Articoli di riviste: "Quenched-in fluorite type structure"

1

Webster, Nathan A. S., Chris D. Ling e Frank J. Lincoln. "Structure–property relationships in fluorite-type Bi2O3–Yb2O3–PbO solid-electrolyte materials". Powder Diffraction 29, S1 (21 novembre 2014): S73—S77. http://dx.doi.org/10.1017/s0885715614001079.

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New quenched-in face-centred cubic fluorite-type materials were synthesised in the Bi2O3–Yb2O3–PbO system. After annealing in air at 500 °C for up to 200 h, each material underwent a conductivity-lowering structural transformation, thus making them unsuitable for use as solid electrolytes in solid-oxide fuel cells. For example, (BiO1.5)0.80(YbO1.5)0.17(PbO)0.03 underwent a fluorite- to Bi17Yb7O36-type orthorhombic transformation, indicative of long-range cation ordering, and (BiO1.5)0.80(YbO1.5)0.11(PbO)0.09 underwent a fluorite- to β-Bi2O3-type tetragonal transformation, indicative of long-range 〈001〉 oxide-ion vacancy ordering.

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Landa-Cánovas, Á. R., Eladio Vila, Jorge Hernández-Velasco, Jean Galy e Alicia Castro. "Transmission Electron Microscopy Study of Low Mo-content Bi-Mo-O Phases". Microscopy and Microanalysis 18, S5 (agosto 2012): 71–72. http://dx.doi.org/10.1017/s1431927612013013.

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δ-Bi2O3, a material with a fluorite-type structure, is one of the best solid-state oxygen-ion conductors. It is a high-temperature form that cannot be quenched to room temperature. However, doping with small amounts of transition metal oxides preserves the δ-Bi2O3 structure at low temperature and retains its anionic conduction properties. The Bi2O3–MoO3 materials are interesting because of their functional properties, chiefly as catalysts and as good ionic conductors. All the phases in this system are related to the fluorite structure except Bi2MoO6 which shows an Aurivillius-type structure.

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Sorokin, N. I. "Polarizability of Fluoride Ions in Fluorides with Fluorite-Type Structure". Crystallography Reports 45, n. 6 (novembre 2000): 976. http://dx.doi.org/10.1134/1.1327662.

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Lucid, Aoife K., Aoife C. Plunkett e Graeme W. Watson. "Predicting the Structure of Grain Boundaries in Fluorite-Structured Materials". Johnson Matthey Technology Review 63, n. 4 (1 ottobre 2019): 247–54. http://dx.doi.org/10.1595/205651319x15598975874659.

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Interfaces are a type of extended defect which govern the properties of materials. As the nanostructuring of materials becomes more prevalent the impact of interfaces such as grain boundaries (GBs) becomes more important. Computational modelling of GBs is vital to the improvement of our understanding of these defects as it allows us to isolate specific structures and understand resulting properties. The first step to accurately modelling GBs is to generate accurate descriptions of the structures. In this paper, we present low angle mirror tilt GB structures for fluorite structured materials (calcium fluoride and ceria). We compare specific GB structures which are generated computationally to experimentally known structures, wherein we see excellent agreement. The high accuracy of the method which we present for predicting these structures can be used in the future to predict interfaces which have not already been experimentally identified and can also be applied to heterointerfaces.

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Withers, RL, JG Thompson, PJ Barlow e JC Barry. "The Defect Fluorite Phase in the ZrO2-PrO1.5 System and Its Relationship to the Structure of Pyrochlore". Australian Journal of Chemistry 45, n. 9 (1992): 1375. http://dx.doi.org/10.1071/ch9921375.

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A detailed transmission electron microscope and X-ray powder diffraction study has been made of the so-called 'defect fluorite' phase field in the ZrO2-PrO1.5 system and of its close relationship to the pyrochlore solid solution field in the same system. Even for the lowest possible PrO1.5 content within the 'defect fluorite' phase field, it is clear that the sharp Bragg reflections characteristic of the underlying fluorite average structure are accompanied by some of the 'satellite reflections' characteristic of the pyrochlore solid solution field. As the PrO1.5 content increases, these satellite reflections increase systematically in intensity as well as sharpening very considerably. It is shown that this 'defect fluorite' phase field cannot be adequately described either in terms of random point defects within an average fluorite-type matrix or in terms of a diphasic texture of pyrochlore domains embedded coherently into a fluorite matrix, but must be regarded as enuinely intermediate between these two end-member structures and of commensurately modulated fluorite type. A group theoretical approach is used to propose a model for the structural deviation from the underlying fluorite average structure.

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Shiraki, Koichi, Taku Tsuchiya e Shigeaki Ono. "Structural refinements of high-pressure phases in germanium dioxide". Acta Crystallographica Section B Structural Science 59, n. 6 (25 novembre 2003): 701–8. http://dx.doi.org/10.1107/s0108768103021761.

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Recently, there has been substantial interest in the new high-pressure polymorphs of GeO2 synthesized in the laboratory. Previous investigators reported the synthesis of `CaCl2-type', `α-PbO2-type' and `pyrite-type (modified-fluorite-type)' GeO2 at pressures of 30–130 GPa in laser-heated diamond anvil cells. In order to provide definitive information about the new high-pressure polymorphs, we performed Rietveld refinements of the structures. The structure refinements confirm that two of these high-pressure phases do have the α-PbO2-type and pyrite-type (modified-fluorite-type) structures.

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Ye, Fei, Ding Rong Ou e Toshiyuki Mori. "Microstructural Evolution in a CeO2-Gd2O3 System". Microscopy and Microanalysis 18, n. 1 (15 dicembre 2011): 162–70. http://dx.doi.org/10.1017/s1431927611012396.

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AbstractMicrostructural evolution in a CeO2-Gd2O3 system at atomic and nanoscale levels with increasing Gd concentration has been comprehensively investigated by transmission electron microscopy. When the Gd concentration was increased from 10 to 80 at.%, the phase transformation from ceria with fluorite structure to solid solution with C-type structure was not a sudden change but an evolution in the sequence of clusters, domains, and precipitates with C-type structure in the fluorite-structured matrix. Moreover, the ordering of aggregated Gd cations and oxygen vacancies in these microstructural inhomogeneities developed continuously with increasing Gd concentration. This microstructural evolution can be further described based on the development of defect clusters containing Gd cations and oxygen vacancies.

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Rossell, HJ, M. Leblanc, G. Ferey, DJM Bevan, DJ Simpson e MR Taylor. "On the Crystal Structure of Bi2Te4O11". Australian Journal of Chemistry 45, n. 9 (1992): 1415. http://dx.doi.org/10.1071/ch9921415.

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Bi2Te4O11 is monoclinic, space group P21/n; the lattice parameters derived from a Guinier powder pattern ( Si standard) are: a = 6.9909(3), b = 7.9593(3), c = 18.8963(8) � , β = 95.176(3)�, Z = 4, V = 1047.15 �. The structure was solved independently from both single-crystal X-ray data and a combination of X-ray and neutron powder data. It is an anion-deficient superstructure of fluorite in which can be recognized the ordered intergrowth of fluorite-type Bi2Te2O7 and rutile-type Te2O4. Lone-pair electrons are stereochemically active.

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9

Achary, S. N., S. J. Patwe e A. K. Tyagi. "Powder XRD study of Ba4Eu3F17: A new anion rich fluorite related mixed fluoride". Powder Diffraction 17, n. 3 (settembre 2002): 225–29. http://dx.doi.org/10.1154/1.1477198.

