Investigations on a New Copper Niobium Oxide of LiNb3O8 Type Using Chemical Analysis and X-Ray Powder Diffraction Profile Analysis.

Marinder, Bengt‐Olov; Werner, Per‐Erik; Wahlström, Ebba; Malmros, Gunnar; Sjöblom, Johan; Strand, T. G.; Sukhoverkhov, V. F.

doi:10.3891/acta.chem.scand.34a-0051

Cited by 30 publications

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“…As shown in Figure 4, in O2-Cu 4 Nb 8 O 23 the JT distorted octahedral coordination characteristic of Cu 2þ ions is absent in the Cu(2) and Cu(3) ions (those directly affected by the oxygen vacancy), where the distribution of distances corresponds to rather distorted polyhedra, as is not unusual in Cu þ compounds. 36,[38][39][40] The loss of JT distortion on Cu(2) is consistent with their reduction from Cu 2þ (JT active t 2g Finally, it is interesting to analyze the charge density reorganization upon reduction in the manganoculombite. As an example, Figure 7 shows the net electron spin density for O2-Mn 4 Nb 8 O 23 , where the oxygen vacancy affects two Mn and one Nb ions, compared to that of the initial Mn 4 Nb 8 O 24 .…”

Section: Resultsmentioning

confidence: 77%

First Principles Investigation of Oxygen Vacancies in Columbite MNb₂O₆ (M = Mn, Fe, Co, Ni, Cu)

2009

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This work presents a computational study on the stability and electronic properties of oxygen vacancies in candidate mixed electronic-ionic conducting columbites, MNb 2 O 6 (M = Mn, Fe, Co, Ni, Cu). Calculations are based on density functional theory with the DFTþU method. Three distinct oxygen vacancy types are investigated, differing by the coordination of the oxygen atoms removed: oxygen atoms coordinated by three, two, or one Nb ion. Calculation shows that the energy of oxygen vacancy formation depends on the transition metal ion, with values ranging from 6 eV in MnNb 2 O 6 to 3.5 eV in CuNb 2 O 6 (data refers to one oxygen vacancy per four formula units, or 4.16% vacancies). For a given transition metal the location of the vacancy formation energies on the different sites vary by a maximum range of 0.85 eV. In both MnNb 2 O 6 and CuNb 2 O 6 the oxygen vacancy formation induces (a) a narrowing of the band gap and (b) an electronic density redistribution leading to the reduction of cations to lower oxidation states. For MnNb 2 O 6 reduction affects mostly Nb 5þ ions, while for CuNb 2 O 6 the Cu 2þ ions are reduced to Cu 1þ . The potential improvement of electronic conductivity in CuNb 2 O 6-x together with the moderate vacancy formation energy makes this material a potential mixed electronic-ionic conductor.

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Section: Resultsmentioning

confidence: 77%

First Principles Investigation of Oxygen Vacancies in Columbite MNb₂O₆ (M = Mn, Fe, Co, Ni, Cu)

2009

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“…The CuNb 3 O 8 phase was initially found during phase composition studies in the copper− niobium−oxygen system and suggested to have copper deficiencies that made the stoichiometry closer to Cu 0.81 I Cu 0.17 II Nb 2.97 O 8 . 82 While the structure type is the same as that reported for LiNb 3 O 8 , there are significant differences in the Li and Cu positions that lead to the highly distorted tetrahedral coordination environment of the Cu(I) cations. Despite the distortion at the copper sites, the NbO 6 octahedra remain nearly identical between the two phases.…”

Section: Introductionmentioning

confidence: 75%

Copper(I)-Based p-Type Oxides for Photoelectrochemical and Photovoltaic Solar Energy Conversion

2016

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Recent research efforts have been growing into p-type copper(I) based oxides for development of their use in solar energy applications. The oxides of interest include the binary Cu2O and a number of new ternary Cu x M y O z oxides. Both the binary and ternary Cu(I)-based oxides have many advantages when compared to other well-known p-type oxides such as NiO, III–V, and II–VI semiconductors. The benefits found within the diverse group of Cu(I)-containing oxides include bandgap sizes that can be tuned from ∼1.2 to >3.0 eV, high charge carrier mobility, and favorable band energies relative to fuel-producing redox couples. These properties give them potential utility in a variety of different solar applications, such as in dye-sensitized solar cells and suspended powder photocatalysis. Research efforts into surface modifications and changes in their chemical compositions and structures have allowed for greater stability and greater efficiency in aqueous solutions, both of which have represented two key barriers for this class of materials. Presented in this review are the currently known binary and ternary Cu(I)-oxides and relationships of their syntheses and structures with their visible-light and ultraviolet bandgap sizes, band energies, and photoelectrochemical properties. As their constituent elements are relatively abundant and nontoxic, they represent an attractive class of materials that can be used in the conversion of sunlight to electricity or solar fuels.

