Phase equilibria and crystal chemistry in the BaO–Al2O3–Nb2O5 and BaO–Nb2O5 systems

Vanderah, Terrell A.; Collins, T.R.; Wong‐Ng, W.; Roth, Robert; Farber, L.

doi:10.1016/s0925-8388(02)00520-0

Cited by 52 publications

(42 citation statements)

References 32 publications

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“…This differs from previous accounts of the structure which present cationic lattices with between 50 -92.5 % of the niobium in tetrahedral coordination 1,[18][19][20][21] . Two types of six-fold oxo-coordinated Nb(V) positions were detected which exhibit NMR parameters that are very distinct from the corresponding four-fold oxo-coordinated species.…”

Section: Discussioncontrasting

confidence: 97%

“…The study by Kemmler-Sack et al 19 describes a palmierite unit cell where 7.5% of the Nb occupy the typically vacant octahedra shown in grey in Figure 2a). A subsequent single crystal XRD study suggested that Ba3Nb2O8 crystallises in the standard palmierite unit cell where only isolated tetrahedra exist 1 . There are a number of potential reasons for these structural discrepancies; firstly there is the comparison between X-ray and neutron data.…”

Section: Discussionmentioning

confidence: 99%

“…The sub-solidus binary system BaO-Nb2O5 contains a number of complex and interesting phases, with several known hexagonal perovskite-derived polytypes lying in the BaO rich region 1 . One example is the compound Ba4Nb2O9 which has been shown to exhibit a number of different polymorphs [2][3][4] .…”

Section: Introductionmentioning

confidence: 99%

“…Hexagonal Ba5Nb4O15 lies close to Ba4Nb2O9, but is a crystallographically simpler system with corner-sharing NbO6 forming perovskite-like blocks, 4 octahedra in thickness, perpendicular to the c-axis of the primitive hexagonal cell 1,7,8 . There are two crystallographically distinct Nb sites, with one showing considerable distortion compared with the other, as determined by both powder and single crystal studies 1,9 .…”

Section: Introductionmentioning

confidence: 99%

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The Crystal Structure of Ba₃Nb₂O₈ Revisited: A Neutron Diffraction and Solid-State NMR Study

et al. 2017

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ABSTRACT:The structure of Ba3Nb2O8 has been investigated using high resolution neutron powder diffraction. Our results show that whilst the structure has some features in common with the 9R perovskite and palmierite structures, it is a new and distinct structure. It is shown to follow a (chh)(hhc)(chh) sequence with BaO3- packing layers and is a cation and aniondeficient 9H perovskite polytype. Nb atoms occupy octahedral sites with vacancies between hexagonal close-packed layers. Isolated, corner-sharing and face-sharing Nb-O octahedra all occur within the unit cell. The identification of purely octahedral Nb is supported by solid state 93 Nb wideline NMR measurements. A two-component line shape was detected: a narrow featureless resonance with an isotropic chemical shift of δiso -928 ± 5 ppm consistent with regular Nb octahedra, and a much broader featureless resonance with an approximate isotropic chemical shift in the range δiso ~-944 --937 ± 10 ppm consistent with Nb octahedra influenced by O vacancies. These are both characteristic of six-fold oxo-coordinated Nb environments. The highly distorted octahedral environments in Ba3Nb2O8 make it a potential candidate for dielectric and photocatalytic applications.

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Section: Discussioncontrasting

confidence: 97%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The Crystal Structure of Ba₃Nb₂O₈ Revisited: A Neutron Diffraction and Solid-State NMR Study

et al. 2017

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“…1f, the crystal structure of Ba 5 Nb 4−x Ta x O 15 belongs to the B-cation deficient hexagonal perovskite-like A n B n−1 O 3n , in which the n − 1 layers of BO 6 octahedra are extended along the (111) planes. 26 The effect of the Ta/Nb ratio on the morphology of Ba 5 Nb 4−x Ta x O 15 crystals was observed by SEM, and the results are shown in Fig. 2.…”

Section: Dalton Transactions Papermentioning

confidence: 99%

The contrasting effect of the Ta/Nb ratio in (111)-layered B-site deficient hexagonal perovskite Ba₅Nb_4−xTa_xO₁₅ crystals on visible-light-induced photocatalytic water oxidation activity of their oxynitride derivatives

et al. 2016

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The effect of the Ta/Nb ratio in the (111) the Ta content up to 50 mol% but decreased at 75 and 100 mol% presumably due to the reduced specific surface area and high density of structural defects, such as grain boundaries acting as recombination centers, originated from high-temperature nitridation for prolonged periods. Transient absorption spectroscopy provided evidence for the effect of the Ta/Nb ratio on the behavior and energy states of photogenerated charge carriers, indicating a direct correlation with photocatalytic water oxidation activity of BaNb 1−x Ta x O 2 N.

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Phase Equilibria and Crystal Chemistry in the BaO—Al₂O₃—Nb₂O₅ and BaO—Nb₂O₅ Systems.

et al. 2003

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system at approximately 1250°C are determined. The new phase Ba 5.75 Al 0.75 Nb 9.25 O 30 with a tetragonal tungsten bronze-type structure (space group P4bm) is found in the system. It exhibits an ambient permittivity of 242 (1 MHz). No indication of ferroelectric behavior is observed in the temperature range 100-400 K. The compound previously reported to occur near 6BaO:7Nb 2 O 5 in the BaO-Nb 2 O 5 system forms as a line compound at 47.5 mol% BaO, with a hexagonal unit cell (space group P6/mmm). Single crystal XRD reveals that Ba 5 Nb 14 O 15 crystallizes in the hexagonal space group P3m1 with Z = 1 and Ba 3 Nb 2 O 8 in the rhombohedral space group R3m with Z = 3. -(VANDERAH*, T. A.; COLLINS, T. R.; WONG-NG, W.; ROTH, R. S.; FARBER, L.;

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Phase equilibria and crystal chemistry in the BaO–Al2O3–Nb2O5 and BaO–Nb2O5 systems

Cited by 52 publications

References 32 publications

The Crystal Structure of Ba₃Nb₂O₈ Revisited: A Neutron Diffraction and Solid-State NMR Study

The Crystal Structure of Ba₃Nb₂O₈ Revisited: A Neutron Diffraction and Solid-State NMR Study

The contrasting effect of the Ta/Nb ratio in (111)-layered B-site deficient hexagonal perovskite Ba₅Nb_4−xTa_xO₁₅ crystals on visible-light-induced photocatalytic water oxidation activity of their oxynitride derivatives

Phase Equilibria and Crystal Chemistry in the BaO—Al₂O₃—Nb₂O₅ and BaO—Nb₂O₅ Systems.

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Phase equilibria and crystal chemistry in the BaO–Al2O3–Nb2O5 and BaO–Nb2O5 systems

Cited by 52 publications

References 32 publications

The Crystal Structure of Ba3Nb2O8 Revisited: A Neutron Diffraction and Solid-State NMR Study

The Crystal Structure of Ba3Nb2O8 Revisited: A Neutron Diffraction and Solid-State NMR Study

The contrasting effect of the Ta/Nb ratio in (111)-layered B-site deficient hexagonal perovskite Ba5Nb4−xTaxO15 crystals on visible-light-induced photocatalytic water oxidation activity of their oxynitride derivatives