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The compound Ba4Eu3F17 was prepared by heating pre-dried BaF2 and EuF3 (4:3) at 800 °C for 8 h in static vacuum. The colorless polycrystalline product obtained was characterized by Rietveld refinement of the observed powder diffraction data with a starting model of Ba4Y3F17. The title compound Ba4Eu3F17 crystallizes in rhombohedral lattice with lattice parameters, a=11.1787(4) and c=20.5789(10) Å, Z=3 (Space group R 3, No. 148). The Ba4Eu3F17 structure can be described as an ordered anion-rich fluorite type structure with the formation of Eu6F37 clusters. There are two crystallographically distinct Ba (CN=10, 11) and one distinct Eu (CN=8). The typical Ba(1)–F, Ba(2)–F, and Eu–F bond lengths range from 2.56 to 2.83 Å, 2.54 to 3.25 Å, and 2.24 to 2.49 Å, respectively. The salient feature of the structure is that the EuF8 polyhedra share their corner to form a cubo-octahedron of fluoride ions. The cubic BaF8 polyhedra of BaF2 are modified to Ba(1)–F10 and Ba(2)–F11 polyhedra in this structure. The cubo-octahedron encloses extra fluorine F(8) inside it.

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Kennedy, Brendan, Peter Blanchard, Emily Reynolds e Zhaoming Zhang. "Transformation from pyrochlore to fluorite by diffraction and X-ray spectroscopy". Acta Crystallographica Section A Foundations and Advances 70, a1 (5 agosto 2014): C234. http://dx.doi.org/10.1107/s2053273314097654.

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We have studied the long-range average and local structures in a number of zirconium containing materials of the type A2B2O7 ( A = Ln or Y; B = Zr, Hf or Sn) using synchrotron X-ray and neutron powder diffraction and X-ray absorption spectroscopy. Studies of the system Gd2-xTbxZr2O7 include neutron diffraction data, obtained at λ ≍ 0.497 Å to minimise absorption, not only provide evidence for independent ordering of the anion and cation sublattices, but also suggest that the disorder transition across the pyrochlore-defect fluorite boundary of Ln2Zr2O7 is rather gradual. In general we observe that while the diffraction data indicate a clear phase transition from ordered pyrochlore to disordered defect-fluorite at specific compositions corresponding to a critical ionic radius ratio of the A and B cations (rA/rB) x ~ 1.0-1.2, X-ray absorption near-edge structure (XANES) results reveal a gradual structural evolution across the compositional range. These findings provide experimental evidence that the local disorder occurs long before the pyrochlore to defect-fluorite phase boundary as determined by X-ray diffraction, and the extent of disorder continues to develop throughout the defect-fluorite region. Where possible the experimental results were supplemented by ab initio atomic scale simulations, which provide a mechanism for disorder to initiate in the pyrochlore structure. Further, the coordination numbers of the cations in both the defect-fluorite and pyrochlore structures were predicted, and the trends agree well with the experimental XANES results. X-ray absorption measurements at the Zr L3-edge, which showed a gradual increase in the effective coordination number of the Zr from near 6-coordinate in the pyrochlore rich samples to near 7-coordinate in the defect fluorites.

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Schneider, Julius, e Wolfgang Schmahl. "Superionic phase transitions in anti-fluorite structures". Acta Crystallographica Section A Foundations and Advances 70, a1 (5 agosto 2014): C72. http://dx.doi.org/10.1107/s2053273314099276.

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Fast ion conductors attract continuous and increasing interest in view of possible applications in battery technology. Early examples of superionic phase transitions in anti-fluorite type structures, where the small cations reside in a tetrahedral cage of large anions include Ag2Te [1]. At elevated temperatures anharmonic atom thermal displacements induce cation diffusion towards the large void formed by the central anion octahedron. Of the anti-fluorite structure type compounds Li2 X, where X=(O, S, Se, Te), the compounds Li2O and Li2S showed diffuse transitions to a superionic phase. Very recent advances in battery technology of these compounds [2] motivated us to investigate the end member Li2Te [3] by temperature dependent neutron powder diffraction. The quasi-harmonic temperature dependence of the Li thermal displacement factor shows a distinct steepening of slope around 4000C, indicating a phase transition to a superionic phase. Analysis of derived probability density functions and atom potentials again reveal a corresponding increase of anharmonic, anisotropic Li-ion motion towards the octahedral void. This indicates opening up of Li-ion diffusion pathways at the phase transition. The superionic phase transitions of the Li2X anti-fluorite type structures are steered by their cation-anion distance ratio, which in turn determines their respective transition temperatures. The superionic phase transitions mark the onset of cation sublattice melting, where these transition temperatures are proportional to the melting temperatures of the entire compounds.

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Pérez-Estébanez, M., R. Pastrana-Fábregas, J. Isasi-Marín e R. Sáez-Puche. "Inorganic pigments based on fluorite-type oxynitrides". Journal of Materials Research 21, n. 6 (1 giugno 2006): 1427–33. http://dx.doi.org/10.1557/jmr.2006.0177.

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Zirconia oxynitride rare-earth-doped pigments were prepared by ammonolysis of the zirconium rare-earth oxides, previously synthesized using the citrate complexation/calcination route. Different coloration has been obtained, the intensity of which is a function of the nitrogen amount in the case of the oxynitrides; in the case of the oxides, both color and intensity depend on the doping amount of rare earth. The obtained phases, Zr(1−x)CexO2, Zr(1−x)RxO(2−x/2)□x/2, with R = Eu or Er and Zr(1−x)RxO(2−x/2−3/2y)Ny□x/2■y/2 (R = Ce, Eu, and Er), have been characterized by x-ray powder diffraction, scanning electron microscopy, and reflectance spectra data. These results show that the phases with minor rare-earth concentration adopt a baddeleyite-type structure, with a monoclinic symmetry, space group P21/c. By increasing the rare-earth doping, the obtained phases crystallize with the fluorite structure with tetragonal (P42/nmc) or cubic symmetry (Fm¯3m). On the other hand, the study of the magnetic properties of the oxides and oxynitrides indicate a paramagnetic behavior, and in the case of the cerium oxide, the nitridation process produces the reduction from Ce4+ to Ce3+. Diffuse reflectance data and CIE-LAB color coordinates suggest that these ceramics based on nitrogen containing zirconia are expected to be promising candidates as new ecological inorganic pigments.

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Checchia, Stefano, Marco Scavini, Mattia Allieta, Michela Brunelli, Claudio Ferrero e Mauro Coduri. "Size and spatial correlation of defective domains in yttrium-doped CeO2". Powder Diffraction 30, S1 (22 maggio 2015): S119—S126. http://dx.doi.org/10.1017/s0885715615000135.

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The size of dopant-rich nanodomains was assessed in four samples of Ce1−μYμO2−μ/2 through systematic pair distribution function (PDF) refinements. Experimental G(r) curves were fitted by different structural models with the aim of finding a description which balanced precise structure parameterization and reasonable number of parameters. The most reliable model was a single Y2O3-like phase, which best accommodated to the close relationship between the fluorite (CeO2-like) and C-type (Y2O3-like) structures. In this model, a refined cation coordinate, x(M2), measured the relative occurrence in the G(r) of the chemical environment of Y and Ce at any value of r. The r-value at which x(M2) vanished, i.e. at which the refined C-type cell becomes a redundant, low-symmetry description of a fluorite cell, was assumed as the size of a C-type domain. Subtle features in G(r) could be attributed to the fluorite or C-type phase up to ~500 Å thanks to the narrow instrumental resolution function of the ID31 beamline (now ID22) at the ESRF, which allows us to get high resolution PDF data.

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Ling, Christopher D., Siegbert Schmid, Ray L. Withers, John G. Thompson, Nobuo Ishizawa e Shunji Kishimoto. "Solution and refinement of the crystal structure of Bi7Ta3O18". Acta Crystallographica Section B Structural Science 55, n. 2 (1 aprile 1999): 157–64. http://dx.doi.org/10.1107/s0108768198011148.

