Structure of russellite (Bi2WO6): origin of ferroelectricity and the effect of the stereoactive lone electron pair on the structure

The structure of the low-temperature polar (orthorhombic) phase of russellite (Bi2WO6) was examined on artificial specimens with precise single-crystal X-ray diffraction experiments. The final atomic arrangement thus obtained was identical to that reported by Knight [Miner. Mag. (1992), 56, 399–409] with powder neutron diffraction. The residual density attributable to a stereochemically-active lone pair of electrons of bismuth was prominent at approximately the centre of a larger cap of BiO8 square antiprisms, that is on the line from the Bi sites to an adjacent WO4 2− slab along the b-axis direction. Quite uneven Bi—O distances and the formation of a vacant coordination hemisphere (within 3 Å) should, therefore, be ascribed to the strong demand of bismuth to form shorter Bi—O bonds to use up its electrostatic charge within its coordination environment. The shift of bismuth along −c propagates via the correlated shift of the W site and these cooperative shifts cause ferroelectricity in the compound. This propagation was easily effected by the intrusion of molecules such as acetone into the structure.

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Barysilite from Garpenberg Norra, Dalarna, Sweden: occurrence and crystal structure refinement

Mineralogical Magazine ◽

10.1180/0026461026620034 ◽

2002 ◽

Vol 66 (2) ◽

pp. 353-363 ◽

Cited By ~ 1

Author(s):

U. Kolitsch ◽

D. Holtstam

Keyword(s):

Crystal Structure ◽

Lone Electron Pair ◽

Electron Pair ◽

Divalent Cations ◽

Structure Refinement ◽

Direct Proof ◽

Structural Formula ◽

X Ray Diffraction ◽

X Ray ◽

Area Detector

AbstractA new occurrence of barysilite, Pb8Mn(Si2O7)3, at the polymetallic Garpenberg Norra Zn-Pb deposit, Hedemora, Dalarna, Sweden, is described. The mineral, which forms colourless, transparent grains, is characterized by X-ray diffraction and electron-microprobe analyses. The assemblage includes tephroite, zincian jacobsite, manganoan diopside and others. The crystal structure of a barysilite crystal from Garpenberg Norra was redetermined using single-crystal X-ray diffraction data (Mo-Kα, CCD area detector) and has been refined in space group R3̄c with a = 9.804(1), c = 38.416(8)Å, V = 3197.8(8)Å3, to R1 = 2.32% for 1025 ‘observed’ reflections with Fo >4σ(Fo). A previous, low-precision structure determination (Lajzérowicz, 1965; R = 20%) is confirmed but improved considerably. The structure contains one distorted MnO6 polyhedron with six equivalent Mn–O bonds (2.224 Å), one Si2O7 disilicate unit with an Si–O–Si angle of 120.9°, and two non-equivalent Pb sites. The Pb1 site has a highly irregular, one-sided coordination with six O ligands, indicating a stereoactive 6s2 lone-electron pair on the Pb2+ ion, whereas the [6+3]-coordinated Pb2 site is fairly regular, with Pb–O distances of 2.540 (3×), 2.674 (3×) and 3.098 (3×) Å. The Pb2 site contains ~10% of Ca (+Ba) replacing Pb, corresponding to the structural formula Pb16(Pb,Ca)22Mn(Si2O7)3. This is the first direct proof that not only the M site in barysilite-type Pb8M(Si2O7)3 compounds can be replaced by divalent cations.

