Precession Photographs Research Articles

U1.33T4Al8Si2 (T = Ni, Co): Complex Uranium Silicides Grown from Aluminum/Gallium Flux Mixtures.

Two new quaternary analogs of the Gd1+xFe4Si10-y structure type were grown from the reaction of uranium, silicon, and a transition metal (nickel or cobalt) in an excess of aluminum/gallium flux. The use of a mixed flux was found to be necessary for the formation of U1.33T4Al8Si2 (T = Ni, Co). Single crystal X-ray diffraction data shows the presence of disordered U/Si layers that are characteristic of this structure type; precession photographs indicate partial formation of a superstructure and stacking disorder along the c-axis. This disorder may be the cause of the spin glass behavior that is particularly evident in the nickel analog, which exhibits a spin freezing transition at TF = 7 K. These compounds are resistant to chemical attack and oxidation and may be potential waste forms.

Redetermination of metarossite, CaV5+2O6·2H2O.

The crystal structure of metarossite, ideally CaV2O6·2H2O [chemical name: calcium divanadium(V) hexa-oxide dihydrate], was first determined using precession photographs, with fixed isotropic displacement parameters and without locating the positions of the H atoms, leading to a reliability factor R = 0.11 [Kelsey & Barnes (1960 ▸). Can. Mineral.6, 448-466]. This communication reports a structure redetermination of this mineral on the basis of single-crystal X-ray diffraction data of a natural sample from the Blue Cap mine, San Juan County, Utah, USA (R1 = 0.036). Our study not only confirms the structural topology reported in the previous study, but also makes possible the refinement of all non-H atoms with anisotropic displacement parameters and all H atoms located. The metarossite structure is characterized by chains of edge-sharing [CaO8] polyhedra parallel to [100] that are themselves connected by chains of alternating [VO5] trigonal bipyramids parallel to [010]. The two H2O mol-ecules are bonded to Ca. Analysis of the displacement parameters show that the [VO5] chains librate around [010]. In addition, we measured the Raman spectrum of metarossite and compared it with IR and Raman data previously reported. Moreover, heating of metarossite led to a loss of water, which results in a transformation to the brannerite-type structure, CaV2O6, implying a possible dehydration pathway for the compounds M2+V2O6·xH2O, with M = Cu, Cd, Mg or Mn, and x = 2 or 4.

Synthesis of large and homogeneous single crystals of water-bearing minerals by slow cooling at deep-mantle pressures

The presence of water in the Earth’s deep mantle is an issue of increasing interest in the field of highpressure mineralogy. An important task for further advancing research in the field is to create homogeneous single crystals of candidate deep-mantle water-bearing minerals of 1 mm or larger in size, which is required for applying them for the time-of-flight (TOF) single-crystal Laue diffraction method with a third-generation neutron instrument. In this study, we perform several experiments to demonstrate an improved methodology for growing hydrous crystals of such large sizes at relevant transition zone and lower-mantle conditions via very slow cooling over a maximum period of 1 day. Successfully synthesized crystals using this methodology include dense hydrous magnesium silicate (DHMS) phase E, hydrous wadsleyite, hydrous ringwoodite, and bridgmanite (silicate perovskite). It is also demonstrated that these hydrous crystals can be grown from deuterium enriched starting materials in addition to those having a natural hydrogen isotope ratio. Magnitudes of chemical and crystallographic heterogeneities of the product crystals were characterized by comprehensive analysis of X-ray precession photography, single-crystal X-ray diffraction (SCXRD), field-emission scanning electron microscope (FE-SEM), electron probe microanalyzer (EPMA), secondary ion mass spectroscopy (SIMS), powder X-ray diffraction (PXRD), and TOF neutron powder diffraction (TOF-NPD). The product crystals were confirmed to be inclusion free and crystallographically homogeneous. Compositional and isotopic differences of major elements and hydrogen isotope abundances were lower than 1 and 3%, respectively, among intracrystals and intercrystals within each recovered sample capsule. Phase E crystals up to 600 μm in the largest dimension were grown at a constant temperature of 1100 °C kept for 3 h. Using a lattice parameter-to-temperature relation of phase E, the thermal gradient in the sample capsules for the phase E synthesis has been evaluated to be 20 °C/mm. Hydrous wadsleyite crystals up to 1100 μm in the largest dimension were grown at 1390 °C with a temperature reduction of 70 °C during heating for 10 h. Hydrous ringwoodite crystals up to 1000 μm in the largest dimension were grown at around 1400 °C with a temperature reduction of 110 °C during heating for 12 h. Bridgmanite crystals up to 600 μm in the largest dimension were grown at 1700 °C with a temperature reduction of 30 °C during heating for 12 h. A TOF single-crystal diffraction instrument has been successfully used for analyzing one of the hydrous wadsleyite crystals, which demonstrated that single crystals appropriate for their expected usage are created using the method proposed in the present study.

