Refined Unit Cell Research Articles

Synthesis, Characterization, and Structure Solution of CIT-5, a New, High-Silica, Extra-Large-Pore Molecular Sieve

The synthesis, structure solution, and characterization of the high-silica molecular sieve CIT-5 (California Institute of Technology Number 5) is described. CIT-5 is synthesized at hydrothermal conditions in the presence of N(16)-methylsparteinium and preferrably lithium cations. The structural solution of CIT-5 shows that it contains one-dimensional pores circumscribed by 14 tetrahedral atoms (14 MR). Rietveld refinement of the synchrotron X-ray powder data gives a symmetry and space group assignment for the structure of Pmn2_1 (no. 31) with refined unit cell parameters of a = 13.6738(8) A, b = 5.0216(3) A, and c = 25.4883(7) A (V = 1750.1 A^3). Electron diffraction and transmission electron microscopy confirm the space group and the topology of the structure viewed along the [010] direction. Solid-state ^(29)Si NMR spectroscopy results are consistent with the space group assignment. The thermal/hydrothermal stability of CIT-5 compares well to that of other large- and extra-large-pore, high-silica molecular sieves. The acid form of CIT-5 is able to perform hydrocarbon reactions such as cracking and alkylation and shows behaviors that are different from other zeolites.

Reversed determination of the reaction; phlogopite+quartz = enstatite+potassium feldspar+H2O in the ranges 750-875 degrees C and 2-12 kbar at low H2O activity with concentrated KCl solutions

The reaction of phlogopite plus quartz to enstatite, potassium feldspar, and aqueous fluid in the system KMASH-KCl was reversed at 2-12 kbar and 750-875 degrees C and at low H 2 O activities by reversal of the H 2 O content of concentrated KCl solutions equilibrated with product and reactant assemblages. Synthetic 1M phlogopite [KMg 3 AlSi 3 O 10 (OH) 2 ] and enstatite (MgSiO 3 ) maintained end-member stoichiometry throughout, and the potassium feldspar (KAlSi 3 O 8 ) was a high sanidine, based on unit-cell refinements. The broad P-T-XH 2 O and narrow reversal ranges of this investigation were possible because of the low and well-defined H 2 O activity, yet powerful fluxing action, of concentrated KCl solutions. Solubility experiments on quartz and potassium feldspar in our P-T-XH 2 O range showed that fluid-phase solution of silicate constituents was too small to have affected the H 2 O activity in the experiments. The new determinations are more definitive than previous work done at very low pressures with pure H 2 O or in CO 2 -H 2 O mixtures. They establish the standard free energy of the reaction in the experimental range with an uncertainty of about 1 kJ and indicate that the synthetic phlogopite has maximal (Al-Si) disorder under our experimental conditions. The standard enthalpy of reaction at 298 K is 106.54+ or -2.0 kJ (2sigma ) based on our reversals, a value 6 kJ less positive than that currently used by many workers in calculations of biotite stability and H 2 O activity in the petrogenesis of high-grade metamorphic rocks. The lower thermal stability that we find for phlogopite requires revision in estimates of H 2 O activity of granulite facies metamorphism: typical values for the natural assemblage orthopyroxene-biotite-garnet-potassium feldspar-plagioclase-quartz at deep-crustal metamorphic conditions (750-850 degrees C, 5-10 kbar) are alpha H2O = 0.4-0.6 compared with values of 0.15-0.30 which would have been estimated with previously available data on phlogopite stability. An important consequence of the expanded H 2 O activity range of granulites is that alkali chloride solutions of only moderate concentration [XH 2 O = 0.5-0.7], which are the values observed in actual fluid inclusions in many kinds of igneous and metamorphic rocks, are a feasible alternative to the vapor-absent conditions considered necessary by many workers based on previous low estimates of H 2 O. Participation of concentrated brines in deep-crust/upper mantle metamorphic processes enables alkali metasomatism and other kinds of chemical transport in an aqueous fluid without large-scale melting of the crust.

X-ray powder diffraction analysis of a nonlinear optical material 1-benzoyl-3-(4-benzyl)thiourea [N-benzoyl-N′-(4-benzyl)thiourea

A nonlinear optical material, 1-benzoyl-3-(4-benzyl)thiourea (C15H14N2OS), has been characterized by X-ray powder diffraction. Experimental values of 2θ corrected for systematic errors, relative peak intensities, values of d, and the Miller indices of 82 observed reflections with 2θ up to 80° are reported. The powder diffraction data have been evaluated, and the figures-of-merit are reported. The least-squares refined unit cell parameters are a=22.0243(6)Å, b=10.9795(7)Å, c=13.0322(8)Å, β=116.88(2)°, V=2810.8(9)Å3, Z=8, Dx=1.278 g/cm3, space group Pn.