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The structure of heptabismuth tritantalum octadecaoxide, Bi7Ta3O18, has been solved and refined using single-crystal X-ray diffraction data collected at a synchrotron source in conjunction with unit-cell and symmetry information derived from electron diffraction. The space-group symmetry is triclinic C1 but is very close to monoclinic C2/m. A twin component observed during data collection was successfully modelled in the refinement. The C2/m prototype fitted all the Rietveld-refinable features of a medium-resolution neutron powder diffraction pattern. The metal-atom array is approximately face-centred cubic (fluorite type), punctuated by regularly spaced displacement faults perpendicular to the [111]fluorite direction every 2.5 fluorite unit cells. The metal-atom populations and O-atom positions are fully ordered. The Ta5+ cations are octahedrally coordinated, with TaO6 octahedra forming columns. The remaining O atoms occupy distorted fluorite positions. The Bi3+ cations occupy octahedral, square pyramidal or trigonal prismatic sites within the O-atom array; strain in the latter coordination environment appears to be responsible for the lowering of symmetry from monoclinic to triclinic.

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Muñoz, R. A., Paola Cristina Cajas, J. E. Rodriguez, A. C. Rodrigues e Cosme R. M. Silva. "Polycrystalline Tetragonal Zirconia of the Form ZrO₂: 3 mol% Re₂O₃ (Re-TZP) for Use in Oxygen Sensors: Synthesis, Characterization and Ionic Conductivity". Materials Science Forum 798-799 (giugno 2014): 145–53. http://dx.doi.org/10.4028/www.scientific.net/msf.798-799.145.

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Oxygen ion conductors of zirconia based ceramics are a class of materials with technological applications in several application areas: sensors of chemical species, oxygen pumps, solid oxide fuel cells among others [1]. For these applications, the zirconia must possess the fluorite type crystal structure, or close to it. Such oxides with this structure are the classic oxygen ion conductors [2]. The fluorite structure consists of a cubic lattice of oxygen ions surrounded by cations. The cations are arranged in a face centered cubic structure with anions occupying tetrahedral positions. This leads to an open structure with large empty octahedral interstices.

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Ho, Herbert L., Charles L. Bauer, Subhash Mahajan, David E. Laughlin e Arthur G. Milnes. "Microstructural characterization of ordered nickel silicide structures grown on (111) nickel silicide films". Journal of Materials Research 11, n. 4 (aprile 1996): 904–11. http://dx.doi.org/10.1557/jmr.1996.0112.

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The formation processes of epitaxial nickel silicides, resulting from the interaction of nickel silicide films (10 nm–100 nm) on (111) silicon (Si) substrates after furnace annealing, have been studied using transmission electron microscopy (TEM) and x-ray diffraction (XRD) techniques. The formation of type-A epitaxial grains (i.e., grown with the same orientation of the underlying Si substrate) and type-B epitaxial grains (i.e., rotated by 180± around the surface normal) in “thick” epitaxial films (i.e., greater than 35 nm) is proposed to be linked to the formation of a fluorite-based CuPt (L11)-like NiSi phase. This phase is found to be a metastable phase and is believed to be a transitional phase toward the formation of the equilibrium NiSi2 phase in both type-A and type-B orientations. In addition, we have found that a fluorite-based CuPt-like NiSi may even coexist with a fluorite-based CuAu I-like structure. The interrelationship between these two structures is discussed in the context of a displacive transformation process in fcc structures as originally proposed by Hansson and Barnes [Acta Metall. 12, 315 (1964)] and Pashley et al. [Philos. Mag. 19, 83 (1969)].

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Le Bail, Armel, Anne-Marie Mercier e Ina Dix. "Sr5(VIVOF5)3F(H2O)3refined from a non-merohedrally twinned crystal". Acta Crystallographica Section E Structure Reports Online 65, n. 6 (23 maggio 2009): i46—i47. http://dx.doi.org/10.1107/s1600536809019126.

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The title compound, pentastrontium tris[pentafluoridooxidovanadate(IV)] fluoride trihydrate, was obtained under hydrothermal conditions. Its crystal structure has been refined from intensity data of a non-merohedrally twinned crystal. Two domains in almost equal proportions are related by a −180° rotation along the reciprocal [101]* vector. The structure may be considered as a derivative of the fluorite structure type, adopted here by SrF2. In the title compound, fluorite-like large rods are recognized, built up from a group of 16 Sr atoms of which 6 are substituted by V atoms, leading to [Sr10V6]∞units. These rods extend infinitely along thebaxis and are interconnected by the three water molecules. Each of the water molecules is shared by two different Sr atoms belonging to two different rods. The rods are also interconnected by an `independent' F atom in a distorted triangular [FSr3] coordination and by hydrogen-bonding interactionsviadonor water molecules. The acceptors are either F atoms or the O atoms of the vanadyl ion, VO2+, that is part of the [VOF5] isolated octahedron.

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Le Bail, A. "Ab initio structure determination of nanosized θ-KAlF4 with edge-sharing AlF6 octahedra". Powder Diffraction 24, n. 3 (settembre 2009): 185–90. http://dx.doi.org/10.1154/1.3194692.

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θ-KAlF4 is a new nanosized potassium tetrafluoroaluminate metastable polymorph (13×18×55 nm3). The crystal structure is solved ab initio from X-ray powder diffraction data in direct space [orthorhombic unit cell with a=8.3242(3) Å, b=7.2502(3) Å, c=11.8875(4) Å, V=717.44(5) Å3, Z=8, and space group Pnma]. This new structure type, unique in the whole AIMIIIF4 family, is related to the fluorite structure and consists of AlF6 octahedra linked via a common edge forming a bioctahedral motif which is trans-connected through the corner-shared fluorine, resulting in the formation of infinite ladderlike double file of octahedra ([Al2F8]2−)n running along the b axis.

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Ling, Christopher D., Ray L. Withers, John G. Thompson e Siegbert Schmid. "Structures of Bi14WO24 and Bi14MoO24 from neutron powder diffraction data". Acta Crystallographica Section B Structural Science 55, n. 3 (1 giugno 1999): 306–12. http://dx.doi.org/10.1107/s0108768198014086.

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The (isomorphous) structures of Bi14WO24, tetradecabismuth tungsten tetracosaoxide, and Bi14MoO24, tetradecabismuth molybdenum tetracosaoxide, have been solved and refined using neutron powder diffraction data in the space group I4/m. The metal-atom array is fully ordered in terms of composition, and in terms of atomic positions deviates only slightly from a fluorite-type δ-Bi2O3-related parent structure. Three independent O-atom sites (accounting for 70 out of 78 O atoms in the unit cell) are also very close to fluorite-type parent positions. The remaining two O-atom sites, which coordinate W, exhibit partial occupancies and displacive disorder, neither of which could be better modelled by lowering of symmetry. The W site is coordinated by four O atoms in highly distorted tetrahedral coordination, the tetrahedron necessarily being orientationally disordered on that site. Nonetheless, the structure appears to be chemically reasonable.

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Scavini, Marco, Mauro Coduri, Mattia Allieta, Paolo Masala, Serena Cappelli, Cesare Oliva, Michela Brunelli, Francesco Orsini e Claudio Ferrero. "Percolating hierarchical defect structures drive phase transformation in Ce1−xGdxO2−x/2: a total scattering study". IUCrJ 2, n. 5 (30 luglio 2015): 511–22. http://dx.doi.org/10.1107/s2052252515011641.

