Raman scattering study of the high temperature phase transitions of NaTaO3

Teixeira, Nayara Gomes; Dias, Anderson; Moreira, R. L.

doi:10.1016/j.jeurceramsoc.2007.02.015

Cited by 24 publications

(20 citation statements)

References 19 publications

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“…Nevertheless, no trace of emission peak was observed for surface-doped sample. It is well accepted that the 5 D 0 − 7 F 0 transition is highly directed by local symmetry of cationic sites in the orthorhombic structure of NaTaO 3 that have C 1 site symmetry for Ta ions and C s site symmetry for Na ions, 35 for which the 5 D 0 − 7 F 0 transition of Eu 3+ is allowed. Having this in mind, it is possible to specify the site-selective occupation of Eu 3+ ions as a function of Na/Ta molar ratio.…”

Section: Resultsmentioning

confidence: 99%

Tunable Optical and Photocatalytic Performance Promoted by Nonstoichiometric Control and Site-Selective Codoping of Trivalent Ions in NaTaO₃

Peng

Guo

et al. 2014

J. Phys. Chem. C

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The present work explores a solid state route to synthesis of trivalent ions (Eu 3+ , La 3+ , etc.) doped NaTaO 3 with controlled nonstoichiometric chemistry and lattice parameters with an aim to exploring electronic structure and photocatalytic performance. All samples were fully characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic absorption spectrophotometry, UV− vis diffuse reflectance spectroscopy, and photoluminescence measurement. By employing Eu 3+ as a model trivalent ion doped in NaTaO 3 lattice, the effects of siteselective doping and nonstoichiometric chemistry on the lattice parameters, band gap structure, photocatalytic activity toward methylene blue solution, and photocatalytic hydrogen evolution were systematically investigated. A nonstoichiometric Na/Ta molar ratio led to site-selective occupation of Eu 3+ ions which was changed from sole substitution to dual substitutions. Meanwhile, the nonstoichiometric Na/Ta molar ratio and site-selective occupation of Eu 3+ resulted in a monotonous lattice expansion and local symmetry distortion. Lattice variation, doping effects, and its relevant defect chemistry had a great impact on the ν 3 mode vibration of the O−Ta bond, which became asymmetric and shifted toward higher wavenumbers. Moreover, contrary to theoretical predictions, Eu 3+ -doped NaTaO 3 nanocrystals showed an abnormal narrowing of the band gap energies and weak visible light absorption with variation of Na/Ta molar ratios, which is thought to be related to doping effects, defect chemistry, and variation of lattice parameters. With well-defined lattice structure and defect centers and electronic structure via nonstoichiometric control and trivalent ions doping, the photocatalytic activity of trivalent ions-doped NaTaO 3 can be well regulated and optimized.

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Section: Resultsmentioning

confidence: 99%

Tunable Optical and Photocatalytic Performance Promoted by Nonstoichiometric Control and Site-Selective Codoping of Trivalent Ions in NaTaO₃

Peng

Guo

et al. 2014

J. Phys. Chem. C

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“…The Na cation is surrounded by 12 O anions in a dodecahedral environment, the Ta cation is octahedrally coordinated by six O ions, and the O anions are coordinated by two Ta cations and four Na cations. There is presence of structural phase transitions with temperature for NaTaO 3 , and the ideal cubic phase can be observed only at temperatures above 600°C 37–44 . On the other hand, other different crystal structures, as a result of distorting the 3D framework of the linked TaO 6 octahedra, are generally observed at room temperature.…”

Section: Introductionmentioning

confidence: 98%

“…There is presence of structural phase transitions with temperature for NaTaO 3 , and the ideal cubic phase can be observed only at temperatures above 6001C. [37][38][39][40][41][42][43][44] On the other hand, other different crystal structures, as a result of distorting the 3D framework of the linked TaO 6 octahedra, are generally observed at room temperature.…”

Section: Introductionmentioning

confidence: 99%

Structure Characterization and Tuning of Perovskite‐Like NaTaO₃ for Applications in Photoluminescence and Photocatalysis

Tsai

Teng

2009

Journal of the American Ceramic Society

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Perovskite‐like NaTaO3 powders have potential applications in photoluminescence and photocatalysis. Sol–gel, hydrothermal and solid‐state methods were used to synthesize NaTaO3 powders of different crystalline structures, which were identified by Rietveld refinement simulation of X‐ray diffraction patterns and transmission electron microscopic diffraction. The refinement results show that the sol–gel specimen has a monoclinic phase with a Ta−O−Ta bond angle of 179° while the hydrothermal and solid‐state specimens have an orthorhombic phase with bond angles of 163° and 157°, respectively. By excitation with a 304 nm light source, these NaTaO3 specimens show photoluminescence emission at ca. 450 nm. The photoluminescence intensity of the specimens had an order solid state >hydrothermal >sol–gel, which is opposite to that of the Ta−O−Ta bond angle. On the other hand, the photocatalytic activity of the NaTaO3 specimens in water splitting showed the same order as that of the Ta−O−Ta bond angle. This paper directly evidenced that the Ta−O−Ta bond angle affects the separation rate of the photo‐induced charges, as well as that structure tuning of tantalates is achievable and crucial for applications in photoluminescence and photocatalysis.