New ternary compounds in the BaO:Fe2O3:TiO2 system: Ba2Fe2Ti4O13 (“2:1:4”), Ba3Fe10TiO20 (“3:5:1”), and Ba4Fe2Ti10O27 (“4:1:10”)

X-ray powder diffraction data and refined unit cell parameters for three compounds found during experimental determination of the BaO:Fe2O3:TiO2 phase diagram are reported here. All three phases crystallize in space group C2/m (No. 12). Ba2Fe2Ti4O13 (“2:1:4”) is isostructural with K2Ti6O13 and Ba2ZnTi5O13: a=15.1939(9), b=3.8912(3), c=9.1244(5) Å, β=98.456(5)°; Z=2, ρcalc=4.890 g/cc. Ba3Fe10TiO20 (“3:5:1”) is structurally analogous to its aluminum congener Ba3Al10TiO20: a=15.336(1), b=11.7986(9), c=5.1700(4) Å, β=91.220(6)° (I2/m setting); Z=2, ρcalc=4.750 g/cc. Ba4Fe2Ti10O27 (“4:1:10”) is also isostructural with its aluminum analog Ba4Al2Ti10O27: a=19.799(1), b=11.4324(6), c=9.8936(6) Å, β=109.146(4)° (C2/m); Z=4, ρcalc=4.934 g/cc. The 2:1:4 and 3:5:1 compounds adopt open-framework type structures while the 4:1:10 phase exhibits an eight-layer close-packed arrangement.

Indexing of incommensurate satellite reflections in X-ray powder diffraction pattern of (Bi, Pb)2Sr2Ca2Cu3Ox (2223) phase

X-ray powder diffraction data and refined unit cell parameters for the (Bi, Pb)2Sr2Ca2Cu3Ox (2223) superconducting phase, indexed using incommensurate modulation principles, are reported. Comparison of the results obtained with one- and two-component modulation wave vectors showed that the two-component modulation wave vector is superior for indexing the satellite reflections. A two-component wave vector indexing result seems likely when only the powder diffraction data are considered.

Powder diffraction data and Rietveld refinement of metastable t-ZrO2 at low temperature

Indexed X-ray powder diffraction data are reported for the low temperature tetragonal ZrO2 obtained by crystallization of zirconia gel. The structure was refined by the Rietveld technique on the basis of space group P42/nmc. Refined unit cell dimensions are a = 3.5984(5) Å, c = 5.152(1) Å, V = 66.71 Å3, Dx=6.135 g/cm3, F18=62 (0.012, 24), RP=8.99, Rwp=11.48, RB=3.13.

A series of “chemically twinned rutile” oxides, SrM2n+1O4n+5 (M=Ti, Nb; n=3→9)

X-ray powder diffraction data and refined unit cell parameters for SrTi3Nb4O17, SrTi5Nb4O21, SrTi7Nb4O25, SrTi9Nb4O29, SrTi11Nb4O33, SrTi13Nb4O37, and SrTi15Nb4O41 are reported here. The powder patterns for these oxides suggest that they form a homologous series SrM2n+1O4n+5 (M=Ti, Nb; n=3→9), which is isostructural with the orthorhombic “chemically twinned rutile” series found previously in the K2O-TiO2-Ta2O5 and BaO-TiO2-Nb2O5 systems. The structures are built of corner-sharing slabs of the rutile structure; successive members are generated by adding 2TiO2 to the slab thickness of the previous member. The series crystallizes in space group Cmcm (No. 63), with members exhibiting similar a-, b-dimensions (∼6.6, ∼8.9 Å; respectively), and c-dimensions that linearly increase (by ∼4.4 Å per member) from 20.8 Å for n=3 to 47.1 Å for n=9.