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A new hierarchical approach is presented for elucidating the structural disorder in Ce1−xGdxO2−x/2solid solutions on different scale lengths. The primary goal of this investigation is to shed light on the relations between the short-range and the average structure of these materialsviaan analysis of disorder on the mesocopic scale. Real-space (pair distribution function) and reciprocal-space (Rietveld refinement and microstructure probing) analysis of X-ray powder diffraction data and electron spin resonance (ESR) investigations were carried out following this approach. On the local scale, Gd- and Ce-richdroplets(i.e.small regions a few ångströms wide) form, exhibiting either a distorted fluorite (CeO2) or a C-type (Gd2O3) structure in the whole compositional range. These droplets can then form C-type nanodomains which, for Gd concentrationsxGd≤ 0.25, are embedded in the fluorite matrix. At the site percolation thresholdpCfor a cubic lattice (xGd=pC≃ 0.311), C-type nanodomains percolate inside each crystallite and a structural phase transformation is observed. When this occurs, the peak-to-peak ESR line width ΔHppshows a step-like behaviour, which can be associated with the increase in Gd–Gd dipolar interactions. A general crystallographic rationale is presented to explain the fluorite-to-C-type phase transformation. The approach shown here could be adopted more generally in the analysis of disorder in other highly doped materials.

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Ishizawa, N., Y. Matsushima, M. Hayashi e M. Ueki. "Synchrotron radiation study of yttria-stabilized zirconia, Zr0.758Y0.242O1.879". Acta Crystallographica Section B Structural Science 55, n. 5 (1 ottobre 1999): 726–35. http://dx.doi.org/10.1107/s0108768199005108.

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The fluorite-related cubic structure of yttria-stabilized zirconia, Zr0.75 8Y0.24 2O1.87 9, has been studied by single-crystal X-ray diffraction using synchrotron radiation and by EXAFS. Two diffraction data sets obtained at X-ray energies of 512 and 10 eV below the Y K edge revealed that in the average structure Zr atoms are displaced from the origin of the space group Fm3¯m along 〈111〉 by 0.19 Å, while Y atoms reside at the origin. Approximately 48% of the O atoms occupy the ideal position in the fluorite-type structure, while 43% of O atoms are displaced from the ideal position along 〈001〉 by 0.31 Å. The remaining 9% of O atoms are presumably sited at interstitial positions. Local structures around Zr and Y are investigated by combining the results of single-crystal X-ray diffraction and EXAFS studies.

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Gudat, Axel, Sabine Haag, Rüdiger Kniep e Albrecht Rabenau. "Ternäre Nitride des Lithiums mit den Elementen Cr, Mo und W / Ternary Lithium Nitrides with Elements Cr, Mo and W". Zeitschrift für Naturforschung B 45, n. 2 (1 febbraio 1990): 111–20. http://dx.doi.org/10.1515/znb-1990-0203.

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The ternary compounds were prepared by reaction of the transition metals with Li3N melt under nitrogen. The crystal structures of Li6MeN4 (P42/nmc, Z = 2; Me = Mo: a = 667.3(1) pm, c = 492.5(3) pm; Me = W: a = 667.9(1) pm, c = 492.7(1) pm) and Li15Cr2N9 (P4/ncc, Z = 4; a = 1023.3(5) pm, c = 938.9(7) pm) can be described as fluorite-type superstructures with the lithium and transition metal atoms in tetrahedral holes of the nearly fcc nitrogen arrangement and with an ordered distribution of defects within the cation substructure. In addition, the ternary system Li–Cr–N contains the compound Li6CrN4 with a crystal structure which is not quite clear at present, but which shows close relations to the structures of Li6MeN4 (Me = Mo, W). The previously reported compounds Li9MeN5 (Me = Cr, Mo, W) have not been observed during this study. The respective Cr compound in fact is a nitride-oxide (nitride-imide) of composition Li14Cr2N8(O,NH) with a crystal structure (P3̄, Z = 1, a = 579.9(1) pm, c = 826.3(6) pm) also showing a fluorite-type superstructure.

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Molnár, Zsuzsa, Gabriella B. Kiss, Ferenc Molnár, Tamás Váczi, György Czuppon, István Dunkl, Federica Zaccarini e István Dódony. "Epigenetic-Hydrothermal Fluorite Veins in a Phosphorite Deposit from Balaton Highland (Pannonian Basin, Hungary): Signatures of a Regional Fluid Flow System in an Alpine Triassic Platform". Minerals 11, n. 6 (16 giugno 2021): 640. http://dx.doi.org/10.3390/min11060640.

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The middle Anisian extensional tectonics of the Neotethyan realm developed a small, isolated carbonate platform in the middle part of the Balaton Highland (western Hungary), resulted in the deposition of uranium-bearing seamount phosphorite on the top of the drowned platform and produced some epigenetic fluorite veins in the Middle Triassic sequence. The stable C-O isotope data of carbonates are shifted from the typical Triassic carbonate ranges, confirming the epigenetic-hydrothermal origin of veining. Primary fluid inclusions in fluorite indicate that these veins were formed from low temperature (85–169 °C) and high salinity NaCl + CaCl2 + H2O type (apparent total salinity: 15.91–22.46 NaCl wt%) hydrothermal fluids, similar to parent fluids of the Alpine-type Pb-Zn deposits. These findings indicate that the Triassic regional fluid circulation systems in the Alpine platform carbonates also affected the area of the Balaton Highland. This is also in agreement with the previously established palinspatic tectonic reconstructions indicating that the Triassic carbonate and basement units in the Balaton Highland area were a part of the Southern Alpine. Similar fluorite veining in phosphorite deposits is also known in the Southern Alpine areas (e.g., Monte San Giorgi, Italy). Raman spectroscopic analyses detected H2 gas in the vapor phase of the fluid inclusions and a defect-rich fluorite structure in violet to black colored growth zones. This unique phenomenon is assumed to be the result of interaction between the uranium-rich phosphorite and the parent fluids of the epigenetic fluorite veins.

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24

Hairetdinov, E. "Estimation of conductivity parameters in Sr1 − xThxF2 + 2x solid solution with fluorite-type structure". Solid State Ionics 90, n. 1-4 (settembre 1996): 177–81. http://dx.doi.org/10.1016/s0167-2738(96)00407-9.

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25

Sreena, T. S., P. Prabhakar Rao, Athira K. V. Raj e T. R. Aju Thara. "Exploitation of Eu3+ red luminescence through order–disorder structural transitions in lanthanide stannate pyrochlores for warm white LED applications". Physical Chemistry Chemical Physics 20, n. 37 (2018): 24287–99. http://dx.doi.org/10.1039/c8cp03863e.

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The structural transition from an ordered pyrochlore to a fluorite-type structure in Ln_2.85YSnNbO_10.5:0.15Eu³⁺ (Ln = La, Gd, Y, and Lu) provides a gateway for exploiting Eu³⁺ red luminescence for warm white LED applications.

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26

Fagherazzi, G., P. Canton, A. Benedetti, F. Pinna, G. Mariotto e E. Zanghellini. "Rietveld analysis of the cubic crystal structure of Na-stabilized zirconia". Journal of Materials Research 12, n. 2 (febbraio 1997): 318–21. http://dx.doi.org/10.1557/jmr.1997.0044.

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Abstract (sommario):

Using x-ray Rietveld analysis the fcc (fluorite-type) structure of a Na-containing nanocrystalline zirconia powder (9.5 nm estimated crystallite size) obtained by precipitation and calcination has been confirmed. The result shows that conventional x-ray diffraction techniques can distinguish the cubic crystallographic form of ZrO2 from the tetragonal one in nanosized powders. These conclusions are supported by independent Raman scattering experiments.

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27

Yagi, Yuhji, Jun Satake, Miwa Saito e Hiroshi Yamamura. "Electrode Effects on Dielectric Relaxation in Oxide-Ion Conductor Ce0.7Yb0.3O2-δHaving a Fluorite-Type Structure". Japanese Journal of Applied Physics 50, n. 6R (1 giugno 2011): 065804. http://dx.doi.org/10.7567/jjap.50.065804.

