Infrared spectra of some niobium minerals

Pilipenko, A.T.; Shevchenko, L. L.; Patselyuk, V. A.

doi:10.1007/bf00616116

Cited by 3 publications

(3 citation statements)

References 6 publications

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“…The relative position of this absorption band in the spectrum depends on the Ti vs. Nb ratio of the mineral. Splitting of the (Yi,Nb)O6 band commonly observed in the infrared spectra of low-symmetry perovskitetype compounds (Pilipenko et al, 1971;Sych et al, 1973) is not observed in our spectra ( Fig. 2a, b).…”

Section: Phase Relationshipscontrasting

confidence: 44%

“…Both spectra show a broad absorption band at 650-900 cm -1. This band corresponds to bond vibrations in the octahedral complexes (Ti,Nb)O6 and is typical of various perovskiteand pyrochlore-group minerals (Kostyleva-Labuntsova et al, 1978b;Pilipenko et al, 1971) and their synthetic analogues (Nyquist and Kagel, 1971;Sych et al, 1973). The relative position of this absorption band in the spectrum depends on the Ti vs. Nb ratio of the mineral.…”

Section: Phase Relationshipsmentioning

confidence: 93%

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Th-rich loparite from the Khibina alkaline complex, Kola Peninsula: isomorphism and paragenesis

Mitchell

Chakhmouradian

1998

Mineral. mag.

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Th-rich (up to 18.4 wt.% ThO 2 ) loparite occurs as an accessory phase in foyaite pegmatites at Mt. Eveslogchorr, Khibina complex, Russia. It is associated with aegirine, astrophyllite, eudialyte, lorenzenite, lamprophyllite, magnesio-arfvedsonit e and gerasimovskite. Loparite crystals are zoned from niobian loparite (core) to niobian thorian and thorian niobian loparite (rim). Th-enrichment is accompanied by a decrease in Na, LREE, Sr and increase in A-site vacancies. The most Th-rich composition approaches (Na 0.39 LREE 0.19 Th 0.12 Ca 0.05 Sr 0.02 ) S0.77 (Ti 0.76 Nb 0.27 ) S1.03 O 3 . The mineral is partly or completely metamict and after annealing gives an X-ray diffraction powder pattern similar to that of synthetic NaLaTi 2 O 6 and naturally occurring loparite of different composition. For the Th-rich rim sample, the five strongest diffraction lines (A Ê ) are: 2.72 (100) 110, 1.575 (60) 211, 1.925 (40), 1.368 (30) 220, 1.222 (20) 310; a = 3.867(2) A Ê . The X-ray diffraction patterns do not exhibit peak splitting or other diffraction lines typical of low-symmetry and ordered perovskite-type structures. Composition determinations, infrared transmission spectroscopy and X-ray diffractometry show that thorian loparite is partly replaced by betafite with LREE and Th as dominant A-site cations ('ceriobetafite'). Some loparite samples also exhibit thin replacement mantles of belyankinite with high LREE 2 O 3 and ThO 2 contents. Both 'ceriobetafite' and belyankinite were formed due to metasomatic alteration of loparite.

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Section: Phase Relationshipscontrasting

confidence: 44%

Section: Phase Relationshipsmentioning

confidence: 93%

Th-rich loparite from the Khibina alkaline complex, Kola Peninsula: isomorphism and paragenesis

Mitchell

Chakhmouradian

1998

Mineral. mag.

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“…The band at 580 cm −1 was assigned to Nb−μ 2 -O bonds within the sheets. , This represents the majority of Nb−O bonds in the material, giving this absorption the strongest intensity in the spectrum. The broadness of this peak results from inequivalency of the Nb−O bonds that belong to surface and buried Nb-μ 2 -O sites (Figure C).…”

Section: Resultsmentioning

confidence: 99%

Niobate Nanosheets as Catalysts for Photochemical Water Splitting into Hydrogen and Hydrogen Peroxide

2008

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Tetrabutylammonium-stabilized Ca 2 Nb 3 O 10 nanosheets catalyze photochemical splitting of water into hydrogen and hydrogen peroxide under UV irradiation. The peroxide forms on the surface of the catalyst and adsorbs to it, fully deactivating the catalyst after 48 h of irradiation. For the Pt-modified niobate, complete deactivation occurs within 24 h due to higher H 2 evolution rate with this system. The peroxide was identified via Raman and IR spectroscopy. In vibrational spectra, the irradiated niobate exhibits bands at 580, 778, and 940 cm -1 , which suggest that the peroxide is present as a side-on ligand coordinated to the Nb 5+ ions on the nanosheet surface. The same species can be formed by treating the nanosheets with 30% aqueous H 2 O 2 . If the catalyst is irradiated in H 2 18 O, the bands shift to lower energy, indicating that the peroxide species is formed from water. Room-temperature storage of the nanosheets in H 2 18 O also leads to isotopic exchange of all Nb-O atoms over the course of 24 h. Peroxide amounts measured by titration of the catalyst with o-tolidine after 6, 12, and 24 h of irradiation form in a 1:1 stoichiometry with hydrogen. Infrared data shows that the peroxide is partially desorbed by evacuating the catalyst and by purging with argon gas. Under catalytic conditions, this treatment restores up to 60% of the original activity. For the H 2 O 2 -treated catalyst, near quantitative H 2 O 2 desorption occurs within 20 min at 450°C. Separate irradiation experiments of the catalyst in the presence of air reveal that H 2 evolution is diminished and that O 2 uptake occurs from the atmosphere. Most of the hydrogen peroxide formed under these conditions is subsequently detected in the supernatant and only small amounts on the catalyst. NMR spectra show that the tetrabutylammonium cations are decomposed. These findings suggest that there are two distinct pathways for peroxide formation, one involving one-electron reduction of O 2 and one involving two-electron reduction of water (in the absence of O 2 ).

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Phase evolution of strontium bismuth niobate ceramics by conventional solid-state reaction method

Verma

Tanwar

Sreenivas

2018

J Therm Anal Calorim

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Infrared spectra of some niobium minerals

Cited by 3 publications

References 6 publications

Th-rich loparite from the Khibina alkaline complex, Kola Peninsula: isomorphism and paragenesis

Th-rich loparite from the Khibina alkaline complex, Kola Peninsula: isomorphism and paragenesis

Niobate Nanosheets as Catalysts for Photochemical Water Splitting into Hydrogen and Hydrogen Peroxide

Phase evolution of strontium bismuth niobate ceramics by conventional solid-state reaction method

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