Abstract Silicon hexaboride is a structurally complex boron-rich ceramic whose diffraction response is highly sensitive to processing history and long-range ordering. Nominal SiB 6 ceramics were prepared from elemental Si and B powders by high-energy ball milling for 1 or 10 h, followed by spark plasma sintering (SPS) between 1,300 and 1,700 °C. Laboratory X-ray diffraction shows that specimens processed at 1,300–1,500 °C retain the established orthorhombic SiB 6 -type framework, whereas the patterns obtained at 1,600–1,700 °C exhibit an abrupt redistribution of intensity and intense low-angle reflections that cannot be described by the orthorhombic cell. The long-period monoclinic metric was first verified by Pawley refinement, after which parent-derived rigid polyhedral motifs were assembled in direct space with PowderSolve. For 1,700-N-1H, the PowderSolve proposal was regularized by diffraction-guided geodesic projection (DGGP), introduced here as an alternating structure-solution strategy. DGGP cycles 1–3 generated a contact-safe connected framework; comparison of coordinated rigid-object alternatives with the experimental low-angle intensities then selected variant A as the definitive cycle-4 reconstruction. The final model contains 20 M 12 /M 15 motifs and seven intercluster sites in the asymmetric unit and uses 27 bounded object-wise advancement variables rather than 777 independent Cartesian coordinates for 259 atoms. The resulting sample-specific structures crystallize in P 2 (no. 3, unique axis b ). The definitive 1,700-N-1H cycle-4 cell is a = 32.536(1) Å, b = 5.19176(4) Å, c = 30.3595(1) Å, β = 110.1602(3)°, and V = 4,814.1(2) Å 3 ; the separately deposited 1,700-N-10H cell is a = 32.493(1) Å, b = 5.1784(1) Å, c = 30.2365(7) Å, β = 110.363(2)°, and V = 4,769.7(2) Å 3 . Both cells contain B 444 Si 74 = 74(SiB 6 ), but their detailed rigid-object configurations are distinct. Strong (304) preferred orientation additionally modulates selected intensities in the polished 1H specimen. Its full-range fixed-coordinate calculation gives R wp = 12.53 %, R wp without background = 6.15 %, and R p = 5.89 %; the deposited 10H constrained refinement over 10.0001–44.9951° gives 11.09 %, 4.65 %, and 6.43 %, respectively. These sample- and range-specific values support chemically coherent, strongly constrained average P 2 models rather than unconstrained atom-by-atom determinations.
Abstract The Zr 2 Fe 12 P 7 -type structure is one of the common structure types of transition metal-rich intermetallic compounds. This structural family is characterized through its broad coloring on the nine crystallographically independent Wyckoff sites. This diverse coloring leads to compounds with distinctly different bonding patterns, i.e., pnictides, tetrelides, halides, and even some hydrides. The Zr 2 Fe 12 P 7 -type phases can geometrically be explained through an easy condensation pattern of trigonal prisms, forming shamrock/windmill-like motifs. A central problem is the crystallographic disorder that can occur along the c axis. These structural features are reviewed in the present work, along with the broad magnetic and transport properties.
A new anhydrous sulfate K-1.5(Pb,Na,square)(0.5)[Cu5O2](SO4)(4) (1) was synthesized in an evacuated silica ampoule. 1 is triclinic, P (1) over bar, a = 8.7357(2), b = 9.4633(3), c = 10.0243(3) angstrom, alpha = 107.080(2), beta = 97.326(2), gamma = 105.831(2)degrees, V = 742.42(4) angstrom(3) and R-1 = 0.027. The crystal structure represents a new structure type based on strongly corrugated [Cu5O2](6+) chains. This feature can be attributed to the flexibility of the [Cu5O2](6+) chain in accommodating 'lone-pair' Pb2+ cations at one of the A sites. The crystal chemistry of known fumarolic minerals and synthetic compounds structurally based on [M5O2](n+) chains is discussed.
A new sodium vanadyl phosphate fluoride, Na5VO(PO4)2F, was isolated via hydrothermal synthesis. Its crystal structure was determined using single-crystal X-ray diffraction data and refined against F2 to R = 0.061. The compound crystallizes in the orthorhombic space group Pbca, with unit cell parameters a = 11.7204(6), b = 10.9986(4), c = 13.6111(5) & Aring;, V = 1,754.58(13) & Aring;3, Z = 8. The crystal structure of Na5VO(PO4)2F features layers of VO5F octahedra and PO4 tetrahedra linked by their vertices. Sodium cations occupy the voids within and between the layers. Magnetically, Na5VO(PO4)2F consists of isolated V4+ ions with spin S = 1/2 and exhibits paramagnetic behaviour down to 2 K. A family with the chemical formula Na5MO1-x(PO4)2F1+x (M = Ti, V, Fe; x = 0 or 1) has been recognised and symmetry relation between its members are discussed.
Crystal growth involving the devitrification of glasses in the system Rb2O-Na2O-CaO-SiO2, prepared by quenching from 1,400 degrees C, was performed at 750 degrees C. The experiments resulted in the formation of the first known crystalline rubidium sodium calcium silicate, with a composition of RbNaCaSi4O10. Powder X-ray diffraction patterns of the bulk material of the synthesized product revealed that the material is almost phase pure, containing only very small amounts of an impurity whose identity remains to be determined. Solid-state characterization of this compound included chemical analysis, single-crystal and powder X-ray diffraction, as well as Raman and IR spectroscopy. The basic crystallographic data are as follows: triclinic symmetry, space group P 1 , a = 7.0713(3) & Aring;, b = 8.2037(5) & Aring;, c = 10.1792(5) & Aring;, alpha = 103.504(5)degrees, beta = 99.967(4)degrees, gamma = 115.399(5)degrees, V = 492.95(5) & Aring;(3), Z = 2. Refinement calculations using anisotropic displacement parameters for all atoms converged to a residual of R(|F|) = 0.0385 for 1767 independent reflections. The compound is a synthetic member of the litidionite group of compounds and isostructural with KNaCaSi4O10. Furthermore, it is related to K2CaSi4O10. From a structural perspective, RbNaCaSi4O10 belongs to the group of the tubular chain silicates. The fundamental building units are loop-branched dreier double chains running parallel to [100]. The Ca-and Na-ions are principally coordinated by five nearest oxygen neighbors in the form of distorted tetragonal pyramids. The pyramids are arranged in band-like elements by sharing common edges and corners. Charge compensation is achieved by the incorporation of the larger ten-fold coordinated rubidium ions into cavities of the heteropolyhedral network. A detailed comparison with isotypic KNaCaSi4O10 is presented and the compositional strain induced by the Rb-K substitution is discussed.
