Four-circle Diffractometer Research Articles

ChemInform Abstract: Structure of Prudomestin.

3,5,7-Trihydroxy-8-methoxy-2-(4-methoxyphenyl)-4H1-benzopyran-4-one, C17H1407, M r = 330.3, triclinic, P1, a = 6.579 (5), b = 8.441 (7), c = 13.893 (14) A, a = 101.92 (9), fl = 103.38 (6), y = 97.44 (6) °, V = 721 A. 3, Z = 2, Dx = 1.52 g cm -3, Mo Ka radiation, A = 0.71069 A, /z = 1.2 cm-1, F(000) = 344, T = 200 K, R = 0.076 for 1534 unique observed [1/o-(/)_>2.0] reflections. The definitive structure of prudomestin is established by this investigation. The molecule is essentially planar with the methyl groups projecting above and below the plane. The major intermolecular force within a layer of molecules in the solid state results from hydrogen bonding. Introduction. Prunus domestica Linn. is the tree of the well-known fruit plum and grows ideally in the western temperate Himalayas and is cultivated for its fruit in India. Its fruits are used as a mild laxative and demulcent and, in combination with other drugs, they are used in leucorrhoea, irregular menstruation and debility following miscarriage (Chopra, Nayar & Chopra, 1956). The prudomestin used in this study 0108-2701/92/061090-03506.00 was extracted from the wood of Prunus domestica Linn. The objective of this investigation was to provide an unambiguous identification of the structure of prudomestin. Experimental. The prudomestin was isolated from the hot-water soluble portion of the benzene solubles of an alcoholic extract from the heartwood of Prunus domestica Linn. collected from Baramulla, Kashmir, India. The compound was recrystallized from chloroform-petrol and separated as yellow needles. Data were collected with a Siemens P3R3 fourcircle diffractometer in co-28 mode. The crystal was held at 200 K with an Oxford Cryosystems Cryostream Cooler (version 2.4); this temperature was chosen because the crystal diffracted rather poorly under ambient conditions. Maximum 20 was 50 ° with scan range _+ 0.7 ° (28) around the K a l Kot2 angles, scan speed 3-29 ° mini , depending on the intensity of the 2 s prescan; backgrounds were measured at each end of the scan for 0.25 of the scan time. hkl ranges were 0/7, 9/10, 15/15 (unique reflections only). Three standard reflections were © 1992 International Union of Crystallography V I R I N D E R S. P A R M A R et al. 1091 Table 1. Atomic coordinates (x 104) and equivalent isotropic thermal parameters (/~2 x 103) Ucq is defined as one third of the trace of the orthogonalized U U tensor.

ChemInform Abstract: Na2Hg3S4; a Thiomercurate with Layered Anions

Abstract Dark red crystals of Na 2 Hg 3 S 4 were obtained by reacting a stoichiometric mixture of Na 2 S and HgS at 870 K. Na 2 Hg 3 S 4 is orthorhombic, oP36 , space group Pbca with a=7.308(5) A , b=14.011(8) A , c=8.231(3) A and Z =4. The crystal structure was determined from four-circle diffractometer data and refined to a conventional R of 0.056 for 718 reflections with F 0 2 >3 σ ( F o 2 ) and 43 variables ( R w =0.065). Na 2 Hg 3 S 4 crystallizes with a new structure type whose outstanding feature is the formation of strongly corrugated anionic layers, α 2 - [Hg 3 S 4 ] 2− , running parallel to (010). These layers are based on a network of 16-membered rings formed by alternating mercury and sulphur atoms. Two thirds of the mercury atoms are in a trigonal planar co-ordination by sulphur (d Hg-S ≈ 2.49 A ) while the remaining atoms are linearly coordinated (d Hg-S =2.344 A ). The Na + ions are coordinated by five sulphur atoms in a distorted square pyramidal configuration. The structure of Na 2 Hg 3 S 4 can formally be derived from a distorted close-packed array of chalcogen atoms (stacking sequence, ( hc ) 2 ; stacking direction, [010]).

