTHOR]

Noting the steadily worsening problem of depleted fossil fuel sources, alternate energy sources have become increasingly important; these include thermoelectrics, which may use waste heat to generate electricity. To be economically viable, the thermoelectric figure-of-merit, zT, which is related to the energy conversion efficiency, needs to be in excess of unity ( zT > 1). Tl4SnTe3 and Tl4PbTe3 were reported to attain a thermoelectric figure-of-merit zTmax = 0.74 and 0.71, respectively, at 673 K. Here, the thermoelectric properties of both materials are presented as a function of x in Tl10- xSn xTe6 and Tl10- xPb xTe6, with x varying between 1.9 and 2.05, culminating in zT values in excess of 1.2. These materials are charge balanced when x = 2, according to (Tl+)8(Sn2+)2(Te2−)6 and (Tl+)8(Pb2+)2(Te2−)6 (or: (Tl+)4Pb2+(Te2−)3). Increasing x causes an increase in valence electrons, and thus a decrease in the dominating p-type charge carriers. Larger x values occur with a smaller electrical conductivity and a larger Seebeck coefficient. In each case, the lattice thermal conductivity remains under 0.5 W m−1 K−1, resulting in several samples attaining the desired zTmax > 1. The highest values thus far are exhibited by Tl8.05Sn1.95Te6 with zT = 1.26 and Tl8.10Pb1.90Te6 with zT = 1.46 around 685 K. [ABSTRACT FROM AUTHOR]

Noting the steadily worsening problem of depleted fossil fuel sources, alternate energy sources have become increasingly important; these include thermoelectrics, which may use waste heat to generate electricity. To be economically viable, the thermoelectric figure-of-merit, zT, which is related to the energy conversion efficiency, needs to be in excess of unity ( zT > 1). Tl4SnTe3 and Tl4PbTe3 were reported to attain a thermoelectric figure-of-merit zTmax = 0.74 and 0.71, respectively, at 673 K. Here, the thermoelectric properties of both materials are presented as a function of x in Tl10- xSn xTe6 and Tl10- xPb xTe6, with x varying between 1.9 and 2.05, culminating in zT values in excess of 1.2. These materials are charge balanced when x = 2, according to (Tl+)8(Sn2+)2(Te2−)6 and (Tl+)8(Pb2+)2(Te2−)6 (or: (Tl+)4Pb2+(Te2−)3). Increasing x causes an increase in valence electrons, and thus a decrease in the dominating p-type charge carriers. Larger x values occur with a smaller electrical conductivity and a larger Seebeck coefficient. In each case, the lattice thermal conductivity remains under 0.5 W m−1 K−1, resulting in several samples attaining the desired zTmax > 1. The highest values thus far are exhibited by Tl8.05Sn1.95Te6 with zT = 1.26 and Tl8.10Pb1.90Te6 with zT = 1.46 around 685 K. [ABSTRACT FROM AUTHOR]

Thermoelectric thin films are of great interest for self-powering Internet of Things (IoT) nodes via energy harvesting. Heusler-type Fe 2 VAl attracts some attention for room-temperature thermoelectric applications. However, the large overall thermal conductivity leads to a poor performance that restricts the current investigations. Herein, we report a comprehensive study of structural, thermoelectric, and magnetic properties of Fe 2 V 0.9 Ti 0.1 Al thin films on quartz substrate, grown by magnetron sputtering. It is found that high-temperature annealing is more effective than the long-time annealing at the low temperatures to stabilize the L 2 1 type structure of Fe 2 VAl, leading to a much larger Seebeck coefficient and slightly higher thermal conductivity. More importantly, the significant off-stoichiometry phenomenon, namely Fe-rich composition, contributes to n-type conduction of thin films. Both the picosecond and nanosecond time-domain thermoreflectance techniques were employed to successfully measure the thin-film thermal conductivities, merely one-third of bulk material, demonstrating the effectiveness of utilizing nanostructuring to reduce the thermal conductivity of Fe 2 VAl. Moreover, magnetic susceptibility measurements reveal that thin films are ferromagnets, while the bulk sample is characterized by paramagnetism. Our finding sheds new light on the composition-structure-property relationship of Fe 2 VAl thin films for future related applications. Image, graphical abstract The significant off-stoichiometry of Ti doped Fe 2 VAl films in the L2 1 type structure grown on quartz substrate leads to the unexpected n-type conduction and strong ferromagetism, which are may be helpful for thermoelectric, magnetoelectronic, and also spintronic applications. [ABSTRACT FROM AUTHOR]

The synthesis of pure pristine and vanadium-doped MnSi γ (γ = 1.74) powder by a relatively fast, 'low temperature' and high yield magnesioreduction process is described. The powder obtained by this innovative route is composed of well crystallized grains with sizes ranging from 20 to 500 nm and free from any MnSi precipitates. Mesostructured densified pellets with average grain sizes as small as 550 nm are obtained by spark plasma sintering (SPS). Detailed structural and microstructural characterization of the samples were realized at every stage of the process, highlighting a high concentration of defects such as orientational or spacing anomalies of the Nowotny phase, γ variations within a single grain and dislocations. Accordingly a significant decrease of the lattice thermal conductivity is evidenced in comparison to conventionally synthesized (arc-melting/SPS) samples having similar density and (V/)Mn/Si stoichiometry. The thermoelectric properties of these materials are discussed in regard of their complex microstructure. Image 1 • Mesostructured higher manganese silicides are synthesized by magnesioreduction. • Crystal structures are refined in composite-incommensurate unit-cells. • Microstructures are examined by EBSD and TEM. • The decrease in thermal conductivity is correlated to the microstructure. [ABSTRACT FROM AUTHOR]