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“…We detected the main Raman band at 620 cm –1 , corresponding to the lattice vibrations of the NaO 12 cuboctahedra in NaTaO 3 (Figure ). Upon doping NaTaO 3 with Ba 2+ , additional Raman bands were detected at ∼830 cm –1 . The 830 cm –1 Raman band originated from the breathing vibrations of BO 6 octahedra in B-site substituted perovskites, AB 1– x B′ x O 3 . , In an ideal cubic perovskite ABO 3 , the BO 6 breathing mode with A 1g symmetry does not contribute to Raman scattering due to symmetry restriction.…”

Section: Resultsmentioning

confidence: 99%

Dependence of Photoexcited Electron Behavior on Octahedral Distortion in Barium-Doped NaTaO₃ Photocatalysts

et al. 2021

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This study aims to investigate the behavior of photoexcited electrons in intentionally distorted Ba-doped NaTaO3 photocatalysts with time-resolved microwave conductivity and steady-state IR absorption induced by UV light. As probed by X-ray absorption fine structure and Raman spectroscopies, doping NaTaO3 with Ba2+ produces structural nonperiodicity and distorts the octahedral sublattice, proposedly resulting in the formation of electron traps. A higher density of shallow electron traps is suggested to be responsible for the longer electron lifetime and larger electron population, because shallowly trapped electrons are less likely to recombine with holes. The half-lifetime of photoexcited electrons is considerably long, even longer than 0.8 ms in the Ba-doped NaTaO3 sample with moderate distortion. The population of photoexcited electrons under Hg–Xe lamp irradiation increases by 32 times in this sample compared to that in undoped NaTaO3, generating H2/O2 mixtures with the rates of 385 μmol h–1 (H2) and 180 μmol h–1 (O2) when irradiated with a Hg lamp in the absence of cocatalyst and sacrificial compound. Moderate distortion seems favorable to produce shallow electron traps in comparison to large and small distortions, leading to the highest water splitting rate. The orders of photocatalysts based on their electron lifetime, electron population, and water splitting rate are identical, indicating that the photoexcited electrons worked in the water splitting reactions.

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Raman scattering study of the high temperature phase transitions of NaTaO3

Cited by 24 publications

References 19 publications

Tunable Optical and Photocatalytic Performance Promoted by Nonstoichiometric Control and Site-Selective Codoping of Trivalent Ions in NaTaO₃

Tunable Optical and Photocatalytic Performance Promoted by Nonstoichiometric Control and Site-Selective Codoping of Trivalent Ions in NaTaO₃

Structure Characterization and Tuning of Perovskite‐Like NaTaO₃ for Applications in Photoluminescence and Photocatalysis

Dependence of Photoexcited Electron Behavior on Octahedral Distortion in Barium-Doped NaTaO₃ Photocatalysts

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Raman scattering study of the high temperature phase transitions of NaTaO3

Cited by 24 publications

References 19 publications

Tunable Optical and Photocatalytic Performance Promoted by Nonstoichiometric Control and Site-Selective Codoping of Trivalent Ions in NaTaO3

Tunable Optical and Photocatalytic Performance Promoted by Nonstoichiometric Control and Site-Selective Codoping of Trivalent Ions in NaTaO3

Structure Characterization and Tuning of Perovskite‐Like NaTaO3 for Applications in Photoluminescence and Photocatalysis

Dependence of Photoexcited Electron Behavior on Octahedral Distortion in Barium-Doped NaTaO3 Photocatalysts

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Tunable Optical and Photocatalytic Performance Promoted by Nonstoichiometric Control and Site-Selective Codoping of Trivalent Ions in NaTaO₃

Tunable Optical and Photocatalytic Performance Promoted by Nonstoichiometric Control and Site-Selective Codoping of Trivalent Ions in NaTaO₃

Structure Characterization and Tuning of Perovskite‐Like NaTaO₃ for Applications in Photoluminescence and Photocatalysis

Dependence of Photoexcited Electron Behavior on Octahedral Distortion in Barium-Doped NaTaO₃ Photocatalysts