Redetermination of bis(acetylacetonato-κ2O,O′)(1,10-phenanthroline-κ2N,N′)manganese(II)

In the crystal structure of the title compound, [Mn(C5H7O2)2(C12H8N2)], the Mn2+ cation is coordinated by one bidentate 1,10-phenanthroline ligand and two acetyl­acetonate anions within a slightly distorted N2O4 octa­hedron. The asymmetric unit consists of one Mn2+ cation situated on a twofold rotation axis, one half of a 1,10-phenanthroline ligand and one acetyl­acetonate anion. In comparison with the previous determination based on visually estimated intensities recorded on precession photographs, the current redetermination with image-plate data reveals bond lengths and angles with much higher precision.

Single-crystal synthesis and structure refinement of Li 2MoO 3

Single crystals of Li 2MoO 3 were successfully synthesized by a flux method at 1473 K. The average crystal structure having the trigonal R3¯ m space group and the lattice parameters a=2.8736(11) Å and c=15.038(3) Å has been refined to the conventional values R=4.8% and wR=3.6% using 124 independent reflections. The site population refinement revealed the Mo-rich structural formula of Li 1.31Mo 0.69O 2 for the present single-crystal specimens. Superlattice spots and/or diffuse scatterings suggesting the Mo 3 cluster structure were observed in the single-crystal X-ray precession photographs.

Synthesis, Crystal Structure, and Magnetic Property of Delithiated LixMnO2 (x < 0.1) Single Crystals: A Novel Disordered Rocksalt‐Type Manganese Dioxide.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis, Crystal Structure, and Magnetic Property of Delithiated LixMnO2 (x < 0.1) Single Crystals: A Novel Disordered Rocksalt-Type Manganese Dioxide

Single crystals of the chemically and electrochemically delithiated LixMnO2 (x < 0.1) have been successfully synthesized from the parent orthorhombic LiMnO2 single crystals. A single-crystal X-ray diffraction study revealed that the average structure of LixMnO2 was the disordered rocksalt-type with the space group Fm3m, and the lattice parameter a = 4.095(3) A. Some additional spots indicating the superlattice structure and diffuse scattering could be observed in the X-ray precession photographs. The mechanism of the structural transformation from the parent orthorhombic LiMnO2 to the delithiated cubic LixMnO2 was well explained by the manganese ion migration accompanied with Li+ extraction. The magnetic properties of the chemically delithiated LixMnO2 are compared with those of the parent LiMnO2. The extracted Curie constant in LixMnO2 is consistent with the residual lithium content found analytically, as in the case of λ-MnO2.

Coexistence of Two Polytypic Groups in Cronstedtite From Lostwithiel, England

AbstractCronstedtite from Lostwithiel, Cornwall, England, in which two polytypic groups (A and C) are present within the same crystal, has been investigated using various techniques to reveal the distribution of the two groups and the relationship between polytypic structure and chemical composition. X-ray precession photographs from cleaved fragments of pyramidal crystals revealed the variable proportions of the two groups from the top to the base. Near the top, the crystal consists entirely of group C, with 1T as the dominant polytype. Near the base, both groups A and C are present. Back-scattered electron images from cross-sections parallel to the pyramidal axis showed mosaic contrast near the base, suggesting that two compositionally-different domains of several tens of microns in size are present, whereas the contrast was uniform near the top. Electron microprobe chemical analysis indicated the compositions (Fe2.312+Fe0.693+)(Si1.31Fe0.693+)O5(OH)4 and (Fe2.162+Fe0.843+)(Si1.16Fe0.843+)O5(OH)4. Electron back-scattered patterns (EBSPs) confirmed that the domain with Si-rich composition belongs to group C and that with Si-poor composition to group A. This is the first evidence that specific chemical compositions are related to the polytypic structures in cronstedtite. Transmission electron microscopy revealed that intergrowth of groups A and C at the monolayer level is also present as stacking disorder in both domains near the base, whereas such intergrowth was not observed in the region near the top.

