Inorganic Clathrates for Thermoelectric Applications

Stefanoski, Stevce; Beekman, Matt; Nolas, George S.

doi:10.1007/978-94-017-9127-4_6

Cited by 23 publications

(14 citation statements)

References 125 publications

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“…Such a peak is typical for temperature dependence of thermal conductivity of crystalline insulating/ semiconducting solids. 69,70 Such "glass-like" temperature dependence of thermal conductivity, typical for amorphous materials, suggests that the disordered complex crystal structure in HT-Na 1−x Zn 4−y Sb 3 and "rattling" of Na atoms in the interlayer space in the crystal structure of NaZn 4 Sb 3 (Na atom has large ADPs, Table 2) can be responsible for the phonon scattering at low temperatures.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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From NaZn₄Sb₃ to HT-Na_1–xZn_4–ySb₃: Panoramic Hydride Synthesis, Structural Diversity, and Thermoelectric Properties

et al. 2019

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Two new sodium zinc antimonides NaZn4Sb3 and HT-Na1-xZn4-ySb3 were synthesized by using reactive sodium hydride, NaH, as a precursor. The hydride route provides uniform mixing and comprehensive control over the composition, facilitating fast reactions and high-purity samples, whereas traditional synthesis using sodium metal results in inhomogeneous samples with a significant fraction of the more stable NaZnSb compound. NaZn4Sb3 crystalizes in the hexagonal P63/mmc space group (No. 194, Z = 2, a = 4.43579(4) Å, c = 23.41553(9) Å), and is stable upon heating in vacuum up to 736 K. The layered crystal structure of NaZn4Sb3 is related to the structure of the well-studied thermoelectric antimonides AeZn2Sb2 (Ae = Ca, Sr, Eu). Upon heating in vacuum NaZn4Sb3 transforms to HT-Na1-xZn4-ySb3 (x = 0.047(3), y = 0.135(1)) due to partial Na/Zn evaporation/elimination, as was determined from hightemperature in-situ synchrotron powder X-ray diffraction. HT-Na1-xZn4-ySb3 has a complex monoclinic structure with considerable degrees of structural disorder (P21/c (No. 14, Z = 32), a = 19.5366(7) Å, b = 14.7410(5) Å, c = 20.7808(7) Å, β = 90.317(2)°) and is stable exclusively in a narrow temperature range of 736 − 885 K. Further heating of HT-Na1-xZn4-ySb3 leads to a reversible transformation to NaZnSb above 883 K. Both compounds exhibit similarly low thermal conductivity at room temperature (0.9 W•m −1 K −1 ) and positive Seebeck coefficients (38-52 µV/K) indicative of holes as the main charge carriers. However, resistivities of the two phases differ by two orders of magnitude.Here, we have explored the ternary Na-Zn-Sb system and discovered two new compositionally similar, but structurally different ternary antimonides, both are featuring new structure types. Using the fast hydride route coupled with in-situ high-temperature powder X-ray diffraction experiments, compositional and temperature screening allowed for synthesis of two new ternary phases: NaZn4Sb3 phase and what at first appeared to be its polymorph, but in fact it is a different compound with slightly Na/Zn depleted composition HT-Na1-xZn4-ySb3, stable in narrow temperature range. The hydride route yields single phase samples of both antimonides, allowing for the experimental access to their transport properties. The crystal structures, synthesis, structural transformations, and transport properties of the NaZn4Sb3 and HT-Na1-xZn4-ySb3 are discussed herein.

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Section: ■ Results and Discussionmentioning

confidence: 99%

“…Moreover, both compounds are lacking the peak in thermal conductivity at lower temperatures. Such a peak is typical for temperature dependence of thermal conductivity of crystalline insulating/semiconducting solids [68][69].…”

