Crichtonite Structure Type (Am21O38 and A2M19O36) as a Host Phase in Crystalline Waste Form Ceramics

1994 ◽  
Vol 353 ◽  
Author(s):  
W. L. Gong ◽  
R. C. Ewing ◽  
L. M. Wang ◽  
H. S. Xie
Keyword(s):  
Fission Products ◽  
Structure Type ◽  
Reaction Products ◽  
Charge Balance ◽  
X Ray Diffraction ◽  
Natural Minerals ◽  
Naturally Occurring ◽  
A Site ◽  
Multi Phase ◽  
Cation Sites

AbstractPrevious studies of ceramic crystalline waste forms, e.g. Synroc, tailored ceramics, and supercalcine, have concentrated on phases which are major constituents in the formulations: zirconolite, pyrochlore, hollandite, perovskite and zircon. These phases usually occur as members of multi-phase assemblages which are required for the incorporation of the wide variety of radionuclide elements present in the waste and the non-radioactive components added during reprocessing and pretreatment. The crichtonite structure (AM21O38 and A2M19O36), based on crystallo-chemical considerations and natural compositional analogues, may effectively incorporate both fission products and actinides. The naturally occurring crichtonite structure types include Sr (crichtonite), Ca and REE (loveringite), Na (landauite), REE and U (davidite), K (mathiasite), Ba (lindsleyite), and Pb (senaite), which are classified based on the dominant, large cations occupying the A-site. The crystal structure contains three types of sites of distinct size, from very large, M0, intermediate (M1, M3, M4, and M5), to small (M2). Numerous coupled substitutions within these cation sites allow for charge balance. Synthesis experiments were completed on the Ba-, Sr-, Ca-, and K-member compositions at 3 GPa and 1,150 °C. Low pressure synthesis should be possible, as natural minerals mostly occur in low-P systems. Reaction products were characterized by powder x-ray diffraction, scanning electron microscopy and electron microprobe analysis. In addition to the crichtonite phases, rutile, spinel, perovskite and armalcolite were identified as well. The Crichtonite structure type is estimated to accommodate waste loading of up to 30 wt. % PW-4B waste.

scholarly journals Synthesis and superstructural characterization of Fe1.89Mo4.11O7

1994 ◽  
Vol 9 (4) ◽  
pp. 891-897 ◽  
Author(s):  
George L. Schimek ◽  
Robert E. McCarley ◽  
L. Scott Chumbley
Keyword(s):  
Structure Type ◽  
Tetrahedral Coordination ◽  
X Ray Diffraction ◽  
Cation Site ◽  
X Ray ◽  
Transmission Electron ◽  
The Family ◽  
Regular Arrangement ◽  
Cation Sites

Superstructuring in the new compound Fe1.89Mo4.11O7 has been elucidated by transmission electron microscopy. This compound is a member of the family M2MO4O7 and has both iron and molybdenum atoms occupying octahedrally coordinated sites in the structure, represented by Fet(Fe0.89M0.11)0Mo4O7. The superstructuring, detected only by electron diffraction, involved tripling of all three lattice parameters of the subcell. The subcell was structured by single crystal x-ray diffraction [Imma, no. 74, a = 5.9793(5) Å, b = 5.7704(4) Å, and c = 17.036(1) Å]. This structure type contains a close-packed arrangement of Mo4O7 units, which are infinite chains of trans edge-shared molybdenum octahedra running parallel to b*. Two different coordination environments are observed for the cations. Parallel to the a* direction, infinite edge-sharing MO6 (M = 89% Fe or 11% Mo) octahedra are observed. The second cation site, with nearly tetrahedral coordination by oxygen, is filled solely by iron. The superstructure can be rationalized by a regular arrangement of iron and molybdenum atoms in the octahedrally coordinated cation sites.

