The incommensurate modulation of the structure of Sr2Nb2O7

Daniels, Peter J. L.; Tamazyan, R. А.; Kuntscher, C. A.; Dressel, Martin; Lichtenberg, F.; Smaalen, Sander van

doi:10.1107/s010876810201741x

Cited by 35 publications

(35 citation statements)

References 11 publications

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“…An important application is the analysis of the rotations of the BO 6 octahedral groups in perovskites ABO 3 and compounds derived from the perovskite structure type. Common characteristic of these compounds is a framework of corner-sharing BO 6 octahedra with the A cations filling the space in between. Many different compounds of this type are known, with a great variety of superstructures and incommensurately modulated structures.…”

Section: Structural Chemistry Of Incommensurate Crystalsmentioning

confidence: 99%

“…Eq. (6) shows that a translation of a s;i in superspace comprises a translation of a i in 3D space combined with a translation Às i along the fourth coordinate in superspace. The latter is exactly the required phase shift of the arguments of the modulation functions.…”

Section: Superspace Symmetrymentioning

confidence: 99%

“…An example is the compound Sr 2 Nb 2 O 7 , that possesses an incommensurately modulated structure with q ¼ ð0:488; 0; 0Þ [6]. The basic structure consists of slabs with a distorted perovskite type structure of 4 octahedra wide, that are alternately stacked along the b axis with layers of extra oxygen atoms (Fig.…”

Section: Structural Chemistry Of Incommensurate Crystalsmentioning

confidence: 99%

“…The formal theory of the symmetry of aperiodic crystals was introduced by Janner and Janssen [3][4][5]. 3a, 4a, 8c and 8d of [6]). …”

Section: Introductionmentioning

confidence: 99%

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An elementary introduction to superspace crystallography

Smaalen¹

2004

Zeitschrift Für Kristallographie - Crystalline Materials

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Abstract. Aperiodic crystals are defined as a crystalline state of matter, that has atomic structures with long-range order but without translational symmetry. Experimentally, they are characterized by sharp Bragg reflections in the Xray diffraction, that can be indexed by integers, if four or more reciprocal basis vectors are used. An introduction is given to the basic concepts of the superspace theory for structural analysis of incommensurately modulated crystals and incommensurate composite crystals [De Wolff, Janner and Janssen, Acta Crystallogr. 37 (1981) 625-636]. It is concluded that major challenges of the crystallography of incommensurate phases lie in the determination of the precise shapes of modulation functions, and in finding the relations between physical properties of incommensurate crystals and their atomic structures.

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Section: Structural Chemistry Of Incommensurate Crystalsmentioning

confidence: 99%

Section: Superspace Symmetrymentioning

confidence: 99%

Section: Structural Chemistry Of Incommensurate Crystalsmentioning

confidence: 99%

“…The formal theory of the symmetry of aperiodic crystals was introduced by Janner and Janssen [3][4][5]. 3a, 4a, 8c and 8d of [6]). …”

Section: Introductionmentioning

confidence: 99%

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An elementary introduction to superspace crystallography

Smaalen¹

2004

Zeitschrift Für Kristallographie - Crystalline Materials

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“…The obtained peak patterns well correspond with previous investigations, and show no impurity phases. [7,8] A typical size of measured sample was 4×4×0.5 mm 3 . To measure the anisotropic properties, the directions of the axes were determined by the four-axes x-ray diffraction analysis.…”

Section: Sample Preparations and Methodsmentioning

confidence: 99%

Large anisotropic thermoelectricity in perovskite related layered structure: Sr_nNb_nO_3n+2(n= 4,5)

Sakai

Takahashi

Kanno

et al. 2011

IOP Conf. Ser.: Mater. Sci. Eng.

