Relationship between electronic and crystal structure in Cu–Ni–Co–Mn–O spinels

Kukuruznyak, Dmitry A.; Moyer, Jerome G.; Prowse, Michael S.; Nguyen, Nam; Rehr, J. J.; Ohuchi, Fumio S.

doi:10.1016/j.elspec.2005.06.013

Cited by 9 publications

(4 citation statements)

References 12 publications

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“…With respect to Co 2 Cu 1 [CO], besides the larger amounts of Cu + compared to the amounts of Cu 0 , a negative binding energy shift is observed for Cu + , with Cu 2p 3/2 and Cu 2p 1/2 binding energies located at 930.7 and 950.6 eV, respectively. This anomalous negative binding energy shift has been attributed to tetrahedral Cu + species in cubic spinel oxides . We are not able to challenge this interpretation on the basis of the available data.…”

Section: Resultsmentioning

confidence: 79%

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Higher Alcohols through CO Hydrogenation over CoCu Catalysts: Influence of Precursor Activation

2014

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Bimetallic CoCu model catalysts were investigated for the synthesis of higher alcohols using catalytic CO hydrogenation according to the Fischer−Tropsch technology. Emphasis was placed on revealing the influence of the activation conditions. Accordingly, catalyst precursors were activated in argon, hydrogen, syngas (CO/H 2 ), and CO under atmospheric conditions and at elevated temperatures (370 °C). All catalyst precursors were prepared via oxalate coprecipitation in the absence of a classic support. Alcohol selectivities between 30 and ∼40% (up to ∼50% for the sum of alcohols and alkenes) were obtained with an Anderson−Schulz−Flory (ASF) chain lengthening probability maximizing the slate up to C 6 . Detailed catalysis and characterization studies were performed using a Co 2 Cu 1 catalyst composition. The catalytic performances of the H 2 -and syngas-activated Co 2 Cu 1 catalyst were similar. While the CO-activated catalyst shows significantly higher catalytic activity and ASF chain lengthening probability, the alcohol selectivities are lower than those of H 2 -or syngas-activated ones. All catalysts required time on stream for several hours to achieve steady-state catalytic performance. Co 2 Cu 1 catalysts were characterized by temperature-programmed decomposition (TPDec), in situ N 2 physisorption (Brunauer−Emmett−Teller), transmission electron microscopy (TEM), and in situ X-ray photoelectron spectroscopy (XPS). The data indicate major restructuring occurs during activation. An "onion-like" graphitic carbon shell was observed via TEM for the CO-activated Co 2 Cu 1 catalyst, which probably originated mainly from the Boudouard reaction (2CO + [ ] ad → C ad + CO 2 ). This interpretation is in accordance with the TPDec profiles and XPS results. The latter also indicates that syngas and CO activation lead to higher than nominal Co/Cu surface ratios. The surface segregation of Co in the presence of CO atmospheres is interpreted on the basis of Co@Cu core−shell structured particles.

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Section: Resultsmentioning

confidence: 79%

“…This anomalous negative binding energy shift has been attributed to tetrahedral Cu + species in cubic spinel oxides. 16 We are not able to challenge this interpretation on the basis of the available data. Undoubtedly, this result calls for a more extensive spectroscopic investigation.…”

Section: Acs Catalysismentioning

confidence: 93%

Higher Alcohols through CO Hydrogenation over CoCu Catalysts: Influence of Precursor Activation

2014

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“…The Ta 4f spectra at points D and F of Figure a are split by 1.8 eV, and a small shift toward higher binding energy was observed rather than to lower binding energy as expected for a cation reduction. This kind of anomalous negative binding energy shift is not an uncommon phenomenon, although a physical explanation for this kind of behavior is not clear. − …”

Section: Resultsmentioning

confidence: 99%

Conditions for Ta^IV–Ta^IV Bonding in Trirutile Li_xMTa₂O₆

et al. 2015

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Stabilization of Ta-Ta bonding in an oxide across a shared octahedral-site edge of a Ta2 dimer is not known. Investigation of Li insertion into the trirutile structure of MTa2O6 with M = Mg, Cr, Fe, Co, and Ni indicates that Ta-Ta bonding across the shared octahedral-site edge of the dimer can be stabilized by a reversible electrochemical reduction of Ta(V) to Ta(IV) for M = Cr, Fe, Co, and Ni but not for M = Mg. Chemical reduction of MTa2O6 by n-butyl lithium only reduced NiTa2O6 to any significant extent. With M = Fe, Co, or Ni, electrochemical formation of the Ta-Ta bonds is accompanied by a partial reduction of the Fe(II), Co(II), or Ni(II) to Fe(0), Co(0), or Ni(0). For M = Cr, two Li per formula unit can be inserted reversibly with no displacement of Cr(0). For M = Mg, no Mg(II) are displaced by Li insertion, but a solid-electrolyte interphase (SEI) layer is formed on the oxide with no evidence of Ta-Ta bonding. Stabilization of Ta-Ta bonding across a shared octahedral-site edge in a dimer appears to require significant hybridization of the Ta(V) 5d(0) and M 4s(0) states.