The mineralogy of the historical Mochalin Log REE deposit, South Urals, Russia. Part II. Radekškodaite-(La), (CaLa5)(Al4Fe2+)[Si2O7][SiO4]5O(OH)3 and radekškodaite-(Ce), (CaCe5)(Al4Fe2+)[Si2O7][SiO4]5O(OH)3, two new minerals with a novel structure-type belonging to the epidote–törnebohmite polysomatic series

2020 ◽  
pp. 1-15
Author(s):  
Anatoly V. Kasatkin ◽  
Natalia V. Zubkova ◽  
Igor V. Pekov ◽  
Nikita V. Chukanov ◽  
Dmitriy A. Ksenofontov ◽  
...  
Keyword(s):  
Czech Republic ◽  
Structure Type ◽  
Associate Professor ◽  
South Urals ◽  
Charge Balance ◽  
X Ray Diffraction ◽  
Unit Cell Parameters ◽  
X Ray ◽  
Cell Parameters ◽  
Novel Structure

Abstract Two new isostructural minerals radekškodaite-(La) (CaLa5)(Al4Fe2+)[Si2O7][SiO4]5O(OH)3 and radekškodaite-(Ce) (CaCe5)(Al4Fe2+)[Si2O7][SiO4]5O(OH)3 were discovered in polymineralic nodules from the Mochalin Log REE deposit, South Urals, Russia. Radekškodaite-(La) is associated with allanite-(Ce), allanite-(La), bastnäsite-(Ce), bastnäsite-(La), ferriallanite-(Ce), ferriallanite-(La), ferriperbøeite-(La), fluorbritholite-(Ce), törnebohmite-(Ce) and törnebohmite-(La). Radekškodaite-(Ce) is associated with ancylite-(Ce), bastnäsite-(Ce), bastnäsite-(La), lanthanite-(La), perbøeite-(Ce) and törnebohmite-(Ce). The new minerals form isolated anhedral grains up to 0.35 × 0.75 mm [radekškodaite-(La)] and 1 mm × 2 mm [radekškodaite-(Ce)]. Both minerals are greenish-brown with vitreous lustre. Dcalc = 4.644 [radekškodaite-(La)] and 4.651 [radekškodaite-(Ce)] g cm–3. Both minerals are optically biaxial (+); radekškodaite-(La): α = 1.790(7), β = 1.798(5), γ = 1.825(8) and 2Vmeas = 60(10)°; radekškodaite-(Ce): α = 1.798(6), β = 1.806(6), γ = 1.833(8) and 2Vmeas = 65(10)°. Chemical data [wt.%, electron-microprobe; FeO:Fe2O3 by charge balance; H2O by stochiometry; radekškodaite-(La)/radekškodaite-(Ce)] are: CaO 3.40/2.74, La2O3 27.68/22.23, Ce2O3 20.39/24.30, Pr2O3 0.94/1.48, Nd2O3 1.71/3.18, ThO2 0.23/0.24, MgO 0.85/1.04, Al2O3 10.35/10.84, MnO 0.64/0.69, FeO 2.55/2.76, Fe2O3 3.12/2.57, TiO2 0.13/0.04, SiO2 26.03/26.10, F 0.10/0.09, H2O 1.62/1.63, –O=F –0.04/–0.04, total 99.70/99.89. The empirical formulae based on O28(OH,F)3 are: radekškodaite-(La): (Ca0.98Th0.01La2.75Ce2.01Nd0.16Pr0.09)Σ6.00(Al3.28Fe3+0.63Fe2+0.57Mg0.34Mn0.15Ti0.03)Σ5.00Si7.00O28[(OH)2.91F0.09]; radekškodaite-(Ce): (Ca0.79Mn0.16Th0.01Ce2.39La2.20Nd0.30Pr0.14)Σ5.99(Al3.43Fe2+0.62Fe3+0.52Mg0.42Ti0.01)Σ5.00Si7.00O28[(OH)2.92F0.08]. Both minerals are monoclinic, P21/m; the unit-cell parameters [radekškodaite-(La)/radekškodaite-(Ce)] are: a = 8.9604(3)/8.9702(4), b = 5.7268(2)/5.7044(2), c = 25.1128(10)/25.1642(13) Å, β = 116.627(5)/116.766(6)°, V = 1151.98(7)/1149.68(11) Å3 and Z = 2/2. The crystal structures are solved based on single-crystal X-ray diffraction data; R = 0.0554 [radekškodaite-(La)] and 0.0769 [radekškodaite-(Ce)]. Both minerals belong to the epidote–törnebohmite polysomatic series and represent first members of ET2-type: their structure consists of regular alternating modules, one slab of the epidote (E) structure and two slabs of törnebohmite (T). The rootname radekškodaite is given in honor of the Czech mineralogist Radek Škoda (born 1979), Associate Professor at Masaryk University, Brno, Czech Republic. The suffix-modifier -(La) or -(Ce) indicates the predominance of La or Ce among REE in the mineral.