Spin State Transition Studied by Means of Optical Microscope

We have tested a new method which allows assigning the spin state of the spin crossover (SCO) crystal in-situ during the diffraction experiment. The method is based on the analysis of change of the colour of the SCO compounds. We have found that the off-line setup in transmission geometry is reliable in assigning the magnitude of high spin molecules fraction (γHS) and the character (one step, many steps, histeresis) of the SCO transition. Later on, this method has been used in the in-situ measurements directly on X-ray four-circle diffractometer.

CARBOBYSTRITE, Na8[Al6Si6O24](CO3){middle dot}4H2O, A NEW CANCRINITE-GROUP MINERAL SPECIES FROM THE KHIBINA ALKALINE MASSIF, KOLA PENINSULA, RUSSIA: DESCRIPTION AND CRYSTAL STRUCTURE

Carbobystrite, ideally Na 8 [Al 6 Si 6 O 24 ](CO 3 )·4H 2 O, trigonal, a 12.6678(5), c 10.3401(4) A, V 1437.0(2) A 3 , c:a = 0.8162, space group P 31 c , Z = 2, R = 0.0271 (for 4861 observed reflections collected with a four-circle X-ray diffractometer), is a new cancrinite-group mineral species from Mount Koashva, Khibina alkaline massif, Kola Peninsula, Russia. It formed in a pegmatitic environment. Associated minerals are: microcline, sodalite, megakalsilite, natrolite, pectolite, aegirine, natrite, nacaphite, vitusite-(Ce), fluorcaphite, belovite-(Ce), umbite, lemmleinite-K, lomonosovite, lovozerite, phlogopite, sphalerite and galena. The mineral was found in only one hand specimen of pegmatite as a corroded irregularly shaped grain about 3 mm across, intergrown with sodalite, megakalsilite and natrite. It is transparent, colorless with a white streak, a vitreous luster, and fluoresces pale yellow under ultraviolet light. Carbobystrite has a Mohs hardness of 6, is brittle with a conchoidal fracture, and has no cleavage. The calculated density is 2.366 g/cm 3 . Carbobystrite is uniaxial negative, non-pleochroic, ω 1.500(2), e 1.488 (2). The strongest six reflections in the X-ray powder-diffraction pattern [ d in A(I)( hkl )] are: 4.689(100)(012), 3.249(100)(132, 122), 6.378(80) (120), 2.661(80)(041, 123, 133), 3.867(70)(131, 121), and 3.664(70)(030). An electron-microprobe analysis gives Na 2 O 22.66, K 2 O 1.75, SiO 2 35.74, Al 2 O 3 30.42, CO 2 4.37, H 2 O 6.26, sum 101.20 wt.%, with CO 2 and H 2 O calculated from structural data. The empirical formula (based on O = 30.5 atoms per formula unit) is (Na 7.40 K 0.38 ) ∑7.78 (Al 6.04 Si 6.02 ) ∑12.06 O 24 (CO 3 )·3.5H 2 O; the simplified formula is Na 8 [Al 6 Si 6 O 24 ](CO 3 )·4H 2 O. The name carbobystrite denotes the compositional relation between the new mineral and bystrite, (Na,K) 7 Ca[Al 6 Si 6 O 24 ](S) 1.5 ·H 2 O; they are related by the substitution Na + + (CO 3 ) 2− + 2.5H 2 O → Ca 2+ + (S 2− ) 1.5 . The framework of Si,Al–O tetrahedra can be described as an ABAC stacking sequence. In the crystal structure, there are two LOSOD cages, and two e (cancrinite) cages per unit cell, giving a maximum of two (CO 3 ) groups and six H 2 O groups for the LOSOD-type cages and two H 2 O groups for the cancrinite cages, respectively. This is the first complex-sequence cancrinitegroup mineral with (CO 3 ) groups in cages larger than the cancrinite cages. Carbobystrite suggests a new series of carbonate equivalents of all known complex sequences in the cancrinite group.