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“…However, the low carrier concentration in Co 0.98 Mn 2.02 O 4 results in high resistivity [10,41], which limits its applications to the fields involving low-temperature measurements and suppression of inrush current. The extended X-ray absorption fine structure (EXAFS) results reveal that there is Cu + and Cu 2+ maintains the tetrahedral coordination in the Ni 0.48 Co 0.24 Cu 0.6 Mn 1.68 O 4 oxide [42]. Larger Cu + O 4 tetrahedrons make Mn 4+ O 6 octahedrons have cubic symmetry, while smaller Cu 2+ O 4 tetrahedrons make the Mn 3+ O 6 octahedrons have distorted tetragonal symmetry, which is induced by the oxidationreduction reaction Cu + + Mn 4+ → Cu 2+ + Mn 3+ at high temperatures.…”

Section: Introduction mentioning

confidence: 99%

Enhanced conductivity and stability of Co _0.98Cu _xMn _{2.02−
x}O ₄ ceramics with dual phases and twin structures

Ma¹,

He²,

Bi³

et al. 2023

Journal of Advanced Ceramics

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Semiconductor materials with heterogeneous interfaces and twin structures generally demonstrate a higher concentration of carriers and better electrical stability. A variety of Cu-doped Co 0.98 Cu x Mn 2.02−x O 4 (0 ≤ x ≤ 0.5) negative temperature coefficient (NTC) ceramics with dual phases and twin structures were successfully prepared in this study. Rietveld refinement indicates that the content of a cubic spinel phase increases with increasing Cu content. The addition of Cu can promote grain growth and densification. Atomic-level structural characterization reveals the evolution of twin morphology from large lamellae with internal fine lamellae (L IT lamellae) to large lamellae without internal fine lamellae (L lamellae) and the distribution of twin boundary defects. First-principles calculations reveal that the dual phases and twin structures have lower oxygen-vacancy formation energy than those in the case of the pure tetragonal and cubic spinel, thereby enhancing the transmission of carriers. Additionally, the three-dimensional charge-density difference shows that metal ions at the interface lose electrons and dwell in high valence states, thereby enhancing electrical stability of the NTC ceramics. Furthermore, the additional Cu ions engage in electron-exchange interactions with Mn and Co ions, thereby reducing resistivity. In comparison to previous Cu-containing systems, the Co 0.98 Cu x Mn 2.02−x O 4 series exhibit superior stability (aging value ≤ 2.84%), tunable room-temperature resistivity (ρ), and material constant (B) value (17.5 Ω•cm ≤ ρ ≤ 7325 Ω•cm, 2836 K ≤ B ≤ 4315 K). These discoveries lay a foundation for designing and developing new NTC ceramics with ultra-high performance.

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Relationship between electronic and crystal structure in Cu–Ni–Co–Mn–O spinels

Cited by 9 publications

References 12 publications

Higher Alcohols through CO Hydrogenation over CoCu Catalysts: Influence of Precursor Activation

Higher Alcohols through CO Hydrogenation over CoCu Catalysts: Influence of Precursor Activation

Conditions for Ta^IV–Ta^IV Bonding in Trirutile Li_xMTa₂O₆

Enhanced conductivity and stability of Co _0.98Cu _xMn _{2.02−
x}O ₄ ceramics with dual phases and twin structures

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Relationship between electronic and crystal structure in Cu–Ni–Co–Mn–O spinels

Cited by 9 publications

References 12 publications

Higher Alcohols through CO Hydrogenation over CoCu Catalysts: Influence of Precursor Activation

Higher Alcohols through CO Hydrogenation over CoCu Catalysts: Influence of Precursor Activation

Conditions for TaIV–TaIV Bonding in Trirutile LixMTa2O6

Enhanced conductivity and stability of Co 0.98Cu x Mn 2.02− x O 4 ceramics with dual phases and twin structures

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Product

Resources

About

Conditions for Ta^IV–Ta^IV Bonding in Trirutile Li_xMTa₂O₆

Enhanced conductivity and stability of Co _0.98Cu _xMn _{2.02−
x}O ₄ ceramics with dual phases and twin structures