Semiconducting Ge clathrates: Promising candidates for thermoelectric applications

Nolas, George S.; Cohn, J. L.; Slack, Glen A.; Schujman, Sandra

doi:10.1063/1.121747

Cited by 921 publications

(684 citation statements)

References 13 publications

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“…800 K for the composition Zr 0. 5 Since most of the current work on half-Heusler is focused on isoelectronic alloying, it is reasonable to anticipate that there is considerable room for further improvement in ZT through the use of various nanostructures. Systematic theoretical calculations on 36 kinds of half-Heusler compounds by Yang et al [75], demonstrates that there are potential new half-Heusler compounds beyond the well-studied n-type MNiSn (LaPdBi, NdCoSn, ZrCoBi, etc.)…”

Section: Review Articlementioning

confidence: 99%

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High-performance nanostructured thermoelectric materials

et al. 2010

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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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Section: Review Articlementioning

confidence: 99%

“…Th e search for new materials, such as skutterudites [3,4] and clathrates [5], is mainly motivated by the suggestion of Slack [6]. In those compounds, the 'rattling' motion of loosely bonded atoms within a large cage generates strong scattering against lattice phonon propagation, but has less of an impact on the transport of electrons.…”

Section: Review Articlementioning

confidence: 99%

High-performance nanostructured thermoelectric materials

et al. 2010

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“…Intermetallic clathrate-I compounds have been identified [1,2] as a promising class of candidate thermoelectric materials. The enhanced thermoelectric properties in these materials arise in large part from marked guest-host interactions.…”

Section: Introductionmentioning

confidence: 99%

A study of low-energy guest phonon modes in clathrate-II Na_xSi₁₃₆(x= 3, 23, and 24)

Beekman

Hermann

Möchel

et al. 2010

J. Phys.: Condens. Matter

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Single-crystal x-ray diffraction from clathrate-II Na x Si 136 (x = 24) prepared by a new technique reveals the exceptionally large Na@Si 28 atomic displacement parameter (U eq ) is strongly temperature dependent, and can be attributed to low-energy rattling modes associated with the Na guest. Inelastic neutron scattering (INS) spectra collected from Na x Si 136 powder specimens (x = 3, 23) confirm the presence of low-energy guest-derived phonon modes for Na@Si 28 and Na@Si 20 . The lower energy Na@Si 28 rattler mode falls in the frequency range of the silicon host acoustic phonons, indicating the possibility for interaction with these phonons. The presence of these low-energy modes combined with the ability to controllably vary the guest content presents a unique opportunity for exploring the influence of guest-framework interactions on the lattice dynamics in intermetallic clathrates.

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“…Studies on Ge and Sn clathrates gave rise to narrow gap semiconducting materials with compositions like K 8 Ge 44 or Rb 8 Sn 44 , where the metal oxidation is compensated by formation of vacancies in the clathrate framework. Compound clathrates such as Sr 8 Ga 16 Ge 30 have fully occupied frameworks and achieve charge balance by introduction of group 13 elements. Metal-deficient clathrates such as K 7 Si 46 are also known.…”

Section: Introductionmentioning

confidence: 99%

“…Sharp peaks near the Fermi level in the electronic density of states result in large Seebeck coefficients and also superconductivity for Ba-containing members. 3,4,[16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] Two main structural types were described during the initial studies of Si and Ge clathrate materials. [1][2][3][4][5][6][7][8][9] The type I clathrate has a primitive cubic structure (Pm3n: a o ~ 10.2 Å) based on dodecahedral [5 12 ] and tetrakaidecahedral [5 12 6 2 ] cages that are occupied by metal guest atoms to produce metallic Na 8 Si 46 whose formation is studied here.…”

Section: Introductionmentioning

confidence: 99%

Time-Resolved in Situ Synchrotron X-ray Diffraction Studies of Type 1 Silicon Clathrate Formation

et al. 2011

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Silicon clathrates are unusual open-framework solids formed by tetrahedrally-bonded silicon that show remarkable electronic and thermal properties. The type I structure has a primitive cubic unit cell containing cages occupied by metal atoms to give compositions such as Na 8 Si 46 or Na 2 Ba 6 Si 46 . Although their structure and properties are well described there is little understanding of the formation mechanism. Na 8 Si 46 is typically produced by metastable thermal decomposition under vacuum conditions from NaSi, itself an unusual structure containing Si 4 4-poly-anions. In this study we used in situ synchrotron X-ray diffraction combined with rapid X-ray detection on samples taken through a controlled temperature ramp (25-500 o C at 8 o /min) under vacuum conditions (10 -4 bar), to study the clathrate formation reaction. We also carried out complementary in situ high temperature solid state 23 Na NMR experiments using a sealed tube loaded under inert gas atmosphere conditions. We find no evidence for an intermediate amorphous phase during clathrate formation. Instead we observe an unexpectedly high degree of structural coherency between the Na 8 Si 46 clathrate and its NaSi precursor, evidenced by a smooth passage of several X-ray reflections from one structure into the other. The results indicate the possibility of an unusual, epitaxial-like, growth of the clathrate phase as Na atoms are removed from the NaSi precursor into the vacuum.

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Semiconducting Ge clathrates: Promising candidates for thermoelectric applications

Cited by 921 publications

References 13 publications

High-performance nanostructured thermoelectric materials

High-performance nanostructured thermoelectric materials

A study of low-energy guest phonon modes in clathrate-II Na_xSi₁₃₆(x= 3, 23, and 24)

Time-Resolved in Situ Synchrotron X-ray Diffraction Studies of Type 1 Silicon Clathrate Formation

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Semiconducting Ge clathrates: Promising candidates for thermoelectric applications

Cited by 921 publications

References 13 publications

High-performance nanostructured thermoelectric materials

High-performance nanostructured thermoelectric materials

A study of low-energy guest phonon modes in clathrate-II NaxSi136(x= 3, 23, and 24)

Time-Resolved in Situ Synchrotron X-ray Diffraction Studies of Type 1 Silicon Clathrate Formation

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A study of low-energy guest phonon modes in clathrate-II Na_xSi₁₃₆(x= 3, 23, and 24)