Thermoelectric properties of molybdenum oxides LnMo8O14 (Ln = La, Ce, Pr, Nd and Sm)

Xu, Jianxiao; Sonne, Monica; Pryds, Nini; Kleinke, Holger

doi:10.1016/j.jallcom.2009.09.136

Cited by 7 publications

(5 citation statements)

References 39 publications

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“…13a shows the TPFs of the four composites at different temperatures. It is seen that NdMo8O18 exhibits a peak TPF and ZT of 177 μW/m.K 2 and 0.1, respectively, at 1000 K. The κ of the composite has been reported to be 3.19 W/m.K at 322 K, which drops to 2 W/m.K at 1164 K [308,309]. It is evident that the TPF is certainly large enough to make these molybdenum oxide composites promising for high temperature energy scavenging applications.…”

Section: Te Properties Of Non-stoichiometric Doped and Composite Moo Xmentioning

confidence: 99%

Transition metal oxides – Thermoelectric properties

Walia

Balendhran

Nili

et al. 2013

Progress in Materials Science

329

199

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Transition metal oxides (TMOs) are a fascinating class of materials due to their wide ranging electronic, chemical and mechanical properties. Additionally, they are gaining increasing attention for their thermoelectric (TE) properties due to their high temperature stability, tunable electronic and phonon transport properties and well established synthesis techniques. In this article, we review TE TMOs at cryogenic, ambient and high temperatures. An overview of strategies used for morphological, composting and stoichiometric tuning of their key TE parameters is presented. This article also provides an outlook on the current and future prospects of implementing TMOs for a wide range of TE applications.

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Section: Te Properties Of Non-stoichiometric Doped and Composite Moo Xmentioning

confidence: 99%

Transition metal oxides – Thermoelectric properties

Walia

Balendhran

Nili

et al. 2013

Progress in Materials Science

329

199

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“…1 While ligand field theory generally provides a good framework for understanding the electronic states of transition metal oxides, 2 we are broadly interested in a special subset of transitional metal oxide compounds which contain direct metal−metal (M−M) bonds that have the potential to introduce radical changes in the electronic structure of oxides that may lead to enhanced functionality. Direct M−M bonds are most commonly found in early 4d and 5d transition metals (with M = Mo, Re, or Ru) that have a small number of electrons in d-orbitals (d 1 −d 4 ). Some examples include the compounds LnMo 8 O 14 (Ln = La, Ce, Pr, Nd, Sm), 3,4 LnMo 5 O 8 (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd), 5 Nd 4 Re 2 O 11 , 6 Ln 4 Re 6 O 19 (Ln = La, Pr, Nd), 7 and La 4 Ru 6 O 19 .…”

Section: ■ Introductionmentioning

confidence: 99%

“…Direct M–M bonds are most commonly found in early 4d and 5d transition metals (with M = Mo, Re, or Ru) that have a small number of electrons in d-orbitals (d 1 –d 4 ). Some examples include the compounds LnMo 8 O 14 (Ln = La, Ce, Pr, Nd, Sm), , LnMo 5 O 8 (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd), Nd 4 Re 2 O 11 , Ln 4 Re 6 O 19 (Ln = La, Pr, Nd), and La 4 Ru 6 O 19 . , The clearest signature of direct M–M bonds is the short distances between the metal participating in the bonding, as these bond lengths are far shorter than the M–M distances that are typically seen for the same compounds in the absence of M–M bonding (>3 Å). The shortest M–M bond distance reported is a Cr–Cr bond, 1.8028(9) Å, found in a molecular dinuclear chromium diazadiene complex .…”

Section: Introductionmentioning

confidence: 99%

Charge Disproportionation in Tetragonal La₂MoO₅, a Small Band Gap Semiconductor Influenced by Direct Mo–Mo Bonding

Colabello

Huq

Hybertsen³

et al. 2015

J. Am. Chem. Soc.

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The structure of the novel compound La2MoO5 has been solved from powder X-ray and neutron diffraction data and belongs to the tetragonal space group P4/m (no. 83) with a = 12.6847(3) Å and c = 6.0568(2) Å and with Z = 8. It consists of equal proportions of bioctahedral (Mo2O10) and square prismatic (Mo2O8) dimers, both of which contain direct Mo-Mo bonds and are arranged in 1D chains. The Mo-Mo bond length in the Mo2O10 dimers is 2.684(8) Å, while there are two types of Mo2O8 dimers with Mo-Mo bonds lengths of 2.22(2) and 2.28(2) Å. Although the average Mo oxidation state in La2MoO5 is 4+, the very different Mo-Mo distances reflect the fact that the Mo2O10 dimers contain only Mo(5+) (d(1)), while the prismatic Mo2O8 dimers only contain Mo(3+) (d(3)), a result directly confirmed by density function theory calculations. This is due to the complete disproportionation of Mo(4+), a phenomenon which has not previously been observed in solid-state compounds. La2MoO5 is diamagnetic, behavior which is not expected for a nonmetallic transition-metal oxide whose cation sites have an odd number of d-electrons. The resistivity displays the Arrhenius-type activated behavior expected for a semiconductor with a band gap of 0.5 eV, exhibiting an unusually small transport gap relative to other diamagnetic oxides. Diffuse reflectance studies indicate that La2MoO5 is a rare example of a stable oxide semiconductor with strong infrared absorbance. It is shown that the d-orbital splitting associated with the Mo2O8 and Mo2O10 dimeric units can be rationalized using simple molecular orbital bonding concepts.