GROATITE, Na Ca Mn2+2 (PO4) [PO3(OH)]2, A NEW MINERAL SPECIES OF THE ALLUAUDITE GROUP FROM THE TANCO PEGMATITE, BERNIC LAKE, MANITOBA, CANADA: DESCRIPTION AND CRYSTAL STRUCTURE

Groatite, ideally Na Ca Mn 2+ 2 (PO 4 ) [PO 3 (OH)] 2 , is a new mineral species from the Tanco pegmatite at Bernic Lake, Manitoba, Canada. It was found in a phosphate–carbonate mass in a spodumene-rich boulder. Groatite occurs sparingly as slightly divergent sprays of acicular crystals, embedded stellate sprays and as a tabular mass of densely intergrown acicular crystals. Groatite is closely associated with whitlockite, crandallite, an unidentified Na–Al phosphate and quartz; fairfieldite and manganese-rich overite are among the less closely associated phosphates; this assemblage may be secondary, following apparent dissolution of lithiophosphate and possibly of primary lithiophilite. Groatite is translucent, colorless to pale yellow and pale orange with a white streak and vitreous luster; it does not fluoresce under ultraviolet light. The Mohs hardness is 3. Groatite is brittle with an uneven fracture, and has a calculated density of 3.213 g/cm 3 . It is biaxial positive with α 1.622, β 1.634, γ 1.663 (all ±0.001), and is nonpleochroic; 2 V (obs.) = 67(1), 2 V (calc.) = 66.5°. It is monoclinic, space group C 2/ c , a 12.5435(9), b 12.4324(9), c 6.7121(4) A, β 115.332(2)°, V 946.07(19) A 3 , Z = 4. The six strongest lines in the X-ray powder-diffraction pattern [ d in A(I)( hkl )] are as follows: 3.187(100)(112), 2.726(90)(402, 240), 6.204(80)(020), 2.788(80)(330), 5.653(70)(200), and 2.580(70)(132, 420). Chemical analysis by electron microprobe gave P 2 O 5 46.66, FeO 0.49, MnO 29.31, CaO 12.51, Na 2 O 6.87, H 2 O (calc.) 3.93, sum 99.77 wt.%, where the H 2 O content was determined by crystal-structure refinement as OH = 2.0 apfu . The resulting empirical formula, on the basis of 10 O atoms and 2 (OH) groups pfu , is Na 1.02 Ca 1.02 (Mn 1.90 Fe 2+ 0.03 ) ∑ 1.93 P 3.02 O 10 (OH) 2 . The crystal structure of groatite was refined to an R index of 2.7% based on 831 unique reflections collected on a four-circle diffractometer with Mo K α X-radiation and a 4K CCD detector. There are two tetrahedrally coordinated T -sites occupied by P. There are two octahedra, M (1) and M (2), and an eight-coordinated A (2) site which are occupied by Ca, Mn and Na, respectively. The observed site-scattering, mean bond-lengths and bond-valence sums at these sites are in agreement with complete chemical order of Ca at M (1), Mn 2+ at M (2) and Na at A (2). A (PO 4 ) group is centered at the T (1) site and a PO 3 (OH) group at T (2). The H atom is located near the O(4) anion and provides a strong hydrogen bond to the O(2) anion. Groatite is isostructural with the acid arsenate mineral o’danielite and is a member of the alluaudite group; it is the first alluaudite-group mineral with an acid phosphate group. The new mineral is named in honor of Lee A. Groat, Professor of Mineralogy at the University of British Columbia in Vancouver. The species and the name groatite were approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA 2008–054).

Re-evaluation of formulae for X-ray stress analysis in polycrystalline specimens with fibre texture: experimental confirmation

Line splitting or line broadening of an X-ray Bragg reflection owing to a three-dimensional or biaxial load on a cubic polycrystalline specimen with 〈111〉 fibre texture has been predicted by Yokoyama & Harada [J. Appl. Cryst.(2009),42, 185–191] if the specimen is in the symmetry of the Laue classm{\overline 3}m. By using a TiN film specimen and a high-precision four-circle diffractometer with a laboratory X-ray source, it is shown that the profile of the 420 reflection is substantially different with and without biaxial load and also depends on the measurement direction, while the profile of the 222 reflection does not change. These results are quantitatively in agreement with the theoretical prediction, although the theory is based on the Reuss model of elasticity.