High Temperature XRD Studies of Selected Carbonate Minerals

1984 ◽  
Vol 28 ◽  
pp. 331-338 ◽  
Author(s):  
S. S. Iyengar ◽  
P. Engler ◽  
M. W. Santana ◽  
E. R. Wong
Keyword(s):  
High Temperature ◽  
Thermal Behavior ◽  
Reaction Products ◽  
X Ray Diffraction ◽  
In Situ Xrd ◽  
Natural Minerals ◽  
High Temperature Xrd ◽  
Analytical Reagent ◽  
Thermal Analysis Techniques

Thermal analysts have exploited the sensitivity of carbonate mineral decomposition to furnace atmosphere as a diagnostic tool for identifying and quantifying these minerals in mixtures and solid solutions (1-3). However, thermal analysis techniques alone cannot reveal information about the reaction products after each thermal event. In-situ high temperature x-ray diffraction is one technique that can identify these products. Using this technique, Kissinger et al. (4) identified the reaction products of the thermal decomposition of reagent grade FeCO3 (siderite) and MgCO3 (magnesite). However, the thermal behavior of analytical reagent grade carbonates differs from natural minerals (1). Milodowski and Morgan (5) used in-situ XRD to investigate the thermal behavior of the dolomite-ankerite series.

Lanthanum tetrazinc, LaZn4

2012 ◽  
Vol 68 (6) ◽  
pp. i37-i40 ◽  
Author(s):  
Igor Oshchapovsky ◽  
Volodymyr Pavlyuk ◽  
Grygoriy Dmytriv ◽  
Alexandra Griffin
Keyword(s):  
Rare Earth ◽  
Diffraction Data ◽  
Alkaline Earth ◽  
Earth Metal ◽  
Structure Type ◽  
Alkaline Earth Metal ◽  
X Ray Diffraction ◽  
X Ray ◽  
A Site ◽  
First Time

The structure of lanthanum tetrazinc, LaZn4, has been determined from single-crystal X-ray diffraction data for the first time, approximately 70 years after its discovery. The compound exhibits a new structure type in the space groupCmcm, with one La atom and two Zn atoms occupying sites withm2msymmetry, and one Zn atom occupying a site with 2.. symmetry. The structure is closely related to the BaAl4, La3Al11, BaNi2Si2and CaCu5structure types, which can be presented as close-packed arrangements of 18-vertex clusters, in this case LaZn18. The kindred structure types contain related 18-vertex clusters around atoms of the rare earth or alkaline earth metal.

Strontium Ruthenate Perovskites with High Specific Capacitance for use in Electrochemical Capacitors

1997 ◽  
Vol 496 ◽  
Author(s):  
P. M. Wilde ◽  
T. J. Guther ◽  
R. Oesten ◽  
J. Garche
Keyword(s):  
Active Sites ◽  
Metal Salt ◽  
High Specific Capacitance ◽  
Amorphous Structure ◽  
Charge Balance ◽  
X Ray Diffraction ◽  
New Synthesis ◽  
Capacitive Properties ◽  
A Site ◽  
Similar Phase

ABSTRACTStrontium ruthenates with the perovskite type structure ABO3 have been shown to exhibit attractive capacitive properties. Doping on the A site with La lead to typical capacitance values of 21 F/g. These materials were synthesized by coprecipitating metal hydroxides from a stoichiometric salt solution and subsequent firing at 800 °C in air. In this paper we present a new procedure to synthesize the materials which are crystalline and nevertheless show appreciable capacitances in contrast to ruthenium dioxide material, which only works in a hydrated amorphous structure. The process basically consists in a pyrolysis of concentrated metal salt solutions of the respective chlorides and nitrates at 500 °C for several minutes. Excess soluble phases are removed by washing out with water. X-ray diffraction experiments revealed similar phase purity and crystallinity as known from the coprecipitated materials. However the measured capacitances of undoped perovskites reached high values of 200 F/g exceeding twenty times the value of respective coprecipitated materials. First experiments on doping the materials promise further progress. The new synthesis route introduces a higher surface area by leaving cavities from leached soluble phases and bulk defects into the crystal structure. The first effect increases the number of active sites in contact with the electrolyte while the latter enhances the protonie conduction which is necessary to keep the charge balance within the material during cycling.