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The low-temperature and high-pressure crystal structures of cyclobutanol (C4H7OH)

Acta Crystallographica Section B Structural Science ◽

10.1107/s0108768105019191 ◽

2005 ◽

Vol 61 (4) ◽

pp. 449-454 ◽

Cited By ~ 14

Author(s):

Pamela A. McGregor ◽

David R. Allan ◽

Simon Parsons ◽

Colin R. Pulham

Keyword(s):

High Pressure ◽

Low Temperature ◽

Crystal Structures ◽

X Ray Diffraction ◽

Structural Behaviour ◽

Coordination Environment ◽

X Ray ◽

Alkyl Groups ◽

Graph Set ◽

Packing Arrangement

The low-temperature and high-pressure crystal structures of cyclobutanol (C4H7OH) have been determined using single-crystal X-ray diffraction techniques. At temperatures below 220 K, cyclobutanol crystallizes in the Aba2 space group (Z′ = 2) and its crystal structure is composed of pseudo-threefold hydrogen-bonded molecular catemers [assigned as C_2^2(4) in graph-set notation], which lie parallel to the crystallographic a axis. At a pressure of 1.3 GPa, the crystal symmetry changes to Pna21 (Z′ = 1) and the molecular catemers [expressed as C(2) in graph-set notation] adopt a pseudo-twofold arrangement. This structural behaviour is in agreement with our previous observations for phenol and its halogenated derivatives 2-chlorophenol and 4-fluorophenol, where pressure was found to favour a molecular packing more closely associated with small alkyl groups rather than that of relatively bulky alkyl groups. In addition, an examination of the molecular coordination environment in the low-temperature and high-pressure structures of cyclobutanol reveals that the change in structure on application of pressure appears to be driven by the molecules assuming a packing arrangement which more closely resembles that adopted in hard-sphere structures.

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Crystal Structure of the Disordered Non-Centrosymmetric Compound Fe0.43Mo2.56SbO9.5

Crystals ◽

10.3390/cryst9010040 ◽

2019 ◽

Vol 9 (1) ◽

pp. 40

Author(s):

Sk Ali ◽

Sven Lidin ◽

Mats Johnsson

Keyword(s):

Crystal Structure ◽

Diffraction Data ◽

Lone Electron Pair ◽

Electron Pair ◽

Building Blocks ◽

Fold Axis ◽

X Ray Diffraction ◽

Unit Cell Parameters ◽

X Ray ◽

Cell Parameters

Single crystals of Fe0.43Mo2.56SbO9.5 were obtained by hydrothermal techniques at 230 °C. The crystal structure was determined from single crystal X-ray diffraction data. The compound crystallizes in the non-centrosymmetric space group Pc with unit cell parameters a = 4.0003(2) Å, b = 7.3355(3) Å, c = 12.6985(6) Å, β = 90°. The crystal structure comprises five crystallographically independent M atoms and one Sb3+ atom, M atoms are of two kinds of partially occupied sites Mo6+ and Fe3+. The building blocks consist of [SbO3O0.5O0.5E] octahedra (E = lone electron pair) and [(Mo/Fe)O6] octahedra. The M = (Mo, Fe) and O atoms are arranged in a distorted hexagonal 2D-net, not the Sb atoms. The distortion of the net and consequently the symmetry reduction results mainly from the location of the Sb atoms. Disorder manifests itself as a splitting of the metal sites and as a consequent shortening of the Mo–Fe distances. Six (Mo/Fe)O6 octahedra are connected to form a pseudohexagonal channel. The Sb3+ atom is displaced from the pseudo-six-fold axis.

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Pressure Dependence of the Tetragonal-Orthorhombic Transition in La1.88 Sr0.12 Cu O4-δ: A Single Crystal X-Ray Study

MRS Proceedings ◽

10.1557/proc-99-497 ◽

1987 ◽

Vol 99 ◽

Author(s):

R. Moret ◽

G. Collin

Keyword(s):

High Pressure ◽

Transition Temperature ◽

Low Temperature ◽

Single Crystal ◽

Diffraction Study ◽

Pressure Dependence ◽

Orthorhombic Phase ◽

X Ray Diffraction ◽

X Ray

ABSTRACTWe report the first combined high pressure (up to 30 kbar) and low temperature (10 K - 300 K) single crystal X-ray diffraction study of the tetra-gonal-orthorhombic transition in La2−xCuO4-δ(x=0.12). Superstructure reflections of the orthorhombic phase were used to characterize the transition. The transition temperature, TT–O, is found to decrease under pressure and the orthorhombic phase is suppressed above about 15 kbar. These results confirm that both phases are superconducting and suggest to attribute a previously reported kink in dTc/dP to different rates of increase of Tc for the tetragonal and orthorhombic phases.