Discommensuration of Doped [Ca2CoO3] p CoO2

Single-crystal x-ray diffraction and high-resolution electron microscopy studies were carried out for Co-121 ([Ca2CoO3] p CoO2) and Sr-doped Co-121 grown in a KCl flux at 810°C. Typically, the samples were 2 mm × 2 mm × 0.02 mm in size. The single-crystal diffraction intensities were measured by the use of a four-circle diffractometer. Twinned super reflections, e.g., $$ 010\bar{1}/0\bar{2}04 $$ and $$ 020\bar{2}/0\bar{1}03 $$ were observed in the electron diffraction patterns. These super reflections were not observed in the end-member. Diffuse scattering was observed in the same reciprocal space by the single-crystal x-ray diffraction study. A discommensurate crystal model is proposed for the Sr-doped system.

Formalism for the determination of intermediate stress gradients using X-ray diffraction

A method is outlined that allows the determination of one-dimensional stress gradients at length scales greater than 0.2 mm. By using standard four-circle X-ray diffractometer equipment and simple aperture components, length resolutions down to 0.05 mm in one direction can be achieved through constant orientation of a narrow, line-shaped beam spot. Angle calculations are given for the adjustment of goniometer angles, and for the effective azimuth and tilt of the scattering vector for general angle settings in a four-circle goniometer. The latter is necessary for the computation of stresses from lattice strain measurements.

On the lattice parameters of silicon carbide

The thermal expansion coefficients of the hexagonal SiC polytypes 4H and 6H and with Al and N dopants have been determined for temperatures between 300 and 1770 K. Further, a set of the room temperature lattice parameters in dependence on doping with N, Al, and B has been obtained. Data for the thermal expansion were taken on a triple axis diffractometer for high energy x rays with a photon energy of 60 keV, which allows the use of large single crystals with a volume of at least 6×6×6 mm3 without the need to consider absorption. The room temperature measurements for samples with different dopants have been performed on a four-circle diffractometer. The thermal expansion coefficients along the a- and c-directions, α11 and α33, increase from 3×10−6 K−1 at 300 K to 6×10−6 K−1 at 1750 K. It is found that α11 and α33 are isotropic within 107 K−1. At high temperatures both coefficients for doped samples are ∼0.2×10−6 and 0.3×10−6 K−1 lower than for the undoped material.

THE CRYSTAL STRUCTURE OF BURGESSITE, Co2 (H2O)4 [AsO3(OH)]2 (H2O), AND ITS RELATION TO ERYTHRITE

The crystal structure of burgessite, ideally Co 2 (H 2 O) 4 [AsO 3 (OH)] 2 (H 2 O), a newly recognized supergene mineral from the Keeley mine, South Lorrain Township, Timiskaming District, Ontario, Canada, has been solved by direct methods and refined to an R index of 4.3% based on 494 observed reflections collected on a four-circle diffractometer with Mo K α X-radiation. Burgessite is monoclinic, space group P 2 1 / n , a 4.7058(12), b 9.299(3), c 12.738(4) A, β 98.933(8)°, V 550.6(5) A 3 , Z = 2, D meas = 2.93 g/cm 3 . The structure consists of one unique As site that is [4]-coordinated by O atoms and occupied by As 5+ with a As –O> distance of 1.694 A. There is one Co site occupied by Co and [6]-coordinated, with a Co –O> distance of 2.096 A. Bond-valence analysis of the final structure indicates three O atoms (O 2− ), one (OH) group and three (H 2 O) groups in the asymmetric unit; note that the (OH) group is bonded to the As 5+ cation, forming an acid arsenate group: AsO 3 (OH). The resulting ideal formula is Co 2 (H 2 O) 4 [As 5+ O 3 (OH)] 2 (H 2 O), where the (H 2 O) groups before the arsenate group are bonded to Co, and the (H 2 O) group following the arsenate group is held in the structure solely by hydrogen bonds. A prominent motif in the burgessite structure is the [Co 2 (H 2 O) 4 [As 5+ O 3 (OH)] 2 ] chain, which extends in the [100] direction and occurs at the vertices of an orthorhombic net. These chains are linked into a three-dimensional structure by hydrogen bonds that involve (OH) bonded to As 5+ , (H 2 O) bonded to Co, and (H 2 O) held in the structure solely by hydrogen bonds. The crystal structure of erythrite is based on [Co 2 (H 2 O) 4 (As 5+ O 4 ) 2 ] chains of the same bond-topology as that found in burgessite.