Synthesis of a Si-clathrate compound, Sr 8Ga xSi 46− x, and its electrical resistivity measurements

Si-clathrate compounds, Sr 8Ga x Si 46− x ( x=11 and 12), were synthesized by two methods: Ar-arc melting and floating-zone melting. The Ar-arc melting of a mixture of SrSi 2, Ga, and Si resulted in multiphase samples including the Si-clathrate, Sr 8Ga 12Si 34. A single-phase Sr 8Ga 11Si 35 was synthesized by floating-zone melting. Powder X-ray-diffraction patterns and precession photographs indicate that Sr 8Ga 11Si 35 is a type-I clathrate with a lattice constant of a=10.4075(3) Å. Sr 8Ga 11Si 35 is a metal whose dominant carriers are electrons, and it does not show superconductivity down to 2 K.

KAMPFITE, A NEW BARIUM SILICATE CARBONATE MINERAL SPECIES FROM FRESNO COUNTY, CALIFORNIA

Kampfite, ideally Ba6[(Si,Al)O2]8(CO3)2Cl2(Cl,H2O)2, is a newly identified mineral species found in barium-silicate-rich deposits at Big Creek and Rush Creek, Fresno County, California. It forms irregular masses up to 10 mm in size enclosed in quartz-rich portions of the sanbornite-bearing rock. It is light blue-grey, with one perfect cleavage on {001}. Other physical properties are: brittle, translucent, nonfluorescent, vitreous luster, white streak, hardness 3, uneven fracture. Kampfite is uniaxial negative, ω 1.642(2), e 1.594(2), nonpleochroic. It is hexagonal, with unit-cell parameters refined from powder data: a 5.244(2), c 29.83(1) A, V 710.5(4) A3, and Z = 1. The strongest seven lines of the X-ray powder-diffraction pattern [ d in A( I )( hkl )] are: 14.67(100)(002), 3.883(100)(104), 3.357(50)(106), 2.988(60)(0010), 2.887(50)(108), 2.616(70)(110), and 1.969(50)(1110). Precession photographs show that possible space-groups are P 63/ mmc , P 62 c , P 63 mc , P 31 c and P 31 c . The empirical formula of kampfite (based on the average of three electron-microprobe analyses, normalized on 26 anions) is: (Ba5.83Na0.04Ca0.02)∑5.89[(Si5.18Al2.36)∑7.54O15.08](CO3)2Cl2[(H2O)Cl0.45]∑1.45. The calculated density is 3.51 g/cm3. All crystals studied contain inclusions or are multiple. Thus, it was not possible to unambiguously determine the correct space-group or precise details of the structure. However, the preliminary results show that the structure is based on double layers of tetrahedra, [ T 4O8]∞, consisting of six-membered rings, with three layers of Ba polyhedra connecting the layers of tetrahedra. Kampfite is part of the monteregianite-(Y) – wickenburgite series (Strunz classification) and is structurally and chemically similar to cymrite. The mineral name honors Anthony R. Kampf, Los Angeles County Museum of Natural History, for his many significant contributions to the study of new and rare minerals.