An XRD and Electron Diffraction Study of Cristobalite-Related Phases in the NaAlO2–NaAlSiO4System

A detailed study of the sodium aluminate–carnegieite system (Na2−xAl2−xSixO4, 0≤x≤1) at temperatures between 800 and 1300°C has revealed five previously unreported phases. All of the new phases can be described as modulated variants of an underlyingβ-cristobalite parent structure. Atx≈0.05 theγ-NaAlO2-type structure (P41212,a=1/2ap,c=cp) (p=parent) is stabilized to room-temperature; atx≈0.2–0.45 an orthorhombic (Pbca,a=2ap,b=2bp,c=1/2cp) KGaO2-type structure is obtained, except atx≈0.35 where a new tetragonal (P41212,a=2ap,c=cp) phase is observed; atx≈0.5–0.6 a new cubic (P213,a=2ap) phase is obtained; atx≈0.7–0.9 a new orthorhombic (Pc21b,a=2ap,b=2bp,c=2cp) phase is obtained. XRD and electron diffraction data, refined unit cell dimensions, and the phase relationships at 1300°C are presented. The proposed space group symmetries are based on observed extinction conditions and constraints provided by a modulated structure description of the new phases. The materials are prepared by gel synthesis followed by solid state reaction in air.

Unit cell refinement from powder diffraction data: the use of regression diagnostics

AbstractWe discuss the use of regression diagnostics combined with nonlinear least-squares to refine cell parameters from powder diffraction data, presenting a method which minimizes residuals in the experimentally-determined quantity (usually 2θhkl or energy, Ehkl). Regression diagnostics, particularly deletion diagnostics, are invaluable in detection of outliers and influential data which could be deleterious to the regressed results. The usual practice of simple inspection of calculated residuals alone often fails to detect the seriously deleterious outliers in a dataset, because bare residuals provide no information on the leverage (sensitivity) of the datum concerned. The regression diagnostics which predict the change expected in each cell constant upon deletion of each observation (hkl reflection) are particularly valuable in assessing the sensitivity of the calculated results to individual reflections. A new computer program, implementing nonlinear regression methods and providing the diagnostic output, is described.

The Natural Occurrence of Eta-Alumina (η-Al2O3) in Bauxite

AbstractApproximately 20 wt.% of the bauxite from Andoom in northern Queensland, Australia is composed of material that cannot be accounted for by identifiable well-crystallized phases. This poorly-diffracting material (PDM), found within the core of bauxitic pisoliths, has similar characteristics to that of eta-alumina (η-Al2O3); a cubic form of alumina. A differential XRD pattern of the PDM displayed a series of broad diffraction maxima attributed to eta-alumina with a mean crystal size of 9 nm. Unit cell refinement, on the basis of a cubic cell, gave a lattice parameter of a = 7.98 Å for Andoom eta-alumina. TEM and selected-area electron diffraction revealed the PDM to be composed of minute (10 nm wide), randomly oriented crystals of eta-alumina in close association with Al-hematite. Chemical analysis using a nanoprobe showed Andoom eta-alumina to be almost pure alumina with <2 M% Fe, <1 M% Si and <1 M% Ti. The closely associated Al-hematite may contain as much as 22 M% Al, however a value closer to the theoretical limit of 17 M% is more likely. A broad absorption band at 3450 cm−1 and 1630 cm−1 in the infra-red spectrum of the PDM indicates the presence of a substantial quantity of H2O, strongly adsorbed onto the surface of the crystals. This is presumably due to η-Al2O3's large surface area of approximately 2200 m2/g. The natural occurrence of η-Al2O3 in bauxite may be the result of low H2O activities within the micro-environment of pores at the time of crystallization. The epigenetic replacement of kaolinite with η-Al2O3 and Al-hematite is put forward as an explanation for the formation of bauxitic pisoliths at Andoom.

Solid-State Synthesis, X-Ray Powder Diffraction, and IR Data of Na 2GdOPO 4

Na 2GdOPO 4, sodium gadolinium oxyphosphate, was prepared by the solid state reaction of Gd 2O 3 + Na 4P 2O 7 and its X-ray powder diffraction data was studied. The compound prepared at 1200°C showed the presence of two polymorphs which are orthorhombic and pseudoorthorohombic (monoclinic). The refined unit cell parameters were found to be a = 13.074(6), b = 10.637(5), c = 6.469(3) Å for the orthorhombic form. The X-ray powder data and the cell parameters were quite similar to that of RbTiOPO 4. The IR spectra of the compound is identical to that of M 1 TiOPO 4 ( M 1 = K, Rb, Tl) except for three Ti-O vibrations.

Powder diffraction data and Rietveid refinement of the compound Ba2Cl2Cu3O4

Indexed X-ray powder diffraction data are reported for the semiconducting compound Ba2Cl2Cu3O4. The structure was refined by the Rietveid technique on the basis of the space group I4/mmm. Refined unit cell dimensions area= 5.5156(1) Å,c= 13.8221(3) Å,V= 420.49 Å3Dx= 4.74 g/cm3,F30= 129(0.0075,30),M20= 121,Rp= 6.58,Rwp= 8.66, andRB= 4.49.