Synthesis, molecular structure, non-isothermal decomposition kinetics and adiabatic time to explosion of 3,3-dinitroazetidinium 3,5-dinitrosalicylate

Abstract The title compound 3,3-dinitroazetidinium (DNAZ) 3,5-dinitrosalicylate (3,5-DNSA) was prepared and the crystal structure has been determined by a four-circle X-ray diffractometer. The thermal behavior of the title compound was studied under a non-isothermal condition by DSC and TG/DTG techniques. The kinetic parameters were obtained from analysis of the TG curves by Kissinger method, Ozawa method, the differential method and the integral method. The kinetic model function in differential form and the value of E a and A of the decomposition reaction of the title compound are f(α)=4α3/4, 130.83 kJ mol−1 and 1013.80s−1, respectively. The critical temperature of thermal explosion of the title compound is 147.55 °C. The values of ΔS ≠, ΔH ≠ and ΔG ≠ of this reaction are −1.35 J mol−1 K−1, 122.42 and 122.97 kJ mol−1, respectively. The specific heat capacity of the title compound was determined with a continuous C p mode of mircocalorimeter. Using the relationship between C p and T and the thermal deco...

Helium cryostat synchrotron charge densities determined using a large CCD detector – the upgraded beamline D3 at DESY

A 165 mm Mar CCD detector has been fitted on a large Huber four-circle diffractometer together with a helium cryostat at beamline D3 at Hasylab, DESY in Hamburg. This setup allows fast collection of accurate, short-wavelength, very low temperature X-ray diffraction data for charge-density analysis. As a test example, diffraction data have been collected in 10 h on a hydrogen-bonded network system with 15 unique atoms, and the electron density was modelled with the multipole formalism in an X–N procedure using matching-temperature neutron diffraction data collected at Institut Laue Langevin, Grenoble in France.

Soft activation of the C-S bond: X-ray diffraction and spectroscopic study of the cluster Ru4(μ4-S)(μ,η3-C3H5)2(CO)12

The complex Ru4(μ4-S)(μ,η3-C3H5)2(CO)12 is prepared and examined by IR and NMR spectroscopy; its crystal structure is determined (an automatic Bruker-Nonius X8 Apex four-circle diffractometer equipped with a 2-D CCD-detector, 100 K, graphite-monochromated molybdenum source, λ = 0.71073 A). The crystal belongs to the orthorhombic crystal system with unit cell parameters a = 19.3781(9) A, b = 12.2898(7) A, c = 10.1726(4) A, V = 2422.6(2) A3, space group Pnma, Z = 4, composition C18H10O12Ru4S, dx = 2.343 g/cm3. The molecule of point symmetry C1 is situated on the mirror plane of the space group Pnma, two carbonyl groups at Ru2 and Ru3 atoms overlapping with the allylic ligand with a weight of 50% so that carbon atoms coincide. Thus, we have a racemic structure with two overlapping enantiomers of the molecule of Ru4(μ4-S)(μ,η3-C3H5)2(CO)12.

The crystal chemistry of the gedrite-group amphiboles. I. Crystal structure and site populations

AbstractThe crystal structures of twenty-five orthorhombic Fe-Mg-Mn amphiboles, a = 18.525 – 18.620, b = 17.806-18.034, c = 5.264-5.303 Å, V = 1737.6-1776.7, space group = Pnma, Z = 4, have been refined to R indices in the range 2.1–7.8% using 790–1804 unique observed reflections measured with Mo-Kα X-radiation on a Bruker P4 automated four-circle diffractometer equipped with a 1K CCD detector. The quality of the refinements is strongly a function of the [4]Al content of the crystals because of unmixing in the central part of the series due to the presence of a low-temperature solvus. The amphibole crystals were analysed by electron microprobe subsequent to collection of the X-ray intensity data and span the anthophyllite-gedrite series from 0.17–1.82 [4]Al a.p.f.u. Mössbauer spectroscopy shows that the amphiboles of this series commonly contain small but significant amounts of Fe3+ . The amount of [4]Al is linearly related to the grand <T-O> distance by the equation <T-O> = 1.6214 + 0.171 [4]Al, R = 0.980; the slope of this relation is not significantly different from that characteristic of a hard-sphere model. The <T-O> distances indicate the following site preference for [4]Al: T1B > T2B > T1A » T2A. The <M2-O> distances are compatible with all [6]Al and Fe3+ ordered at the M2 site. The grand <M1,2,3 '3 –O> distance is related to the mean radius of the constituent cations, <rM1,2,3>, by the equation ≪M1,2,3-O≫ = 1.4684 + 0.8553(7) <rM1,2,3>.