TRIVALENT IODINE IN THE CRYSTAL STRUCTURE OF SCHWARTZEMBERGITE, Pb2+5 I3+ O6 H2 Cl3

The crystal structure of schwartzembergite from the San Rafael mine, Sierra Gorda, Chile, tetragonal, a 3.977(1), c 12.566(4) A, I 4/ mmm , has been refined to an R index of 1.8% based on 103 unique observed ( I > 5σ I ) reflections. Schwartzembergite is optically biaxial, but long-exposure precession photographs show no evidence of non-tetragonal symmetry. The tetragonal structure consists of interleaved PbO and Cl sheets stacked along the four-fold axis. The Pb and I sites are both coordinated by four O atoms arranged in a square to one side of the cation, with Pb–O = 2.407(3) A and I–O = 2.15(1) A. The Pb and I sites are only 0.54(4) A apart, and hence cannot both be occupied at the local scale. The Pb site is also coordinated by four Cl atoms at a distance of 3.331(3) A and arranged on the opposite side of the site to the O atoms; this very asymmetric coordination is characteristic of Pb 2+ exhibiting stereoactive lone-pair behavior. Bond-valence summation around the I site gives a value of 2.92 vu (valence units), indicating the iodine to be trivalent (rather than pentavalent, as has been assumed in previous studies); this is the first recorded occurrence of trivalent I in a mineral. Single-crystal polarized infrared and 1 H MAS NMR spectroscopies indicate the presence of structural H. Chemical analysis by electron microprobe and H-line extraction (1.20 wt.% H 2 O) gave the formula Pb 2+ 5 I 3+ O 6 H 2 Cl 3 . Electron diffraction showed numerous superlattice reflections, suggesting a C - or I -centered orthorhombic supercell with a = 2 a s , b = 6 b s , c = c s ( i.e. , an 8 × 24 A supercell), where the subscript s denotes the (pseudo-) tetragonal subcell. The observed substructure and local bond-valence requirements indicate that the (I 3+ O 4 ) groups cannot polymerize, and that I 3+ must occur on both sides of the oxygen layer in each (Pb,I)O sheet. These constraints result in five possible motifs for the superstructure; one of these sheets somewhat resembles the ordered sheet in nadorite, Pb 2+ Sb 3+ O 2 Cl, suggesting that this may be the pattern of order in schwartzembergite.

Preparation and crystal structure of quaternary chromium sulfide halide CrSBr 0.67Cl 0.33

Quaternary CrSBr 0.67Cl 0.33 was obtained as black needles by heating chromium powder with a mixture of S 2Br 2 and S 2Cl 2 at 1273 K. It was found from X-ray precession photographs and an X-ray diffraction powder structure determination to be isostructural with CrSBr crystallizing in the FeOCl structure type (space group Pmmn, a = 476.73(4), b = 346.65(3), and c = 779.25(8) pm; R exp = 9.7%). The reason of the partly opposite change of the Cr–X (X = halogen) and Cr–S distances on going from CrSBr to CrSBr 0.67Cl 0.33, compared with that expected for substitution of bromium ions by smaller chlorium ones, is discussed.

Crystallographic CourseWare

Crystallographic CourseWare is a set of computer animations and interactive exercises designed to assist undergraduate and introductory graduate students in their learning of crystallography. Topics discussed include crystal growth, plane- and space-group symmetry elements, unit cells and asymmetric units, reciprocal space, precession photographs, and an introduction to reading the International Tables for Crystallography .

Electrocrystallization of PrO2 and TbO2− from alkali hydroxide melts and characterization of the fluorite-related TbO2−

Single crystals of PrO2 and of the oxygen deficient fluorite related phase TbO2−x have been obtained by anodic electrocrystallization from alkaline hydroxide melts containing PrCl3 and TbCl3, respectively. Magnetic measurements, X-ray diffraction data and TEM investigations confirm the identity of the products. PrO2 crystallizes in a fluorite type of structure with a=5.3945(3) Å and shows paramagnetic behaviour with a magnetic moment as expected for Pr4+ (μeff=2.49μB, Θ=−109 K, TN=10 K). According to precession photographs and an examination with an area sensitive X-ray detector, TbO2−x exhibits a superstructure of fluorite with a pseudocubic subcell with af=5.2810(1) Å. This lattice constant is intermediate between those of TbO2 and Tb2O3 (C-type), the same is true for its paramagnetic behaviour (μeff=8.58μB, Θ=−22 K, TN=5 K). The supercell was found to be hexagonal with a=25.836(1) Å and c=36.672(2) Å, the symmetry of the intensity distribution being monoclinic. Electron diffraction revealed a cubic cell with a=10.6 Å, space group Ia-3, indicating reduction of the material in the electron beam.