H in rutile-type compounds; II, Crystal chemistry of Al substitution in H-bearing stishovite

Other| June 01, 1995 H in rutile-type compounds: II. Crystal chemistry of Al substitution in H-bearing stishovite Joseph R. Smyth; Joseph R. Smyth University of Colorado, Department of Geological Sciences, Boulder, CO, United States Search for other works by this author on: GSW Google Scholar R. Jeffrey Swope; R. Jeffrey Swope Search for other works by this author on: GSW Google Scholar Alison R. Pawley Alison R. Pawley Search for other works by this author on: GSW Google Scholar American Mineralogist (1995) 80 (5-6): 454–456. https://doi.org/10.2138/am-1995-5-605 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Joseph R. Smyth, R. Jeffrey Swope, Alison R. Pawley; H in rutile-type compounds: II. Crystal chemistry of Al substitution in H-bearing stishovite. American Mineralogist 1995;; 80 (5-6): 454–456. doi: https://doi.org/10.2138/am-1995-5-605 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract The crystal structures of a synthetic H-bearing aluminous stishovite, containing approximately 1.6 wt% Al2O3, and a pure-silica stishovite have been refined from threedimensional, single-crystal X-ray diffraction data. The space group of both is P42/mnm, and the unit cell parameters of the aluminous crystal are a = 4.1839(8) and c = 2.6684(6) Å, which are slightly larger than those of pure silica [a = 4.1773(4) and c = 2.6652(2) Å], The Al-bearing octahedron is slightly larger and more regular than that of pure-silica stishovite. Unit cell and atom position refinement are consistent with 1.6% substitution of Al for Si. The observation of 1.9% Al substitution for [6]Si, even without clear charge balance, is evidence that this substitution may be significant in many lower mantle silicate phases. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Structure refinement, electron microscopy, and solid-state magic angle spinning nuclear magnetic resonance characterization of AlPO 4-52: An aluminophosphate with a large cage

Synchrotron powder X-ray diffraction (PXRD) data for calcined AlPO 4-52 were refined in space group P 3 1c using the Rietveld method. The previously proposed topology (AFT), an ABC six-ring structure type with an AABBCCAACCBB stacking sequence, was confirmed. The refined unit cell dimensions are a = b = 13.715 (1) Å and c = 29.676 (3) Å. Possible causes for peak broadening in the synchrotron PXRD profile were examined. A series of PXRD patterns obtained at various temperatures indicated that the calcined sample used for synchrotron PXRD was partially rehydrated. Electron diffraction patterns showed particle texture effects but no evidence for faulting or disorder. Individual crystallites of AlPO 4-52 are roughly equidimensional hexagonal prisms. Preferred orientation of the crystallites was not evident. Solid-state magic angle spinning nuclear magnetic resonance (MAS n.m.r.) spectra of calcined never-rehydrated AlPO 4-52 showed that all aluminum and phosphorus atoms were tetrahedrally coordinated. However, MAS n.m.r. spectra of a calcined rehydrated sample showed a 1:2 ratio of tetrahedral to octahedral aluminum atoms due to extraframework water coordination. The 31P MAS n.m.r. spectra are consistent with phosphorus atoms located exclusively in double six-rings.

X-ray powder diffraction pattern for lactitol and lactitol monohydrate

Diffraction patterns were recorded, and unit cell dimensions refined by the least-squares method, for lactitol and lactitol monohydrate. Refined unit cell parameters for lactitol are: a =7.622(1) Å, b = 10.764(2) Å, c = 9.375(1) Å, β= 108.25(1)° in space group P21, and those for lactitol monohydrate a =7.844(1) Å, b = 12.673(2) Å, c = 15.942(2) Å in space group P212121.