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28

Yagi, Yuhji, Jun Satake, Miwa Saito e Hiroshi Yamamura. "Electrode Effects on Dielectric Relaxation in Oxide-Ion Conductor Ce0.7Yb0.3O2-δHaving a Fluorite-Type Structure". Japanese Journal of Applied Physics 50, n. 6 (20 giugno 2011): 065804. http://dx.doi.org/10.1143/jjap.50.065804.

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29

Newman, R., R. D. Aughterson e G. R. Lumpkin. "Synthesis and Structure of Novel A2BO5 Compounds Containing A = Y, Yb, Gd, Sm, and La and B = Zr, Ti, and Sn". MRS Advances 3, n. 20 (2018): 1117–22. http://dx.doi.org/10.1557/adv.2018.210.

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Abstract (sommario):

With the aim of creating novel ceramics for applications in nuclear materials with high radiation tolerance, multiple samples with A-B-O stoichiometries ranging from 215 to 227 were synthesized and characterized by a combination of SEM, XRD, and TEM methods. Single-phase defect-fluorite-type compounds with A = Sm or Yb and B = Ti, Zr, and/or Sn are reported; whereas, pyrochlore structured compounds and lanthanide sesquioxide phases were found as major phases in numerous samples. A series of Y-b-Sn-O samples was successfully prepared as nearly single phase or single phase materials. These are essentially defect fluorites with extra weak peaks, most likely due to X-ray scattering from oxygen or oxygen and metal cations. We describe some interesting TEM data and describe selected area diffraction patterns with complex modulations.

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30

Kornienko, Oksana, Anatoliy Sameljuk, Olena Andrievskaya, Serhii Yushkevych e Yurii Bataev. "Phase Equilibrium in ZrO2-CeO2-Eu2O3 System at a Temperature of 1500 °C". Recent Progress in Materials 03, n. 03 (24 maggio 2021): 1. http://dx.doi.org/10.21926/rpm.2103036.

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Abstract (sommario):

The phase equilibria and structural transformations in the ternary ZrO2-CeO2-Eu2O3 system at 1500 °C were studied by X-ray diffraction and scanning electron microscopy in the overall concentration range. The system was found to constitute fields of solid solutions based on the tetragonal (Т) modification of ZrО2, cubic (С) and monoclinic (B) modifications of Eu2O3, cubic with a fluorite-type structure (F) modifications of СеО2 (ZrО2), and ordered intermediate phase with a pyrochlore-type structure of Eu2Zr2O7 (Py). The refined lattice parameters of the unit cells corresponding to the solid solutions and microstructures of the definite field of compositions for the systems were determined. The peculiarity of the isothermal section of the phase diagram in the ZrO2-СеO2-Eu2O3 system at 1500 °С is the formation of phase equilibria on the basis of the fluorite solid solutions of ZrO2(CeO2) along with other components. There are at least three homogeneous fields of cubic phases. The isothermal section of the ZrO2-CeO2-Eu2O3 system at 1500 °С was constituted of four three-phase regions (C-Eu2O3 + F-CeO2+Py, C-Eu2O3 + F-ZrO2+Py, Py + F-ZrO2 + T-ZrO2, Py + F-CeO2 + T-ZrO2).

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31

Camprubí, Antoni, Eduardo González-Partida, Antonin Richard, Marie-Christine Boiron, Luis González-Ruiz, César Aguilar-Ramírez, Edith Fuentes-Guzmán, Daniel González-Ruiz e Claire Legouix. "MVT-Like Fluorite Deposits and Oligocene Magmatic-Hydrothermal Fluorite–Be–U–Mo–P–V Overprints in Northern Coahuila, Mexico". Minerals 9, n. 1 (18 gennaio 2019): 58. http://dx.doi.org/10.3390/min9010058.

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Abstract (sommario):

The formation of most fluorite deposits in northern Coahuila (NE Mexico) is explained by MVT models, and is a part of the metallogenic province of northeastern Mexico. However, fluorite skarn deposits also occur in the same region, and there is evidence for late hydrothermal manifestations with no clear origin and evolution. The latter are the main focus of this study; in particular, F–Be–U–Mo–V–P stringers in the Aguachile-Cuatro Palmas area that overprint preexisting fluorite mantos. The region experienced the emplacement of several intrusives during the Eocene and the Oligocene that are collectively grouped into the East Mexico Alkaline Province (EMAP) and postdate MVT-like deposits. Some of these intrusives have associated skarn deposits; most of them are polymetallic, but the unusual El Pilote deposit contains fluorite mineralisation that was remobilised from MVT-like deposits. The formation of the Aguachile deposit (and, collectively, part of the Cuatro Palmas deposit) has been attributed to a shallow retrograde skarn model. The Cuatro Palmas and Las Alicias fluorite deposits consist of MVT-like deposits overprinted by late hydrothermal fluorite mineralisation rich in Be–U–Mo–V–P, and the Aguachile deposit consists entirely of the latter type. The systematic fluid inclusion study of MVT-like, skarn, and late hydrothermal fluorite deposits reveals a very different distribution of temperature and salinity data that allows the discrimination of mineralising fluids for the type of deposit. MVT-like deposits were formed by fluids with temperatures of homogenisation that range between 50 °C and 152 °C and salinities between 5 and 15.5 wt.% NaCl equivalent. The El Pilote fluorite skarn was formed by fluids with temperatures of homogenisation that range between 78 °C and 394 °C and salinities between 5 and 34 wt.% NaCl equivalent, and include CaCl2-rich brines with salinities that range between 24.5 and 29.1 wt.% CaCl2. Late shallow fluorite–Be–U–Mo–V–P hydrothermal deposits were formed by fluids with temperatures of homogenisation that range between 70 °C and 180 °C and salinities between 0.9 and 3.4 wt.% NaCl equivalent; the sole exception to the above is the La Fácil deposit, with salinities that range between 7.9 and 8.8 wt.% NaCl equivalent. While temperatures of homogenisation are similar between MVT-like and late hydrothermal deposits, and both even have hydrocarbon-rich fluid inclusion associations, the salinity of late deposits is similar to that of retrograde skarn fluids, although further diluted. However, homogenisation temperatures tend to be higher in late hydrothermal than in MVT-like deposits, thus making them more similar to retrograde skarn fluids. Although this characteristic cannot solely establish a genetic link between a retrograde skarn model and late hydrothermal deposits in the study area, the characteristics of fluids associated with the latter separate these deposits from those ascribed to an MVT-like model. Assuming that mineralising fluids for late fluorite–Be–U–Mo–V–P hydrothermal deposits may correspond to a retrograde skarn (or “epithermal”) deposit, the source for fluorine may be either from (A) the dissolution of earlier formed MVT-like deposits, (B) the entrainment of remaining F-rich basinal brines, or (C) hydrothermal fluids exsolved from highly evolved magmas. Possibilities A and B are feasible due to a hypothetical situation similar to the El Pilote skarn, and due to the occurrence of hydrocarbon-rich fluid inclusions at the La Fácil deposit. Possibility C is feasible because intrusive bodies related to highly evolved magmas would have provided other highly lithophile elements like Be, U and Mo upon the exsolution of their hydrothermal fluids. Such intrusive bodies occur in both study areas, and are particularly conspicuous at the Aguachile collapse structure.

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32

Ribárik, G., N. Audebrand, H. Palancher, T. Ungár e D. Louër. "Dislocation densities and crystallite size distributions in nanocrystalline ball-milled fluorides,MF2(M= Ca, Sr, Ba and Cd), determined by X-ray diffraction line-profile analysis". Journal of Applied Crystallography 38, n. 6 (12 novembre 2005): 912–26. http://dx.doi.org/10.1107/s0021889805027202.