Topotaxial replacement of chlorapatite by hydroxyapatite during hydrothermal ion exchange

Exchange of Cl⁻ by OH⁻ in synthesized chlorapatite single crystals was investigated under hydrothermal conditions. Hydrothermal treatments were performed at various temperatures from 200 to 500 °C, for intervals between 3 and 96 h in KOH or NaOH solutions. Ion exchange of Cl⁻ in the chlorapatite crystals was completed at low temperature (500 °C) for a short time (12 h) in 6.25 M KOH solution, and resulted in the formation of hydroxyapatite. The rate of ion exchange was accelerated by increasing the reaction temperature and/or concentration of the alkaline solutions. That the converted crystals were single crystals of hydroxyapatite was confirmed by X-ray precession photographs. The hydroxyapatite single crystals that formed from the chlorapatite single crystals by the topotaxial ion exchange under alkaline hydrothermal conditions had a characteristic texture, exhibiting channels on the surfaces and tunnels inside, both along the c axis of the crystals. A dissolution and precipitation process is proposed for the ion-exchange reaction conducted under hydrothermal conditions.

Structure and physical properties of the quaternary Remeika-phase compoundYb5Pt6In16Bi2

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The crystal chemistry of sogdianite, a milarite-group mineral

The crystal structure of sogdianite, hexagonal, a = 10.053(1), c = 14.211(2)Aa, V = 1243.8(4)Aa 3 , space group = P6/mcc, Z = 2, has been refined to an R index of 2.0% using 607 observed (F 0 > 5F) reflections collected with an automated four-circle diffractometer using MoKalpha X-radiation. Site-scattering refinement and electron-microprobe analysis indicate the composition Zr (sub 0.76) Ti (super 4+) (sub 0.38) Fe (super 3+) (sub 0.73) Al (sub 0.13) ) (sub Sigma = 2) ( (sub 1.15) Na (sub 0.85) ) (sub Sigma = 2) K[Li 3 Si 12 O 30 ]. The T2 tetrahedron is completely occupied by Li, and all Al occurs at the octahedrally coordinated A site. The A-O bond length is compatible with all Fe being in the trivalent state. There is no significant positional disorder of the A-group cations, in accord with the absence of H 2 O in sogdianite. Single-crystal X-ray precession photographs of sogdianite show the presence of diffractions that are incommensurate with the sogdianite diffraction pattern. The relative intensity of the incommensurate diffractions increases with the degree of apparent alteration of sogdianite (clear-->turbid-->murky), suggesting that sogdianite is altering to, or possible exsolving, a second phase, probably zektzerite.

Crystallographic CourseWare

Crystallographic CourseWareis a set of computer animations and interactive exercises designed to assist undergraduate and introductory graduate students in their learning of crystallography. Topics discussed include crystal growth, plane- and space-group symmetry elements, unit cells and asymmetric units, reciprocal space, precession photographs, and an introduction to reading theInternational Tables for Crystallography.

LAYER– a computer program for the graphic display of intensity data as simulated precession photographs

LAYERis a 32-bit Microsoft Windows-based program that reads intensity data inSHELXtype 4 format and displays any level of the reciprocal-lattice net. The program is primarily intended for instructive purposes, but may also prove useful as a visual complement to statistically based numeric analysis of diffraction data for space-group determination.

Tcl/Tk-based programs. III.CRITXPL: graphical analysis of theX-PLORrefinement log files

# 1999 International Union of Crystallography Journal of Applied Crystallography Printed in Great Britain ± all rights reserved ISSN 0021-8898 # 1999 de®ned by the data-processing programs. In the calculated positions, it displays the logarithm of the diffraction intensity or amplitude of each reciprocal-lattice point with radius and degree of darkness according to the input values. Any planes of the reciprocal lattice can be displayed. When the index and amplitude or intensities (h, k, l, F or I ) of all the re ections are read, the program produces pictures very similar to real precession photographs.