Section: Synthesis Of Ht-mentioning

confidence: 91%

From NaZn₄Sb₃ to HT-Na_1–xZn_4–ySb₃: Panoramic Hydride Synthesis, Structural Diversity, and Thermoelectric Properties

et al. 2019

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“…The geometrical arrangements of atoms in the various clathrate structure types permit rich chemical diversity: nearly half of the stable elements in the periodic table are now known to be clathrate forming. [17,360,[413][414][415][416][417][418]421] The remarkable chemical flexibility of these structure types is one of the reasons inorganic clathrates continue to be actively investigated for their potential as thermoelectric materials, with new compositions still being discovered at an impressive pace (Figure II.e.2a). This chemical flexibility also allows for a wide variation of electrical transport properties, with clathrates from good metals to semiconductors to semi-insulating materials prepared by adjusting the guest and framework constituents and content.…”

Section: Iie Clathratesmentioning

confidence: 99%

Thermoelectrics: From history, a window to the future

Beretta

Neophytou

Hodges

et al. 2019

Materials Science and Engineering: R: Reports

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409

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Thermoelectricity offers a sustainable path to recover and convert waste heat into readily available electric energy, and has been studied for more than two centuries. From the controversy between Galvani and Volta on the Animal Electricity, dating back to the end of the XVIII century and anticipating Seebeck's observations, the understanding of the physical mechanisms evolved along with the development of the technology. In the XIX century Ørsted clarified some of the earliest observations of the thermoelectric phenomenon and proposed the first thermoelectric pile, while it was only after the studies on thermodynamics by Thomson, and Rayleigh's suggestion to exploit the Seebeck effect for power generation, that a diverse set of thermoelectric generators was developed.From such pioneering endeavors, technology evolved from massive, and sometimes unreliable, thermopiles to very reliable devices for sophisticated niche applications in the XX century, when Radioisotope Thermoelectric Generators for space missions and nuclear batteries for cardiac pacemakers were introduced. While some of the materials adopted to realize the first thermoelectric generators are still investigated nowadays, novel concepts and improved understanding of materials growth, processing, and characterization developed during the last 30 years has provided new avenues for the enhancement of the thermoelectric conversion efficiency, for example through nanostructuration, and favored the development of new classes of thermoelectric materials. With

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“…45 Inorganic clathrates applications include: (i) Thermoelectricity, i.e., generating energy from waste heat, which is currently the most well studied application of inorganic clathrates. 46 (ii) Photovoltaics-Guest-free silicon and germanium clathrates are known to have wide quasi-direct band gaps. For the Type II structure, the band gap varies from 1.7 to 0.8 eV for silicon and germanium clathrate, respectively, therefore these materials are of interest for photovoltaic applications.…”

Section: Clathrate Developments-knowledge and Applicationmentioning

confidence: 99%

Inorganic and methane clathrates: Versatility of guest–host compounds for energy harvesting

Krishna

Koh

2015

MRS Energy & Sustainability

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Inorganic Clathrates for Thermoelectric Applications

Cited by 23 publications

References 125 publications

From NaZn₄Sb₃ to HT-Na_1–xZn_4–ySb₃: Panoramic Hydride Synthesis, Structural Diversity, and Thermoelectric Properties

From NaZn₄Sb₃ to HT-Na_1–xZn_4–ySb₃: Panoramic Hydride Synthesis, Structural Diversity, and Thermoelectric Properties

Thermoelectrics: From history, a window to the future

Inorganic and methane clathrates: Versatility of guest–host compounds for energy harvesting

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Inorganic Clathrates for Thermoelectric Applications

Cited by 23 publications

References 125 publications

From NaZn4Sb3 to HT-Na1–xZn4–ySb3: Panoramic Hydride Synthesis, Structural Diversity, and Thermoelectric Properties

From NaZn4Sb3 to HT-Na1–xZn4–ySb3: Panoramic Hydride Synthesis, Structural Diversity, and Thermoelectric Properties

Thermoelectrics: From history, a window to the future

Inorganic and methane clathrates: Versatility of guest–host compounds for energy harvesting

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Product

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From NaZn₄Sb₃ to HT-Na_1–xZn_4–ySb₃: Panoramic Hydride Synthesis, Structural Diversity, and Thermoelectric Properties

From NaZn₄Sb₃ to HT-Na_1–xZn_4–ySb₃: Panoramic Hydride Synthesis, Structural Diversity, and Thermoelectric Properties