The structure of H3O+-exchanged pharmacosiderite

2010 ◽  
Vol 74 (3) ◽  
pp. 487-492 ◽  
Author(s):  
S. J. Mills ◽  
S. L. Hager ◽  
P. Leverett ◽  
P. A. Williams ◽  
M. Raudsepp
Keyword(s):  
Crystal Structure ◽  
United Kingdom ◽  
Single Crystal ◽  
Alkali Metals ◽  
Structure Type ◽  
Sensu Stricto ◽  
X Ray Diffraction ◽  
X Ray ◽  
Hydronium Ion ◽  
A Site

AbstractThe crystal structure of H3O+-exchanged pharmacosiderite (pharmacosiderite is KFe4(AsO4)3(OH)4·nH2O, sensu stricto) has been determined by single-crystal X-ray diffraction and refined to R1 = 0.0418. H3O+-exchanged pharmacosiderite, (H3O+)Fe4(AsO4)3(OH)4·4.5H2O, is cubic, space group Pm, with a = 7.982(9) Å, V = 508.5(9) Å3 and Z = 1. The structure broadly conforms to that of the general pharmacosiderite structure type, with the hydronium ion generated by partial protonation of a site corresponding to a molecule of water of crystallization and its symmetry-related equivalents. In addition, the structure of a “pharmacosiderite” from Cornwall, United Kingdom, in which no alkali metals could be detected, has been re-evaluated and found to be consistent with that of the H3O+- exchanged structure. Its composition is (H3O+)Fe4(AsO4)3(OH)4·4H2O, with the partially occupied water found for the exchanged structure at (½, ½, ½) being absent in this case.

M+M3+2As(HAsO4)6and α- and β-M+M3+(HAsO4)2(M+M3+= RbAl or CsFe): six new compounds crystallizing in three closely related structure types

2018 ◽  
Vol 74 (6) ◽  
pp. 721-727 ◽  
Author(s):  
Karolina Schwendtner ◽  
Uwe Kolitsch
Keyword(s):  
Single Crystal ◽  
Crystal Structures ◽  
General Formula ◽  
Structure Type ◽  
Group Symmetry ◽  
Charge Balance ◽  
X Ray Diffraction ◽  
X Ray ◽  
Stacking Order ◽  
New Compounds

The crystal structures of hydrothermally synthesized (T= 493 K, 7–9 d) rubidium aluminium bis[hydrogen arsenate(V)], RbAl(HAsO4)2, caesium iron bis[hydrogen arsenate(V)], CsFe(HAsO4)2, rubidium dialuminium arsenic(V) hexakis[hydrogen arsenate(V)], RbAl2As(HAsO4)6, and caesium diiron arsenic(V) hexakis[hydrogen arsenate(V)], CsFe2As(HAsO4)6, were solved by single-crystal X-ray diffraction. The four compounds with the general formulaM+M3+(HAsO4)2adopt the RbFe(HPO4)2structure type (R\overline{3}c) and a closely related new structure type, which is characterized by a different stacking order of the building units, leading to noncentrosymmetric space-group symmetryR32. The second new structure type, with the general formulaM+M3+2As(HAsO4)6(R\overline{3}c), is also a modification of the RbFe(HPO4)2structure type, in which one third of theM3+O6octahedra are replaced by AsO6octahedra, and two thirds of the voids in the structure, which are usually filled byM+cations, remain empty to achieve charge balance.

scholarly journals Th-rich loparite from the Khibina alkaline complex, Kola Peninsula: isomorphism and paragenesis

1998 ◽  
Vol 62 (3) ◽  
pp. 341-353 ◽  
Author(s):  
Roger H. Mitchell ◽  
Anton R. Chakhmouradian
Keyword(s):  
Infrared Transmission ◽  
X Ray Diffraction ◽  
Alkaline Complex ◽  
X Ray ◽  
Naturally Occurring ◽  
Accessory Phase ◽  
Diffraction Patterns ◽  
A Site ◽  
Perovskite Type ◽  
Low Symmetry