Annite stability revised. 1. Hydrogen-sensor data for the reaction annite = sanidine + magnetite + H2

In P - T - logfO2 space, the stability of annite (ideally KFe 3 2+ (OH)2AlSi3O10) at high fO2 (low fH2) is limited by the reaction: annite = sanidine + magnetite + H2. Using the hydrogen-sensor technique, the equilibrium fH2 of this reaction was measured between 500 and 800° C at 2.8 kbar in 50° C intervals. Microbrobe analyses of the reacted annite+sanidine+magnetite mixtures show that tetrahedral positions of annite have a lower Si/Al ratio than the ideal value of 3/1. Silicon decreases from ∼2.9 per formula unit at low temperatures to ∼2.76 at high temperatures. As determined by Mossbauer spectroscopy in three experimental runs, the Fe3+ content of annite in the equilibrium assemblage is 11%±3. A least squares fit to the hydrogensensor data gives ΔH R 0 = 50.269 ± 3.987 kJ and ΔS R 0 = 83.01 ± 4.35 J/K for equilibrium (1). The hydrogene-sensor data are consistent with temperature half brackets determined in the classical way along the nickel-nickel oxide (NNO) and quartz-fayalite-magnetite (QFM) buffers with a mixture of annite+sanidine+magnetite for control. Compared to published oxygen buffer reversals, agreement is only found at high temperature and possible reasons for that discrepancy are discussed. The resulting slope of equilibrium (1) in logfO2 − T dimensions is considerably steeper than previously determined and between 400 and 800°C only intersects with the QFM buffer curve. Based on the hydrogen-sensor data and on the thermodynamic dataset of Berman (1988, and TWEEQ data base) for sanidine, magnetite and H2, the deduced standard-state properties of annite are: H f 0 =-5127.376±5.279 kJ and S 0=422.84±5.29 J/(mol K). From the recently published unit cell refinements of annites and their Fe3+ contents, determined by Mossbauer spectroscopy (Redhammer et al. 1993), the molar volume of pure annite was constrained as 15.568±0.030 J/bar. A revised stability field for annite is presented, calculated between 400 and 800°C.

X-ray powder diffraction data for five lanthanoid chromates [Ln2(CrO4)3(H2O)5]·2H2O (Ln=La,Pr,Nd,Sm,Eu)

X-ray powder diffraction data are reported for a series of isomorphous compounds of [Ln2(CrO4)3(H2O)5]·2H2O, where Ln=La, Pr, Nd, Sm, or Eu. The compounds crystallize in monoclinic space group P21/c (No: 14) with Z=4. Refined unit cell parameters and indexed powder diffraction patterns are given.

X-ray powder data for synthetic dolerophanite, copper(II) oxysulphate [Cu2O(SO4)

Bragg–Brentano X-ray powder diffractometry data and refined unit cell parameters are reported for a synthetic sample of dolerophanite, copper (II) oxysulphate [Cu2O(SO4)], prepared by heating AR copper (II) sulphate anhydrate in a muffle furnace at 725 °C. The data are compared with (i) two Debye–Scherrer patterns published by Mrose [Am. Mineral. 6, 146–153 (1961)]—for a synthetic sample and for a natural dolerophanite, the latter being pattern 13–189 in the ICDD Powder Diffraction File and (ii) a Debye–Scherrer pattern for a synthetic dolerophanite described by Borchardt and Daniels [J. Phys. Chem. 61, 917–921 (1957)]. A calculated pattern is also presented for the crystal structure of dolerophanite described by Effenberger [Monatschefte fur Chemie. 116, 927–931 (1985)]. The measured and calculated patterns reported here show reasonable internal consistency for both line positions and intensity data. While the agreement between these results and the data sets of Mrose is sound in terms of line positions, there is substantial disagreement overall between the intensity values given by the authors and those of Mrose. There is closer agreement between the intensities from the current study and those of Borchardt and Daniels.

X-ray powder diffraction data for cubic Sb3Nb3O13

An Sb3Nb3O13 [Sb(III)2Sb(v)Nb(v)3O13] phase having a defect pyrochlore structure has been prepared by heating a sol–gel derived powder in oxygen. X-ray powder diffraction results indicate that Sb3Nb3O13 has a face-centered cubic structure, S.G. Fd3m(227), with a refined unit cell parameter a =10.4965(1) Å, calculated density Dx=4.893, four molecules per unit cell (Z), and a calculated figure of merit SS/FOM F30=92.4(0.009,38).

POLISH: computer program for improving the accuracy of structure-factor magnitudes obtained from powder data

A computer program, POLISH, is presented that improves the accuracy of the structure-factor magnitudes obtained from powder data. This offers a greater likelihood of success for structure determination by direct methods or Patterson techniques. Generally, the program will be used in conjunction with a unit-cell refinement program, but it may also be used independently. Accurate values of the unit-cell and peak-shape parameters are required, which may be conveniently obtained from the unit-cell-refinement program. The program is tested by application to NDNO (V).