The oxidation states of elements in pure and Ca-doped BiCuSeO thermoelectric oxides

Hsiao, Chun Lung; Qi, Xiaoding

doi:10.1016/j.actamat.2015.08.079

Cited by 38 publications

(22 citation statements)

References 36 publications

(38 reference statements)

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“…Figure 3a exhibits two main peaks at the binding energy of 159.1 and 164.4 eV, corresponding to the core lines of 4f 7/2 and 4f 5/2 of Bi 3+ ions, respectively. The binding energy difference between these two peaks is about 5.3 eV, which is in good agreement with the previously data obtained from the Pb or Ca-doped BiCuSeO bulk samples [10, 33]. Moreover, additional shoulder peaks located at the lower binding energy side of the Bi 3+ peak are observed in Fig.…”

Section: Resultssupporting

confidence: 91%

“…Moreover, additional shoulder peaks located at the lower binding energy side of the Bi 3+ peak are observed in Fig. 3a, indicating that there exist some Bi ions with lower oxidation state of + 3 − x in the Ba-doped film sample [10, 33]. These Bi ions with lower valence state can contribute holes to Cu-Se layer, thus increasing the carrier concentration and improving the electrical conductivity.…”

Section: Resultsmentioning

confidence: 99%

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Enhanced Thermoelectric Performance of c-Axis-Oriented Epitaxial Ba-Doped BiCuSeO Thin Films

et al. 2018

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We reported the epitaxial growth of c-axis-oriented Bi1−xBaxCuSeO (0 ≤ x ≤ 10%) thin films and investigated the effect of Ba doping on the structure, valence state of elements, and thermoelectric properties of the films. X-ray photoelectron spectroscopy analysis reveal that Bi3+ is partially reduced to the lower valence state after Ba doping, while Cu and Se ions still exist as + 1 and − 2 valence state, respectively. As the Ba doping content increases, both resistivity and Seebeck coefficient decrease because of the increased hole carrier concentration. A large power factor, as high as 1.24 mWm−1 K−2 at 673 K, has been achieved in the 7.5% Ba-doped BiCuSeO thin film, which is 1.5 times higher than those reported for the corresponding bulk samples. Considering that the nanoscale-thick Ba-doped films should have a very low thermal conductivity, high ZT can be expected in the films.Electronic supplementary materialThe online version of this article (10.1186/s11671-018-2752-6) contains supplementary material, which is available to authorized users.

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Section: Resultssupporting

confidence: 91%

Section: Resultsmentioning

confidence: 99%

Enhanced Thermoelectric Performance of c-Axis-Oriented Epitaxial Ba-Doped BiCuSeO Thin Films

et al. 2018

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“…The peak can be separated by two Gaussian peaks, which may come from the difference of the element bonded to Se. 25,26 The ideal oxidation states of the elements in BiCuSeO have been assumed to be Bi 3þ , Cu 1þ , Se 2 , À and O 2À , based on the requirement of the overall charge neutrality. 19,27 Apparently, BiCuSeO is not a typical ionic compound and the oxidation state of each element must not be so explicitly defined.…”

Section: Xps Results and Proposed Charge Valence Equationsmentioning

confidence: 99%

“…The increase in the Cu 2þ was also confirmed for the Ca-doped BiCuSeO, in which hole carriers were introduced and the q(T) decreased with increasing Ca doping. 26 The change of the Cu oxidation state from þ1 to þ2 introduces donors and donates electrons to the conduction band minimum, which may compensate the hole carriers. However, the decrease in q(T) in Fig.…”

Section: Xps Results and Proposed Charge Valence Equationsmentioning

confidence: 99%

Oxidation states and thermoelectric properties of BiCuSeO bulks fabricated under Bi or Se deficiencies in the nominal composition

Ishizawa

Yasuzato

Fujishiro

et al. 2018

Journal of Applied Physics

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We have fabricated the BiCuSeO bulks using raw materials with Bi or Se deficiencies in the nominal composition and investigated crystallographic, chemical compositional, and thermoelectric properties. Owing to the Bi or Se deficiencies in the starting composition, excessive elements and related compounds were deposited as impurity phases and the matrix phase is nearly the stoichiometric BiCuSeO phase. The electrical resistivity, q(T), of the bulks decreases and thermoelectric power, S(T), also decreases with increasing the contents of Bi or Se deficiencies in the starting composition in spite of the stoichiometric matrix phase. These results strongly suggest that, from the X-ray photoelectron spectroscopy measurements, the actual oxidation states of Bi and Cu deviate from the formal valences of stoichiometric Bi 3þ Cu 1þ Se 2À O 2À . The introduction of a small amount of Bi and Se vacancies is also suggested. As a result, mobile carriers are introduced and the q and S values are changed. The maximum thermoelectric dimensionless figure of merit of ZT ¼ 0.60 was achieved at 773 K for the Bi 1-x CuSeO samples (x ¼ 0.025 and 0.05) in the starting composition. These results are in clear contrast with the reported results for the Cu deficiency bulks. Using these results, we propose charge valence equations and the origin of the carriers in the present BiCuSeO bulks and discuss the influence of created carriers on the thermoelectric properties.Published by AIP Publishing. https://doi.

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“…Apart from various attempts to enhance thermoelectric performance mentioned above, the interested readers are encouraged to refer to these extensive works that have been done on BiCuSeO systems, such as ultrathin BiCuSeO nanosheets [47], elastic and thermal properties [48,49], phonon transport [50,51], oxidation states [52], Cu vacancies [53,54], thermal stability [55,56], and the TEM study on BiCuSO and BiCuSeO that shows that Cu deficiency also plays a role in the stability and properties of those layered oxychalcogenides [54]. All of these studies largely enrich the understanding of BiCuSeO systems and have a great sense for future research.…”

Section: A Short Review For Various Attempts To Optimize Bicuseo Smentioning

confidence: 99%

BiCuSeO Thermoelectrics: An Update on Recent Progress and Perspective

et al. 2017

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A BiCuSeO system has been reported as a promising thermoelectric material and has attracted great attention in the thermoelectric community since 2010. Recently, several remarkable studies have been reported and the ZT of BiCuSeO was pushed to a higher level. It motivates us to systematically summarize the recent reports on the BiCuSeO system. In this short review, we start with several attempts to optimize thermoelectric properties of BiCuSeO. Then, we introduce several opinions to explore the origins of low thermal conductivity for BiCuSeO. Several approaches to enhance thermoelectric performance are also summarized, including modulation doping, introducing dual-vacancies, and dual-doping, etc. At last, we propose some possible strategies for enhancing thermoelectric performance of BiCuSeO in future research.

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The oxidation states of elements in pure and Ca-doped BiCuSeO thermoelectric oxides

Cited by 38 publications

References 36 publications

Enhanced Thermoelectric Performance of c-Axis-Oriented Epitaxial Ba-Doped BiCuSeO Thin Films

Enhanced Thermoelectric Performance of c-Axis-Oriented Epitaxial Ba-Doped BiCuSeO Thin Films

Oxidation states and thermoelectric properties of BiCuSeO bulks fabricated under Bi or Se deficiencies in the nominal composition

BiCuSeO Thermoelectrics: An Update on Recent Progress and Perspective

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