WHAT IS THE REASON FOR THE DOUBLED UNIT-CELL VOLUMES OF COPPER-LEAD-RICH PAVONITE HOMOLOGUES? THE CRYSTAL STRUCTURES OF CUPROMAKOVICKYITE AND MAKOVICKYITE

The crystal structure of cupromakovickyite, ideally Cu8Pb4Ag2Bi18S36, from the skarn deposit at Baiţa Bihor, in Romania, has been solved by direct methods and refined to an R 1 index of 5.36% for 2680 unique reflections measured with Mo K α radiation on a four-circle diffractometer equipped with a CCD detector. Cupromakovickyite has a monoclinic cell with a 13.405(8), b 4.016(3), c 29.949(19) A, β 99.989(16), V 1587.8(17) A3, space group C 2/ m and Z = 1. There are eight metal sites and twelve sulfur sites in each of the four asymmetric units. The thicker, galena-like layers are composed of parallel chains Bi4–Bi1–Bi1–Bi4 four octahedra long. In the thinner layers, the octahedra of Ag are replaced by two tetrahedrally coordinated Cu sites, whereas one of the paired square pyramids of Bi is replaced by Pb. The asymmetry of the thin layer is responsible for the doubling of the c parameter for cupromakovickyite with respect to makovickyite. To be able to compare them, the crystal structure of Cu-bearing makovickyite, Cu2.25Ag1.56 (Pb0.27Cd0.13)∑ 0.4Bi10.46S18, from a scheelite deposit at Felbertal, in Austria, has been refined to an R 1 index of 4.36% for 1320 unique reflections measured with the same equipment. Makovickyite has a monoclinic cell with a 13.239(3), b 4.0547(7), c 14.667(3) A, β 99.397(4), V 776.7(3) A3, space group C 2/ m and Z = 1. There are four metal sites and six sulfur sites in each of the four asymmetric units. The thicker, galena-like layers are composed of parallel chains Bi2–Bi1–Bi1–Bi2 four octahedra long. In the thinner layers, the octahedra of Ag are partially replaced by two tetrahedrally coordinated Cu sites.

Inversion of 4f-states in CeB6 thermally excited at 430 K

The 4f states of Ce in a typical Kondo crystal, CeB(6), are split into an excited state Gamma(7) and the ground state Gamma(8), with an excitation energy at 560 K. The electron-density distribution of the thermally excited state was measured at 430 K using a four-circle diffractometer equipped with a small furnace. In contrast to the previous results at lower temperature, electrons are transferred from B(6) to Ce at 430 K. X-ray atomic-orbital analysis revealed that the 5d-Gamma(8) orbitals (the energy level of which is similar to that of the B-2p orbitals) are fully occupied and the 4f-Gamma(7) orbitals are more populated than the 4f-Gamma(8) orbitals. Fully occupied 5d-Gamma(8) makes the 4f-Gamma(8) states unstable and the energy levels of 4f-Gamma(7) and 4f-Gamma(8) are inverted.