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“…Compounds with direct metal–metal bonding form a very small but interesting subset of transition-metal oxides due to the unusual electronic states that result from the metal–metal bonding. − Analyses of the electronic structures of this class of compounds has shown that the degeneracy of the d -orbital derived states can be mostly or completely lifted as a consequence of the metal–metal bonding and that the resulting electronic states have a very sharp and narrow density of states that is more commonly associated with f -electron states . These systems offer the potential for generating interesting and potentially technologically relevant physical properties, as f -electrons may exhibit unusual behavior, including heavy Fermion transport and superconductivity associated with these heavy electrons.…”

Section: Introductionmentioning

confidence: 99%

Observation of Vacancies, Faults, and Superstructures in Ln₅Mo₂O₁₂ (Ln = La, Y, and Lu) Compounds with Direct Mo–Mo Bonding

et al. 2017

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Among oxide compounds with direct metal-metal bonding, the YMoO (ABO) structural family of compounds has a particularly intriguing low-dimensional structure due to the presence of bioctahedral BO dimers arranged in one-dimensional edge-sharing chains along the direction of the metal-metal bonds. Furthermore, these compounds can have a local magnetic moment due to the noninteger oxidation state (+4.5) of the transition metal, in contrast to the conspicuous lack of a local moment that is commonly observed when oxide compounds with direct metal-metal bonding have integer oxidation states resulting from the lifting of orbital degeneracy typically induced by the metal-metal bonding. Although a monoclinic C2/m structure has been previously proposed for LnMoO (Ln = La-Lu and Y) members of this family based on prior single crystal diffraction data, it is found that this structural model misses many important structural features. On the basis of synchrotron powder diffraction data, it is shown that the C2/m monoclinic unit cell represents a superstructure relative to a previously unrecognized orthorhombic Immm subcell and that the superstructure derives from the ordering of interchangeable MoO and LaO building blocks. The superstructure for this reason is typically highly faulted, as evidenced by the increased breadth of superstructure diffraction peaks associated with a coherence length of 1-2 nm in the c* direction. Finally, it is shown that oxygen vacancies can occur when Ln = La, producing an oxygen deficient stoichiometry of LaMoO and an approximately 10-fold reduction in the number of unpaired electrons due to the reduction of the average Mo valence from +4.5 to +4.05, a result confirmed by magnetic susceptibility measurements. This represents the first observation of oxygen vacancies in this family of compounds and provides an important means of continuously tuning the magnetic interactions within the one-dimensional octahedral chains of this system.

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Thermoelectric properties of molybdenum oxides LnMo8O14 (Ln = La, Ce, Pr, Nd and Sm)

Cited by 7 publications

References 39 publications

Transition metal oxides – Thermoelectric properties

Transition metal oxides – Thermoelectric properties

Charge Disproportionation in Tetragonal La₂MoO₅, a Small Band Gap Semiconductor Influenced by Direct Mo–Mo Bonding

Observation of Vacancies, Faults, and Superstructures in Ln₅Mo₂O₁₂ (Ln = La, Y, and Lu) Compounds with Direct Mo–Mo Bonding

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Thermoelectric properties of molybdenum oxides LnMo8O14 (Ln = La, Ce, Pr, Nd and Sm)

Cited by 7 publications

References 39 publications

Transition metal oxides – Thermoelectric properties

Transition metal oxides – Thermoelectric properties

Charge Disproportionation in Tetragonal La2MoO5, a Small Band Gap Semiconductor Influenced by Direct Mo–Mo Bonding

Observation of Vacancies, Faults, and Superstructures in Ln5Mo2O12 (Ln = La, Y, and Lu) Compounds with Direct Mo–Mo Bonding

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Charge Disproportionation in Tetragonal La₂MoO₅, a Small Band Gap Semiconductor Influenced by Direct Mo–Mo Bonding

Observation of Vacancies, Faults, and Superstructures in Ln₅Mo₂O₁₂ (Ln = La, Y, and Lu) Compounds with Direct Mo–Mo Bonding