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Notizen: Über zwei Bleiantimonphosphate mit Eulytinstruktur: Pb3SbIII(PO4)3 und Pb11SbV(PO4)9/On two Lead Antimony Phosphates with Eulytine Structure: Pb3SbIII(PO4)3 and Pb11SbV(PO4)9

Zeitschrift für Naturforschung B ◽

10.1515/znb-1980-0628 ◽

1980 ◽

Vol 35 (6) ◽

pp. 771-772 ◽

Cited By ~ 2

Author(s):

Günter Engel ◽

Jutta Belgardt

Keyword(s):

Cell Volume ◽

Lattice Constant ◽

Thermal Behaviour ◽

Lone Electron Pair ◽

Electron Pair ◽

Large Cell ◽

X Ray Diffraction ◽

X Ray ◽

Stereochemical Activity ◽

Characteristic Manner

Abstract Two lead antimony phosphates have been prepared, which both crystallize with the cubic eulytine structure. Pb3SbIII(PO4)3 has the lattice constant a= 1037.2 pm and Pb11SbV(PO4)9 has a = 1037.5 pm. The X-ray diffraction diagrams appear nearly identical. In their chemical and thermal behaviour these compounds differ in a characteristic manner, however. The relatively large cell volume of Pb3Sb(PO4)3 is attributed to the very distinct stereochemical activity of the lone electron pair of Sb3+.

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The preparation of bis(perfluoroethyl) tellurium difluoride and dichloride, trans perfluoroethyl tellurium monochloride tetrafluoride, trans bis(perfluoroethyl) tellurium tetrafluoride; and the preparation and X-ray crystal structure of perfluoroethyl tellurium trifluoride

Canadian Journal of Chemistry ◽

10.1139/v85-374 ◽

1985 ◽

Vol 63 (8) ◽

pp. 2273-2280 ◽

Cited By ~ 18

Author(s):

Clement Lau ◽

Jack Passmore ◽

E. Keith Richardson ◽

Tom K. Whidden ◽

Peter S. White

Keyword(s):

Vibrational Spectra ◽

Electron Pair ◽

Lone Pair ◽

Axial Position ◽

X Ray Diffraction ◽

Tellurium Atom ◽

Nmr Spectrum ◽

X Ray ◽

R Factor ◽

Trigonal Bipyramidal

The reaction of (C2F5)2Te and XeF2 in a slurry of SO2ClF yielded (C2F5)2TeF2 essentially quantitatively. Chlorine and (C2F5)2Te gave (C2F5)2TeCl2. Both (C2F5)2TeF2 and (C2F5)2TeCl2 were assigned a trigonal bipyramidal geometry, on the basis of their 19F nmr and vibrational spectra, with the lone pair and C2F5 groups in equatorial, and the halogens in the axial positions. Perfluoroethyl tellurium trifluoride was prepared essentially quantitatively by the reaction of C2F5TeTeC2F5 and XeF2 in liquid SO2F2. The generally inert SO2ClF was found to react with C2F5TeTeC2F5 to give C2F5TeClxF3−x, and sulphur dioxide. The structure of C2F5TeF3 was determined by X-ray diffraction. The crystals are tetragonal with a = 10.129(4), c = 25.561(6) Å, and Z = 16. The structure was refined in space group I41/a to a conventional R factor of 0.051 for 901 observed reflections with I ≥ 3σ(I). Each tellurium atom is surrounded by two terminal fluorine atoms and two bridging fluorine atoms and a C2F5 group in an axial position around the apex of a distorted square pyramid. The square-pyramidal units are linked by symmetrical cis bridging atoms into endless chains with bridging angles of 180° and 177°. The geometry of the (C2F5TeF4) group is consistent with steric activity of the non-bonded electron pair. The 19F nmr and Raman spectra of C2F5TeF3 were recorded and the Raman spectrum assigned. Trans-C2F5TeClF4 was prepared by the reaction of C2F5TeTeC2F5, and an excess of ClF. The trans octahedral geometry of C2F5TeClF4 was unambiguously assigned from its 19F nmr and vibrational spectra. A mixture of trans-(C2F5)2TeF4 and trans-C2F5TeClF4 was obtained from the reaction of (C2F5)2Te and an excess of ClF. Trans geometry of (C2F5)2TeF4 was unambiguously assigned from its 19F nmr spectrum.