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Abstract.We have systematically synthesized a series of perovskite related layered structures, Strontium-Niobates expressed as SrnNbnO3n+2 (n = 4 ∼ 5) and focused on the thermoelectricity in n = 4 and 5 type materials here. To explore their thermoelectricities and anisotropic properties, we have measured the thermal and charge transport properties along all crystallographic axes. The values of thermoelectric parameters were strongly anisotropic and there exists a large anisotropy even in in-plane direction of the layered structure. As a result, the best performance of thermoelectricity is commonly observed in the a-axis. The respective ZT for Sr1.8La0.2Nb2O7 and Sr5Nb5O17 at room temperature is 3.5×10 −2 and 3.6×10 −3 . IntroductionConsidering recent problems on global environment, application devices are required that efficiently convert waste of heat into electric power. A thermoelectric phenomenon, which uses a solid-state conversion, is supposed to be the solution technology. To efficiently generate the electric power, it is necessary to develop materials with a higher ZT value. Here, ZT is dimensionless figure of merit, which is expressed as the ZT =S 2 T ρ −1 κ −1 (S:Seebeck coefficient, ρ:resistivity, κ:thermal conductivity). Oxide materials with highly electric conduction often show the good thermoelectricity at high temperature. So far, several oxides have attracted much attention for their high thermoelectric performance and stability in air, for examples, CdI 2 -type layered cobaltites [1,3] or Ruddlesden-Ropper type perovskite titanates [2] etc. In such materials, most have anisotropic crystal structures (layers or columns, etc) and their anisotropy in structures plays an important role for the high thermoelectricity. Therefore, introducing anisotropy into the structure is one of the strategies to improve the ZT value. In this scheme, a number of works have been reported, especially for two-dimensional layered materials including the cobaltites etc. However, for one-dimensional materials, few works have been reported, [4,5] and the development of material has not been fully done yet. Strontium-niobate system Sr n Nb n O 3n+2 is known as one of the pseudo-one-dimensional electric conductors.[6] Their crystal structures belong to a perovskite related layered structure. The constituent layers stack along the c-axis, and NbO 6 octahedra in the layers are aligned straightly along the a-axis and in a staggered manner along the b-axis with corner-sharing. The schematic illustrations of the typical structures for n = 4 and 5 are shown in the

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Incommensurate–Commensurate Transition in the Geometric Ferroelectric LaTaO₄

Howieson

Gibbs

et al. 2020

Adv Funct Materials

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The layered perovskite LaTaO 4 has been synthesized to be stable in both (polar) orthorhombic and (nonpolar) monoclinic polymorphs at ambient conditions. Although the structural transition between monoclinic and orthorhombic phases has been well established, there is some controversy regarding a further, unidentified transition around 500 K. Here this is identified as an incommensurate-commensurate first-order transition between incommensurate Cmc2 1 (α00)0s0 and commensurate Cmc2 1 orthorhombic phases. Transmission electron microscopy indicates partially ordered stacking of different structural units in a, identifying the local cause for the modulation, whereas variable temperature powder neutron diffraction has shown the overall macroscopic modulation vector, q ≈ (0.456, 0, 0)-roughly a 2.2 × expansion in a, corresponding to an approximate 11a commensurate superunit cell dimension. The modulation shows a continuous temperature dependence until transitioning to the basic (commensurate) cell at T IC-C. Doping the interlayer La sites with smaller Nd cations stabilizes the incommensuration to higher temperature, suggesting the modulation is geometrically driven at the A site.

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The incommensurate modulation of the structure of Sr₂Nb₂O₇

Cited by 35 publications

References 11 publications

An elementary introduction to superspace crystallography

An elementary introduction to superspace crystallography

Large anisotropic thermoelectricity in perovskite related layered structure: Sr_nNb_nO_3n+2(n= 4,5)

Incommensurate–Commensurate Transition in the Geometric Ferroelectric LaTaO₄

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The incommensurate modulation of the structure of Sr2Nb2O7

Cited by 35 publications

References 11 publications

An elementary introduction to superspace crystallography

An elementary introduction to superspace crystallography

Large anisotropic thermoelectricity in perovskite related layered structure: SrnNbnO3n+2(n= 4,5)

Incommensurate–Commensurate Transition in the Geometric Ferroelectric LaTaO4

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The incommensurate modulation of the structure of Sr₂Nb₂O₇

Large anisotropic thermoelectricity in perovskite related layered structure: Sr_nNb_nO_3n+2(n= 4,5)

Incommensurate–Commensurate Transition in the Geometric Ferroelectric LaTaO₄