AbstractTh-rich (up to 18.4 wt% ThO2) loparite occurs as an accessory phase in foyaite pegmatites at Mt. Eveslogchorr, Khibina complex, Russia. It is associated with aegirine, astrophyllite, eudialyte, lorenzenite, lamprophyllite, magnesio-arfvedsonite and gerasimovskite. Loparite crystals are zoned from niobian loparite (core) to niobian thorian and thorian niobian loparite (rim). Th-enrichment is accompanied by a decrease in Na, LREE, Sr and increase in A-site vacancies. The most Th-rich composition approaches (Na0.39LREE0.19Th0.12Ca0.05Sr0.02)Σ0.77(Ti0.76Nb0.27)Σ1.03O3. The mineral is partly or completely metamict and after annealing gives an X-ray diffraction powder pattern similar to that of synthetic NaLaTi2O6 and naturally occurring loparite of different composition. For the Th-rich rim sample, the five strongest diffraction lines (Å) are: 2.72 (100) 110, 1.575 (60) 211, 1.925 (40), 1.368 (30) 220, 1.222 (20) 310; a = 3.867(2) Å. The X-ray diffraction patterns do not exhibit peak splitting or other diffraction lines typical of low-symmetry and ordered perovskite-type structures. Composition determinations, infrared transmission spectroscopy and X-ray diffractometry show that thorian loparite is partly replaced by betafite with LREE and Th as dominant A-site cations (‘ceriobetafite’). Some loparite samples also exhibit thin replacement mantles of belyankinite with high LREE2O3 and ThO2 contents. Both ‘ceriobetafite’ and belyankinite were formed due to metasomatic alteration of loparite.

scholarly journals Two new Rb–Ga arsenates: RbGa(HAsO4)2 and RbGa2As(HAsO4)6

2018 ◽  
Vol 74 (9) ◽  
pp. 1244-1249 ◽  
Author(s):  
Karolina Schwendtner ◽  
Uwe Kolitsch
Keyword(s):  
Single Crystal ◽  
Crystal Structures ◽  
Structure Type ◽  
Charge Balance ◽  
X Ray Diffraction ◽  
X Ray

The crystal structures of hydrothermally synthesized (T = 493 K, 7–9 d) rubidium gallium bis[hydrogenarsenate(V)], RbGa(HAsO4)2, and rubidium digallium arsenic(V) hexa[hydrogenarsenate(V)], RbGa2As(HAsO4)6, were solved by single-crystal X-ray diffraction. Both compounds have tetrahedral–octahedral framework topologies. The M + cations are located in channels of the respective framework. RbGa(HAsO4)2 crystallizes in the RbFe(HPO4)2 structure type (R\overline{3}c), while RbGa2As(HAsO4)6 adopts the structure type of RbAl2As(HAsO4)6 (R\overline{3}c), which represents a modification of the RbFe(HPO4)2 structure type. In this modification, one third of the M 3+O6 octahedra are replaced by AsO6 octahedra, and two thirds of the voids in the structure, which are usually filled by M + cations, remain empty to achieve charge balance.

High Resolution Replication of Organoclay Surfaces

1982 ◽  
Vol 40 ◽  
pp. 576-577
Author(s):  
W. W. Barker ◽  
W. E. Rigsby ◽  
V. J. Hurst ◽  
W. J. Humphreys
Keyword(s):  
Clay Mineral ◽  
Organic Molecule ◽  
Organic Molecules ◽  
X Ray Diffraction ◽  
Xrd Pattern ◽  
X Ray ◽  
Naturally Occurring ◽  
Silicate Layers ◽  
Mineral Identification

Experimental clay mineral-organic molecule complexes long have been known and some of them have been extensively studied by X-ray diffraction methods. The organic molecules are adsorbed onto the surfaces of the clay minerals, or intercalated between the silicate layers. Natural organo-clays also are widely recognized but generally have not been well characterized. Widely used techniques for clay mineral identification involve treatment of the sample with H2 O2 or other oxidant to destroy any associated organics. This generally simplifies and intensifies the XRD pattern of the clay residue, but helps little with the characterization of the original organoclay. Adequate techniques for the direct observation of synthetic and naturally occurring organoclays are yet to be developed.

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