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“…26,[28][29][30] However, even after long reaction times, the crystallinity of CuNbO 3 remained comparatively poor and coexisted with a secondary phase of CuNb 3 O 8 impurity. 24,29,30,[39][40][41] The structure of CuNbO 3 is ABO 3 lamellar-type, as shown in Fig. 2.…”

Section: Structural Characterizationmentioning

confidence: 96%

Screened coulomb hybrid DFT investigation of band gap and optical absorption predictions of CuVO₃, CuNbO₃ and Cu₅Ta₁₁O₃₀ materials

Harb

Masih

Takanabe

2014

Phys. Chem. Chem. Phys.

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We present a joint theoretical and experimental investigation of the optoelectronic properties of CuVO3, CuNbO3 and Cu5Ta11O30 materials for potential photocatalytic and solar cell applications. In addition to the experimental results obtained by powder X-ray diffraction and UV-Vis spectroscopy of the materials synthesized under flowing N2 gas at atmospheric pressure via solid-state reactions, the electronic structure and the UV-Vis optical absorption coefficient of these compounds are predicted with high accuracy using advanced first-principles quantum methods based on DFT (including the perturbation theory approach DFPT) within the screened coulomb hybrid HSE06 exchange-correlation formalism. The calculated density of states are found to be in agreement with the UV-Vis diffuse reflectance spectra, predicting a small indirect band gap of 1.4 eV for CuVO3, a direct band gap of 2.6 eV for CuNbO3, and an indirect (direct) band gap of 2.1 (2.6) eV for Cu5Ta11O30. It is confirmed that the Cu(I)-based multi-metal oxides possess a strong contribution of filled Cu(I) states in the valence band and of empty d(0) metal states in the conduction band. Interestingly, CuVO3 with its predicted small indirect band gap of 1.4 eV shows the highest absorption coefficient in the visible range with a broad absorption edge extending to 886 nm. This novel result offers a great opportunity for this material to be an excellent candidate for solar cell applications.

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Investigations on a New Copper Niobium Oxide of LiNb3O8 Type Using Chemical Analysis and X-Ray Powder Diffraction Profile Analysis.

Cited by 30 publications

References 0 publications

First Principles Investigation of Oxygen Vacancies in Columbite MNb₂O₆ (M = Mn, Fe, Co, Ni, Cu)

First Principles Investigation of Oxygen Vacancies in Columbite MNb₂O₆ (M = Mn, Fe, Co, Ni, Cu)

Copper(I)-Based p-Type Oxides for Photoelectrochemical and Photovoltaic Solar Energy Conversion

Screened coulomb hybrid DFT investigation of band gap and optical absorption predictions of CuVO₃, CuNbO₃ and Cu₅Ta₁₁O₃₀ materials

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Investigations on a New Copper Niobium Oxide of LiNb3O8 Type Using Chemical Analysis and X-Ray Powder Diffraction Profile Analysis.

Cited by 30 publications

References 0 publications

First Principles Investigation of Oxygen Vacancies in Columbite MNb2O6 (M = Mn, Fe, Co, Ni, Cu)

First Principles Investigation of Oxygen Vacancies in Columbite MNb2O6 (M = Mn, Fe, Co, Ni, Cu)

Copper(I)-Based p-Type Oxides for Photoelectrochemical and Photovoltaic Solar Energy Conversion

Screened coulomb hybrid DFT investigation of band gap and optical absorption predictions of CuVO3, CuNbO3 and Cu5Ta11O30 materials

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First Principles Investigation of Oxygen Vacancies in Columbite MNb₂O₆ (M = Mn, Fe, Co, Ni, Cu)

First Principles Investigation of Oxygen Vacancies in Columbite MNb₂O₆ (M = Mn, Fe, Co, Ni, Cu)

Screened coulomb hybrid DFT investigation of band gap and optical absorption predictions of CuVO₃, CuNbO₃ and Cu₅Ta₁₁O₃₀ materials