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Abstract (sommario):

The dislocation densities and crystallite size distributions in ball-milled fluorides,MF2(M= Ca, Sr, Ba and Cd), of the fluorite structure type have been determined as a function of milling time by X-ray diffraction line-profile analysis. The treatment has been based on the concept of dislocation contrast to explain strain anisotropy by means of the modified Williamson–Hall and Warren–Averbach approaches and a whole-profile fitting method using physically based functions. In most cases, the measured and calculated patterns are in perfect agreement; however, in some specific cases, the first few measured profiles appear to be narrower than the calculated ones. This discrepancy is interpreted as the result of an interference effect similar to that described by Rafaja, Klemm, Schreiber, Knapp & Kužel [J. Appl. Cryst.(2004),37, 613–620]. By taking into account and correcting for this interference effect, the microstructure of ball-milled fluorides is determined in terms of dislocation structure and size distributions of coherent domains. A weak coalescence of the crystallites is observed at longer milling periods. An incubation period in the evolution of microstrains is in correlation with the homologous temperatures of the fluorides.

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33

Maki, Ryosuke S. S., e Peter E. D. Morgan. "A further investigation of the complex M3 murataite structure using Hf substitution and STEM-EELS techniques". Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 75, n. 3 (25 maggio 2019): 442–48. http://dx.doi.org/10.1107/s2052520619005419.

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Abstract (sommario):

Many members of the complex crystalline fluorite supercell structures (e.g. zirconolite, pyrochlore and murataite polytypes) have been considered/studied for possible long-term radioactive-waste immobilization. The eight-coordinated sites in these crystals are of particular importance because they are preferred for the accommodation of trivalent rare earths and actinides present in radioactive waste from fuel element processing. The fluorite-type supercell structures include the murataites, M3, M5, M7, M8, having those numbers of repeating fluorite sub-cell units. One simple technique, as shown here, namely the substitution of Hf into the Zr site, is very helpful for structural analysis in these very complex cases in order to further illuminate the site preference of the Zr ion. Three M3 murataite samples, Ca-Mn-Ti-Zr-Al-Fe-O (regular M3), Ca-Ti-Zr-Al-Fe-O (Mn-free M3) and Ca-Mn-Ti-Hf-Al-Fe-O (Hf-substituted M3) are investigated and, through techniques described for larger cells, show that the Zr is very likely not to be hosted in the [6] Ti site in the M3 murataite structure, as suggested by Pakhomova et al. [(2013), Z. Kristallogr. Cryst. Mater. 228, 151–156], but more likely replaces the [8] Ca1 site and less likely the [8] Ca2 site. This adjusted site preference for each cation from the powder X-ray diffraction (PXRD) and scanning transmission electron microscopy electron energy-loss spectroscopy (STEM-EELS) methods, agrees well with the high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image.

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34

Miida, Rokuro, e Michiyoshi Tanaka. "A Modulated Structure in a Fluorite-Type Fast-Ion-Conductor δ-(Bi2O3)1-x(Nb2O5)x". Japanese Journal of Applied Physics 29, Part 1, No. 6 (20 giugno 1990): 1132–38. http://dx.doi.org/10.1143/jjap.29.1132.

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35

Lamas, D. G., R. O. Fuentes, I. O. Fábregas, M. E. Fernández de Rapp, G. E. Lascalea, J. R. Casanova, N. E. Walsöe de Reca e A. F. Craievich. "Synchrotron X-ray diffraction study of the tetragonal–cubic phase boundary of nanocrystalline ZrO2–CeO2synthesized by a gel-combustion process". Journal of Applied Crystallography 38, n. 6 (12 novembre 2005): 867–73. http://dx.doi.org/10.1107/s0021889805025343.

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Abstract (sommario):

The crystal structures of a number of nanocrystalline ZrO2–CeO2solid solutions, synthesized by a pH-controlled nitrate-glycine gel-combustion process, were studied. By using a synchrotron X-ray diffractometer, small peaks of the tetragonal phase, which correspond to forbidden reflections in the case of a perfect cubic fluorite structure, were clearly detected. By monitoring the most intense of these reflections, 112, as a function of the CeO2content, the tetragonal–cubic phase boundary was found to be at 85 (5) mol% CeO2. For a CeO2content up to 68 mol%, a tetragonal phase withc/a> 1 (known as thet′ form) was detected, whereas, between 68 and 85 mol% CeO2, the existence of a tetragonal phase withc/a= 1 and oxygen anions displaced from their ideal positions in the cubic phase (thet′′ form) was verified. Finally, solid solutions with higher CeO2contents exhibit the cubic fluorite-type phase.

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36

Landa-Cánovas, Ángel R., Eladio Vila, Jorge Hernández-Velasco, Jean Galy e Alicia Castro. "Structural elucidation of the Bi2(n + 2)Mo n O6(n + 1) (n = 3, 4, 5 and 6) family of fluorite superstructures by transmission electron microscopy". Acta Crystallographica Section B Structural Science 65, n. 4 (16 luglio 2009): 458–66. http://dx.doi.org/10.1107/s0108768109023908.

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Abstract (sommario):

The cationic framework structure of a whole new family of compounds with the general formula Bi2(n + 2)Mo n O6(n + 1) (n = 3, 4, 5 and 6) has been elucidated by transmission electron microscopy (TEM) methods. High-resolution transmission electron microscopy (HRTEM) has been used to postulate heavy-atom models based on the known structure of the n = 3 phase, Bi10Mo3O24. These models were tested by HRTEM image simulation, electron diffraction and powder X-ray diffraction simulation methods which agreed with the experimental results. The four known phases of this family correspond to n = 3, 4, 5 and 6 members and all show fluorite superstructures. They consist of a common δ-Bi2O3 fluorite-type framework, inside of which are distributed ribbons of {MoO4} tetrahedra which are infinite along b, one tetrahedron thick along c, and of variable widths of 3, 4, 5 or 6 {MoO4} tetrahedra along a depending on the family member (n value). These {MoO4} tetrahedra are isolated, i.e. without sharing any corner as in the [Bi12O14] columnar structural-type phase Bi[Bi12O14][MoO4]4[VO4]. The structure of all these family members can be described as crystallographic shear derivatives from Aurivillius-type phases such as Bi2MoO6, the n = ∞ end member. All these compounds are good oxygen-ion conductors.

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37

Ohtaka, Osamu, Denis Andrault, Pierre Bouvier, Emmanuelle Schultz e Mohamed Mezouar. "Phase relations and equation of state of ZrO2to 100 GPa". Journal of Applied Crystallography 38, n. 5 (15 settembre 2005): 727–33. http://dx.doi.org/10.1107/s0021889805018145.

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Abstract (sommario):

The phase relations and equation of state of ZrO2were investigated up to 100 GPa by means ofin situobservation using laser heating in a diamond anvil cell and synchrotron radiation. A cotunnite (PbCl2)-type phase, which appears above 12.5 GPa, is stable to a pressure of 100 GPa and a temperature of 2500 K. No post-cotunnite phase was observed under the present experimental conditions. The unit-cell parameters and the volumes of the cotunnite-type ZrO2were determined as a function of pressure at room temperature using a laser-annealing technique. The cotunnite-type ZrO2shows rather isotropic compression. The bulk modulus calculated using the Birch–Murnaghan equations of state is 278 GPa, which suggests that high-density ZrO2is a candidate for potentially very hard materials.In situhigh-temperature experiments performed below 12.5 GPa revealed that a tetragonal fluorite (CaF2)-type phase is stable up to 3000 K, although a cubic fluorite-type phase has been assumed to exist in this high-temperature regime. The result suggests the possibility that stoichiometric ZrO2does not show the cubic structure up to the melting temperature.

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38

Gudat, A., R. Kniep e J. Maier. "Ca[(Ni1−xLix)N]: limited solid solutions (0 ⩽ x ⩽ 0.58) in the system Ca[NiN] (Y[CoC]-type structure)-Ca[LiN] (modified fluorite-type structure)". Journal of Alloys and Compounds 186, n. 2 (agosto 1992): 339–45. http://dx.doi.org/10.1016/0925-8388(92)90021-z.

