Solving modulated structures by X-ray and electron crystallography

Caldés, Maria Teresa; Deniard, Philippe; Zou, Xiaodong; Marchand, R.; Diot, N.; Brec, R.

doi:10.1016/s0968-4328(00)00058-5

Cited by 13 publications

(16 citation statements)

References 25 publications

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“…Similar temperature parameters were reported for Sr(Sr Ta )O (18). Bond valence sum (BVS) calculations (20) using re"ned Sr}O bond distances (Table 2) indicated an abnormally large residual tension about Sr at the A sites (BVS "1.35 v.u., BVS "2 v.u.…”

Section: High-temperature Sr Nb O : Specimens Cooled From T'12503csupporting

confidence: 63%

“…The higher background intensity observed in the neutron di!raction patterns suggests a strong contribution from the oxygen subcell. Recently, a similar modulated background was observed in the neutron powder di!raction patterns of the perovskite-related Sr(Sr Ta )O , with 1:1 cryolite-type ordering of Sr and Ta on the B sites (18).…”

Section: High-temperature Sr Nb O : Specimens Cooled From T'12503csupporting

confidence: 54%

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Complex Polymorphic Behavior and Dielectric Properties of Perovskite-Related Sr(Sr1/3Nb2/3)O3

Levin

Chan

Scott

et al. 2002

Journal of Solid State Chemistry

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Section: High-temperature Sr Nb O : Specimens Cooled From T'12503csupporting

confidence: 63%

Section: High-temperature Sr Nb O : Specimens Cooled From T'12503csupporting

confidence: 54%

Complex Polymorphic Behavior and Dielectric Properties of Perovskite-Related Sr(Sr1/3Nb2/3)O3

Levin

Chan

Scott

et al. 2002

Journal of Solid State Chemistry

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“…This number ratio is in agreement with the composition of NaTaO 3 –Sr(Sr 1/3 Ta 2/3 )O 3 solid solution. Sr(Sr 1/3 Ta 2/3 )O 3 is a known compound, , and its solid solution with NaTaO 3 explains the simultaneous presence of the Sr cations at the A and B sites with no need to create oxygen anion vacancies to balance cationic and anionic charges.…”

Section: Resultsmentioning

confidence: 99%

Local Environment of Strontium Cations Activating NaTaO₃ Photocatalysts

Sasaki

Weidler

et al. 2017

ACS Catal.

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Sodium tantalate, NaTaO 3 , is one of the best semiconductors for photocatalytic water splitting and CO 2 reduction. Doping with metal cations is crucial for enhancing the quantum efficiency of the desired reactions. Nevertheless, details related to the doping of the host metal oxide and activation by guest metal cations are not sufficiently known. The most fundamental question concerns the increase in the quantum efficiency via doping with guest cations that are impurities in the host lattice. In this study, the local environment of Sr cations, which are the typically used guest cations in NaTaO 3 , was characterized by extended X-ray absorption fine structure spectroscopy. The results reveal the presence of two Sr−O shells in the Srdoped NaTaO 3 photocatalysts. The small shell with an unexpectedly short Sr− O bond length of 1.96 Å corresponds to SrO 6 octahedra embedded in the corner-shared network of TaO 6 octahedra. The other shell with a Sr−O bond length of 2.60 Å corresponds to SrO 12 cuboctahedra with Sr cations at positions previously occupied by Na cations. Rietveld analysis of the X-ray diffraction data confirmed the formation of a NaTaO 3 −Sr(Sr 1/3 Ta 2/3 )O 3 solid solution to accommodate the two Sr−O shells in NaTaO 3 with no requirement for creating oxygen anion vacancies. Mechanisms for increasing the quantum efficiency via doping with Sr cations are discussed in the context of the revealed environment.

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“…So, to better visualize the influence of the atoms order on the image contrast a filtered image was calculated. To enhance the contribution of the cation ordering to the image contrast, the (FFT) -1 image was calculating using the supercell model, with the amplitudes of the main reflections weighted down to 30% . The same filtered conditions were applied for the experimental image (Figure ).…”

Section: Resultsmentioning

confidence: 99%

Determination by Means of X-ray Absorption Spectroscopy and Transmission Electron Microscopy of the Local Structure of the 2D-Misfit Compound [Sr(Fe_0.77Nb_0.23)_0.5S_1.5]_1.13NbS₂

Leynaud¹,

Caldés²,

Guillot‐Deudon³

et al. 2003

Chem. Mater.

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The [Sr(Fe0.77Nb0.23)0.5S1.5]1.13NbS2 phase belongs to the 2D-misfit compounds family which are formed of two kinds of slabs labeled Q and H. The Q-part is a three-layer-thick slab, with the NaCl type structure, where external SrS planes enclose the inner (Fe,Nb)S plane. In a previous paper it was shown that there is a statistical distribution of the iron and sulfur atoms in the central layer of the Q-part. On the other hand, niobium atoms adopt an octahedral environment. To get a better description of this central layer, X-ray absorption and HREM studies were undertaken. EXAFS measurements clearly show that the environment of Fe atoms is less complex than that suggested from the structural determination. The existence of only one value for the Fe−S distance confirms the presence of [FeS4] tetrahedra as previously shown by the Mössbauer study. Both [NbS6] and [FeS4] polyhedra can arrange themselves in clusters. Electron diffraction and HREM studies reveal two new additional periodicities which can originate from the arrangement of these clusters. In this paper, a structural model is proposed in the large cell (8a Q × 8b Q × c Q) which takes into account all these new experimental results. This model leads to the [Fe/(Fe+Nb)]Q ratio (0.75) very close to the value deduced from the microprobe analysis.

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Solving modulated structures by X-ray and electron crystallography

Cited by 13 publications

References 25 publications

Complex Polymorphic Behavior and Dielectric Properties of Perovskite-Related Sr(Sr1/3Nb2/3)O3

Complex Polymorphic Behavior and Dielectric Properties of Perovskite-Related Sr(Sr1/3Nb2/3)O3

Local Environment of Strontium Cations Activating NaTaO₃ Photocatalysts

Determination by Means of X-ray Absorption Spectroscopy and Transmission Electron Microscopy of the Local Structure of the 2D-Misfit Compound [Sr(Fe_0.77Nb_0.23)_0.5S_1.5]_1.13NbS₂

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Solving modulated structures by X-ray and electron crystallography

Cited by 13 publications

References 25 publications

Complex Polymorphic Behavior and Dielectric Properties of Perovskite-Related Sr(Sr1/3Nb2/3)O3

Complex Polymorphic Behavior and Dielectric Properties of Perovskite-Related Sr(Sr1/3Nb2/3)O3

Local Environment of Strontium Cations Activating NaTaO3 Photocatalysts

Determination by Means of X-ray Absorption Spectroscopy and Transmission Electron Microscopy of the Local Structure of the 2D-Misfit Compound [Sr(Fe0.77Nb0.23)0.5S1.5]1.13NbS2

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Local Environment of Strontium Cations Activating NaTaO₃ Photocatalysts

Determination by Means of X-ray Absorption Spectroscopy and Transmission Electron Microscopy of the Local Structure of the 2D-Misfit Compound [Sr(Fe_0.77Nb_0.23)_0.5S_1.5]_1.13NbS₂