Synchrotron powder X-ray diffractometer beamline at J. Bennett Johnston, Sr., Center for Advanced Microstructures and Devices

The J. Bennett Johnston, Sr., Center for Advanced Microstructures and Devices (CAMD) is a synchrotron ring operating at 1.3 GeV, with the ring current typically ranging from 230 to 100 mA. An X-ray powder diffraction beamline was recently commissioned at CAMD at the bending magnet port 7A. The powder diffraction beamline consists of a Brazilian-designed double crystal monochromator, a Huber four-circle diffractometer, and a Canberra germanium solid-state detector. The monochromator is equipped with Si 111 and Ge 220 crystals. The Canberra high purity germanium solid-state detector has a resolution of 130 eV at Mn K α. For typical use, the diffractometer circle is set to 17 cm, and the source and receiving slits have been set to 300 and 200 μm, respectively. A sample spinner is used for improved particle size averaging. Wavelength can be shifted in a matter of minutes. Preliminary runs of NIST standards, for example, lanthanum hexaboride (LaB 6) (SRM 660a), show good performance over a wide two-theta range. Rietveld refinement of novaculite (SiO 2) shows lower residual error for the same mineral compared to that obtained from a run with a conventional X-ray source. At the beamline, the user can use MDI's Jade version 7.5 software. The user also has access to International Center for Diffraction Data's Powder Diffraction File-2 database consisting of more than 163,000 inorganic entries and International Crystal Structure Data's crystal structure database with more than 93,000 entries.

THE CRYSTAL STRUCTURE OF KAMPFITE

The crystal structure of kampfite, ideally Ba 12 (Si 11 Al 5 )O 31 (CO 3 ) 8 Cl 5 , a 31.2329(7), b 5.2398(1), c 9.0966(3) A, β 106.933(2)°, V 1424.2(1) A 3 , Cc , Z = 1, has been solved by direct methods and refined to an R index of 2.3% for 2938 observed (| F o | > 4σ F ) reflections collected with a four-circle diffractometer using Mo K α radiation and a CCD detector. The kampfite structure is based on double layers of tetrahedra, [ T 4 O 8 ] , consisting of six-membered rings oriented parallel to (100). The layers of tetrahedra are connected by slabs of Ba polyhedra composed of a layer of BaO 6 Cl 6 polyhedra, with all of the Ba and Cl atoms sharing a common plane parallel to (100), flanked on either side by a layer of BaO 9 Cl polyhedra. The CO 3 groups lie between the layers of Ba polyhedra and are oriented approximately parallel to (100). The layering of T O 4 tetrahedra and Ba polyhedra is responsible for the perfect {100} cleavage of kampfite. Kampfite is part of the monteregianite-(Y) – wickenburgite series and is structurally and chemically similar to cymrite.

A mini-goniometer for X-ray diffraction studies down to 4 K on four-circle diffractometers equipped with two-dimensional detectors

A `universal' low-temperature device for laboratory X-ray diffractometers equipped with two-dimensional detectors has been developed. Single-crystal data collections can be performed down to 4 K. Owing to its original design, the completeness of the data set is not affected by the limited number of accessible orientations of the sample. Classical structure analysis can therefore be performed as well as high-resolution (high-angle) studies for electron-density analysis. Derived from an idea of Argoud & Muller [J. Appl. Cryst.(1989),22, 584–591], the sample is mounted on a holder magnetically coupled to the diffractometer φ axis. The coupling is achieved by mounting a master magnet in place of the usual goniometer head. This magnet drives a slave magnet fixed on the crystal holder: a two-axis mini-goniometer. This low-temperature arrangement is adaptable to any kappa-geometry single-crystal diffractometer equipped with a two-dimensional detector, and can be placed into various types of cryostat. This paper reports the home-made mechanical design and the performance of this device.

X-ray reciprocal space maps and x-ray scattering topographic observation of GaN layer on GaAs (001) in plasma-assisted molecular beam epitaxy

We have characterized plasma-assisted N+ molecular beam epitaxy-grown polymorphous GaN epitaxial layer on GaAs by x-ray reciprocal mapping using four-circle x-ray diffractometer and a personal computer controlled x-ray scattering topography system by ourselves. x-ray reciprocal mapping indicates that GaN wurtzite epitaxial film was grown along only [1¯1¯1] direction. While GaN wurtzite and zinc-blende crystals were contracted along the surface normal, those of lattice constants were expanded along lateral direction. The values of expansion were larger than our instrumental resolution. The lateral expansion rate of lattice constants in GaN wurtzite was larger than that in GaN zinc blende. It was found that zinc-blende phase was unevenly distributed, but wurtzite one was uniformly distributed by growth condition.