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39

GAMBARDELLA, M. T., B. DOMENGES, T. ROUILLON, M. HERVIEU e B. RAVEAU. "ChemInform Abstract: Introduction of Fluorite Layers in the 1212-Type Structure: The Oxide ( Pb0.5Sr0.5)Sr2Nd2-xCexCu2O9-δ." ChemInform 23, n. 28 (21 agosto 2010): no. http://dx.doi.org/10.1002/chin.199228009.

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40

Sadykov, Vladislav, Ekaterina Sadovskaya, Nikita Eremeev, Elena Pikalova, Nina Bogdanovich, Elena Filonova, Yulia Fedorova, Alexey Krasnov, Pavel Skriabin e Anton Lukashevich. "Design of materials for solid oxide fuel cells cathodes and oxygen separation membranes based on fundamental studies of their oxygen mobility and surface reactivity". E3S Web of Conferences 116 (2019): 00068. http://dx.doi.org/10.1051/e3sconf/201911600068.

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Abstract (sommario):

Design of materials for solid oxide fuel cells cathodes and oxygen separation membranes and studying their oxygen transport characteristics are important problems of modern hydrogen energy. In the current work, fundamentals of such materials design based on characterization of their oxygen mobility by oxygen isotope exchange with C18O2 and 18O2 in flow and closed reactors for samples of Ruddlesden – Popper-type oxides Ln2-xCaxNiO4+δ, perovskite-fluorite nanocomposites PrNi0.5Co0.5O3-δ – Ce0.9Y0.1O2-δ, etc. are presented. Fast oxygen transport was demonstrated for PNC – YDC (DO ~10-8 cm2/s at 700°C) nanocomposites due to domination of the fast diffusion channel involving oxygen of the fluorite phase with incorporated Pr cations and developed perovskite-fluorite interfaces. For LnCNO materials a high oxygen mobility (DO ~10-7 cm2/s at 700°C) provided by the cooperative mechanism of its migration was demonstrated. Depending on Ca dopant content and Ln cation nature, in some cases 1–2 additional channels of the slow diffusion appear due to decreasing the interstitial oxygen content and increasing the energy barrier for oxygen jumps due to cationic size effect. Optimized by the chemical composition and nanodomain structure materials of these types demonstrated a high performance as SOFC cathodes and functional layers in asymmetric supported oxygen separation membranes.

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41

Kornienko, Oksana, Oleksandr Bykov, Аnatoliy Sameliuk e Olena Andrievskaya. "ISOTHERMAL SECTION STRUCTURE THE ZrO2-La2O3-Gd2O3 SYSTEM AT 1500 °С". Ukrainian Chemistry Journal 87, n. 1 (19 febbraio 2021): 23–40. http://dx.doi.org/10.33609/2708-129x.87.01.2021.23-40.

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Abstract (sommario):

Using the methods of physicochemical analysis (XRD, petrography, scanning electron microscopy analyses) phase equilibria were firstly investigated in the ternary system ZrO2–La2O3–Gd2O3 system at 1500 ºС. It was established that in the system there exist fields of solid solutions based on hexagonal (A) modification of La2O3 and cubic with fluorite-type structure (F) and tetragonal (Т) modification ZrО2 , cubic (С) and monoclinic (M) modification Gd2O3 and ordered intermediate phase with pyrochlore-type structure lanthanum zirconate La2Zr2O7 (Py). No new phases were found. The refined lattice parameters of the unit cells for solid solutions for the systems were determined. In the zirconia-rich corner, the solid solutions based on tetragonal modification of ZrO2 are formed. The phase field T-ZrO2 is narrow and elongated (0–18 mol% CeO2) along the ZrO2–CeO2 side of the binary system. The solubility of La2O3 in the T-ZrO2 is low and amounts to ~ 0.5 mol%, as evidenced by XRD analysis results. It is worth noting that the solid solutions based on tetragonal modification of zirconia cannot be quenched from high temperatures due to low stability of T-ZrO2 under cooling with furnace conditions. The diffraction patterns recorded at room temperatures included the peaks of monoclinic phase M-ZrO2. The homogeneity field of solid solution based on A-La2O3 extends to 31 mol% Gd2O3 and 12 mol% ZrO2 in the corresponding binary systems and locates near the composition 6,7 mol % ZrO2–90 mol% La2O3–3.3 mol% Gd2O3 on the section La2O3–(67 mol % ZrO2–33 mol % Gd2O3). It should be noted that the samples with a higher lanthanum oxide content after annealing and cooling rapidly absorb water in humid air and become hydrated. Hence, according to XRD, the hexagonal A-La(OH)3 modification forms instead of the hexagonal A-La2O3 phase. The lattice parameters for A-La(OH)3 phase vary from а = 0.6513 nm, c = 0.3847 nm the sample containing 3.35 mol % ZrО2–95 mol % La2O3–1.65 mol % Gd2O3 to а = 0.6508 nm, c = 0.3847 nm in the two-phase sample (Py+А ) containing 6.7 mol % ZrО2–90 mol % La2O3–3.3 mol % Gd2O3 and to а = 0.6477 nm, c = 0.3725 nm in the three-phase sample (Py+F+А) containing 40.2 mol % ZrО2–40 mol % La2O3–19.8 mol % Gd2O3 The isothermal section of the ZrO2–La2O3–Gd2O3 system at 1500°C contains four three-phase regions (F+Py+A, F+B+A, F+C+B, T+F+Py) and ten two-phase regions (Py+A, A+F, A+B, F+B, B+C, C+F, F+Py, Py+T, T+F, Py+F).

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42

Yang, Z. J., J. Li, R. F. Linghu, X. L. Cheng e X. D. Yang. "Optical and electronic properties of RuO2 from first principles". Canadian Journal of Physics 90, n. 5 (maggio 2012): 441–48. http://dx.doi.org/10.1139/p2012-038.

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Abstract (sommario):

The systematic trends of electronic structure and optical properties of RuO2 consisting of its four phases have been studied by using norm-conserving pseudopotential within the generalized gradient approximation for the exchange–correlation potential. The total density of states (DOS) and energy band structure investigations revealed that the fluorite phase possesses the broadest conduction bandwidth (0–30 eV) and the pyrite phase possesses the narrowest conduction bandwidth (0–5 eV). Study on partial DOS we found that O 2p electrons of the fluorite phase present a significant shift towards the Fermi level and Ru s and p electrons of the rutile phase contribute little to the orbital energy level formation. For the first time, we found that the norm-conserving pseudopotential failed to obtain the normal DOS and energy band distributions for a rutile Ru atom below about –40 eV, whereas such missing electronic distributions could be obtained successfully using an ultrasoft pseudo potential. Investigations on the optical properties further found that the rutile and CaCl2-type phases behave more similarly and the fluorite phase shows the most sensitive response in the whole radiation reaction region. The electron energy loss function revealed that the pyrite phase corresponds to the least relative intensity.

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43

Matovic, B., J. Dukic, A. Devecerski, S. Boskovic, M. Ninic e Z. Dohcevic-Mitrovic. "Crystal structure analysis of Nd-doped ceria solid solutions". Science of Sintering 40, n. 1 (2008): 63–68. http://dx.doi.org/10.2298/sos0801063m.

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This paper deals with Nd-doped ceria solid solutions: Ce1-xNdxO2-d with "x" ranging from 0 to 0.25. Six different powders were synthesized by applying the method based on selfpropagating room temperature reaction (SPRT) between metallic nitrates and sodium hydroxide. The method is known to assure very precise stoichiometry of the final product in comparison with a tailored composition. Rietveld refinement was employed to get structural information on the synthesized powder. An increase of Nd ion concentration increases the unit cell parameters and average bond distances. We have shown that all obtained powders were solid solutions with a fluorite-type crystal structure and all powder particles were of nanometric size (about 3 nm).