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Revisiting La0.5Sr1.5MnO4lattice distortion and charge ordering with multi-beam resonant diffraction

Acta Crystallographica Section A Foundations and Advances ◽

10.1107/s2053273316013759 ◽

2017 ◽

Vol 73 (1) ◽

pp. 46-53

Author(s):

Wen-Chung Liu ◽

Yi-Hua Chiu ◽

Ying-Yu Kung ◽

Po-Yu Liao ◽

Chih-Hao Cheng ◽

...

Keyword(s):

Low Temperature ◽

Momentum Transfer ◽

Orthorhombic Phase ◽

Diffraction Theory ◽

Charge Ordering ◽

Sinusoidal Wave ◽

X Ray Diffraction ◽

Wave Type ◽

X Ray ◽

Small Charge

Sinusoidal wave type distortions of La0.5Sr1.5MnO4in the low-temperature orthorhombic phase were observed using multi-beam resonant X-ray diffraction (MRXD) with (7/4 7/4 0) fractional primary diffraction. Two four-beam diffractions with opposite asymmetry were measured at 6.5545 keV and compared with the curves simulated by the dynamical X-ray diffraction theory. This approach provides the possibility of resolving the distortion modes which are perpendicular to the momentum transfer by a single azimuthal scan. The paper also demonstrates the sensitivity of MRXD profilesversusincident X-ray energy in the vicinity of the MnKedge to the charge disproportion between the two manganese sites, reconfirming the small charge disproportion feature.

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Microdomains in BaFeO3-y (0.35 < y < 0.50)

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100177039 ◽

1990 ◽

Vol 48 (4) ◽

pp. 780-781

Author(s):

M. Vallet-Regí ◽

M. Parras ◽

J.M. González-Calbet ◽

J.C. Grenier

Keyword(s):

Electron Diffraction ◽

Chemical Analysis ◽

Monoclinic Phase ◽

Orthorhombic Phase ◽

Total Iron ◽

Zone Axis ◽

Electron Micrograph ◽

X Ray Diffraction ◽

X Ray ◽

Compositional Variations

BaFeO3-y compositions (0.35<y<0.50) have been investigated by means of electron diffraction and microscopy to resolve contradictory results from powder X-ray diffraction data.The samples were obtained by annealing BaFeO2.56 for 48 h. in the temperature range from 980°C to 1050°C . Total iron and barium in the samples were determined using chemical analysis and gravimetric methods, respectively.In the BaFeO3-y system, according to the electron diffraction and microscopy results, the nonstoichiometry is accommodated in different ways as a function of the composition (y):In the domain between BaFeO2.5+δBaFeO2.54, compositional variations are accommodated through the formation of microdomains. Fig. la shows the ED pattern of the BaFeO2.52 material along thezone axis. The corresponding electron micrograph is seen in Fig. 1b. Several domains corresponding to the monoclinic BaFeO2.50 phase, intergrow with domains of the orthorhombic phase. According to that, the ED pattern of Fig. 1a, can be interpreted as formed by the superposition of three types of diffraction maxima : Very strong spots corresponding to a cubic perovskite, a set of maxima due to the superposition of three domains of the monoclinic phase along [100]m and a series of maxima corresponding to three domains corresponding to the orthorhombic phase along the [100]o.

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