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Мещерских, А. Н., А. А. Кольчугин, Б. Д. Антонов e Л. А. Дунюшкина. "Фазовый состав, микроструктура и электропроводность твердых электролитов HfO_2-R-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=- (R=Sc, Y, Ho, Er, Tm, Yb, Lu)". Физика твердого тела 62, n. 1 (2020): 145. http://dx.doi.org/10.21883/ftt.2020.01.48752.557.

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Abstract (sommario):

The effect of the addition of 11 mol % R2O3 (R = Sc, Y, Ho, Er, Tm, Yb, Lu) on the phase and elemental composition, microstructure, and electrical conductivity of hafnium oxide was studied. When all additives, with the exception of scandium, are introduced into HfO2, solid solutions with a cubic structure such as fluorite are formed. The HfO2-Sc2O3 sample is an Hf7Sc2O17 phase having a fluorite-type lattice with rhombohedral distortions that undergoes reversible changes in the cubic structure at a temperature of ~ 760 ° C. It has been established that the nature of the dopant practically does not affect the microstructure of the HfO2-R2O3 ceramics; all samples are coarse-grained with a grain size of up to 10 μm. It was shown that the conductivity of HfO2-R2O3 samples is determined by the volume of grains. The most promising materials for use as a solid oxide electrolyte are HfO2-Tm2O3 and HfO2-Yb2O3, in which high conductivity is combined with structural stability.

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45

Gnanam, S., e V. Rajendran. "Influence of Various Surfactants on Size, Morphology, and Optical Properties of CeO2 Nanostructures via Facile Hydrothermal Route". Journal of Nanoparticles 2013 (26 marzo 2013): 1–6. http://dx.doi.org/10.1155/2013/839391.

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Different surfactants such as sodium dodecyl sulfate (SDS), polyethylene glycol (PEG), and cetyltrimethyl ammonium bromide (CTAB,) assisted cerium oxide (CeO2) nanoparticles were synthesized by using cerium chloride and potassium hydroxide as the starting materials via facile hydrothermal route. The powder X-ray diffraction (XRD) shows that cubic fluorite-type structure of pure CeO2 and the average crystallite sizes were calculated to be ~12–16 nm. Raman spectra of various surfactants assisted CeO2 consist of a single triply degenerated F2g mode characteristic of the fluorite structure. The elongated spherical-like morphology of SDS assisted CeO2 samples was observed from the SEM and TEM studies. Optical absorption spectra showed a blue shift by the capped CeO2 due to the quantum confinement effect. Photoluminescence (PL) emission studies shows that there is a change in the intensity of emission peaks by the capping agents, which indicates that the capping layers did result in size changes or increased surface defect.

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Zaitsev, A. N., A. R. Chakhmouradian, O. I. Siidra, J. Spratt, C. T. Williams, C. J. Stanley, S. V. Petrov, S. N. Britvin e E. A. Polyakova. "Fluorine-, yttrium- and lanthanide-rich cerianite-(Ce) from carbonatitic rocks of the Kerimasi volcano and surrounding explosion craters, Gregory Rift, northern Tanzania". Mineralogical Magazine 75, n. 6 (dicembre 2011): 2813–22. http://dx.doi.org/10.1180/minmag.2011.075.6.2813.

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AbstractCerianite-(Ce), ideally CeO2, occurs as rounded grains up to 5 μm across in a block of highly altered calcite carbonatite lava from the Kerimasi volcano, and as euhedral crystals up to 200 μm across in carbonatite-derived eluvial deposits in the Kisete and Loluni explosion craters in the Gregory Rift, northern Tanzania. X-ray powder diffraction data (a = 5.434(5) Å) and Raman spectroscopy (minor vibration modes at 184 and 571 cm—1 in addition to a strong signal at 449 cm—1) suggest the presence of essential amounts of large cations and oxygen vacancies in the Kisete material. Microprobe analyses reveal that the mineral contains both light and heavy trivalent rare earth elements (REE) (7.9-15.5 wt.% LREE2O3 and 4.9-9.7 wt.% HREE2O3), and that it is enriched in yttrium (7.1 — 14.5 wt.% Y2O3) and fluorine (2.2—3.5 wt.%). Single-crystal structure refinement of the mineral confirms a fluorite-type structure with a cation—anion distance of 2.3471(6) Å. The cerianite-(Ce) is considered to be a late-stage secondary mineral in the carbonatitic rocks.

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Spinolo, G., e C. Tomasi. "Fluorite-related phases in the Bi-rich part of the Bi,Mo/O system". Powder Diffraction 12, n. 1 (marzo 1997): 16–19. http://dx.doi.org/10.1017/s0885715600009374.

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Two compounds with compositions around n=14 and n∼5.4 (n=Bi/Mo molar ratio) have been prepared by solid-state reaction with five heating/grinding cycles at 800 °C. The lattice constants of both compounds can be related to the fluorite-type structure of δ-Bi2O3. Bi14MoO24 has been indexed as an orthorhombic pseudotetragonal (√2×√2×1) superstructure: a=7.812 (±0.005) Å, b=7.762 (±0.005) Å, c=5.7716 (±0.0007) Å (but a+b=15.5750±0.0020). For orthorhombic (3×5×3) Bi38Mo7O78: a=16.8236 (±0.0027) Å, b=28.6182 (±0.0045) Å, c=16.9082 (±0.0027) Å.

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48

SONI, B., e S. BISWAS. "CERIA NANOPARTICLES SYNTHESIZED BY A POLYMER PRECURSOR METHOD". International Journal of Modern Physics: Conference Series 22 (gennaio 2013): 169–72. http://dx.doi.org/10.1142/s2010194513010076.

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We report a novel synthesis technique of ceria nanoparticles by a sol-gel type chemical process using poly-vinyl alcohol (PVA) as a capping as well as a reducing agent. The as-synthesized CeO 2 nanoparticles were characterized by X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM). The XRD analysis reveals the fluorite type face centered cubic structure in the ceria nanoparticles with an average crystallite size of 6 nm and 9 nm for the samples calcined at 350°C and 400°C, respectively.

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Jucha, S., G. Moskal e M. Mikuśkiewicz. "Synthesis and Characterization of Thermal Properties of Type Eu2O3-ZrO2 Sinters". Archives of Metallurgy and Materials 61, n. 2 (1 giugno 2016): 1121–28. http://dx.doi.org/10.1515/amm-2016-0188.

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Abstract The oxides with pyrochlore or defected fluorite structure are a potential alternative ceramic materials for now widely used yttria-stabilized zirconia 8YSZ in the application for the insulation layer of thermal barrier coatings systems. This paper presents a procedure of synthesis of europium zirconate of Eu2Zr2O7 type, by the method of high temperature sintering under pressure. The analysis of the effect of the powders` homogenization methods on homogeneity of final sintered material showed that the highest homogeneity can be obtained after mechanical mixing in alcohol. Moreover, the DSC investigation carried out on a mixture of powders before the sintering process and on the material after high temperature sintering under pressure, suggest the synthesis of a new phase an europium zirconate Eu2Zr2O7 with the pyrochlore structure. Obtained phase was characterized by stability over the entire range of tested temperature, i.e. to 1450°C. The resulting material based on europium zirconate has a lower coefficient of thermal diffusivity than the now widely used 8YSZ.

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Slobodyuk, A. B., V. Ya Kavun, N. F. Uvarov, E. B. Merkulov e M. M. Polyantsev. "NMR and complex impedance study of ionic motion in new Rb0.4Bi0.6–In F2.2 solid solutions with fluorite-type structure". Solid State Ionics 360 (febbraio 2021): 115545. http://dx.doi.org/10.1016/j.ssi.2020.115545.

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