K Atom (k + atom)

Distribution by Scientific Domains


Selected Abstracts


NEXAFS multiple scattering calculations of KO2

JOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001
M. Pedio
Since many years the oxidation of alkali metals has being attracted much interest due to the catalytic properties of metal promoters and the simple electronic structure of alkali atoms. The alkali-oxides phase diagram indicates that the interaction of oxygen with alkali metals can lead to the formation of different atomic O2- ions and molecular O2 - and O22- ions. Potassium superoxide has been prepared in situ and high resolution O k-edge absorption NEXAFS spectra have been measured at the VUV beam-line at ELETTRA facility. The experimental data have been analyzed by multiple scattering approach deriving many geometrical and electronic details. In particular, we have found that the growth material structure is of the KO2 type with an O-O distance of about 1.35Å and that the transition involving single , molecular empty state of the superoxide O2 - anion has a fine structure. Multiple Scattering self consistent calculation indicates that the bond between oxygen anion and K atom is totally ionic and that the fine structure is essentially due to solid state effects. [source]


Growth and single-crystal refinement of phase-III potassium nitrate, KNO3

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2009
Evelyn J. Freney
Oriented single crystals of the high-temperature phase of KNO3 (phase III), a ferroelectric compound that may also occur as an atmospheric aerosol particle, were grown at room temperature and pressure by atomizing a solution of KNO3 in water and allowing droplets to dry on a glass substrate. The crystals are up to 1,mm across and are stable unless mechanically disturbed. There is no evidence of the spontaneous transformation of phase III to the room-temperature stable phase (phase II), even after several months. Single-crystal structure determinations of phase III were obtained at 295 and 123,K. The unit cell regained its room-temperature dimensions after warming from 123,K. The phase-III KNO3 structure can be viewed as the stacking parallel to the c axis of alternating K atoms and planar NO3 groups. The NO3 groups connect the planes of K atoms, where each O is fourfold coordinated to one N and three K. Each K atom has nine O nearest neighbors, with three bonds at 2.813 and six at 2.9092,Å. The interatomic K,N,K distance alternates from 5.051 to 3.941 along the c axis. The N,O distances increase from 1.245,(2),Å at 295,K to 1.2533,(15),Å at 123,K. The nitrate group has a slight non-planarity, with the N atoms 0.011,Å above the O plane and directed toward the more distant K of the K,N,K chain. [source]


12-Membered borophosphate rings in KNi5[P6B6O23(OH)13]

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 12 2009
Olga V. Yakubovich
The title compound, potassium pentanickel hexaborophosphate tridecahydroxide, was synthesized under hydrothermal conditions from the NiCl2,K3PO4,B2O3,K2CO3,H2O system. The crystal structure was determined using single-crystal X-ray diffraction at 100,K. The KNi5[P6B6O23(OH)13] phase is cubic. For the three crystallographically distinct Ni centers, two occupy sites with 3 symmetry, while the third Ni and the K atom are located on sites. The structure is built from alternating borate and phosphate tetrahedra forming 12-membered puckered rings with K+ ions at the centers. These rings are arranged as in cubic dense sphere packing. A novel feature of the new crystal structure is the presence of linear trimers of face-sharing [NiO6] octahedra occupying the octahedral interstices of this sphere packing, and of single [NiO6] octahedra in the tetrahedral interstices. All oxygen corners of the Ni octahedra are linked to phosphate or borate tetrahedra of the 12-membered rings to form a mixed anionic framework. [source]


K3(Sc0.875Nb0.125)Nb2O9H1.75: a new scandium niobate with a unique cage structure

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2009
Matthew Mann
Potassium scandium niobate hydroxide, K3(Sc0.875Nb0.125)Nb2O9H1.75, is a new scandium niobate with a unique cage structure. The structure contains two non-equivalent K+ sites (3m and m2 site symmetry), one disordered Sc3+/Nb5+ site (m site symmetry), one Nb5+ site (3m site symmetry), two O2, sites (m and mm2 site symmetry) and one H+ site (m site symmetry). Both scandium and niobium have octahedral environments, which combine to form cages around potassium. One K atom lies in a cube-like cage built of seven octahedra, while the other K atom is encapsulated by an eight-membered trigonal face-bicapped prism. The cages form sheets that extend along the ab plane. [source]


Synthesis of the Clathrate-II K8.6(4)Ge136 by Oxidation of K4Ge9 in an Ionic Liquid

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2009
Arnold M. Guloy
Abstract The new clathrate-II K8.6(4)Ge136 has been synthesized by mild oxidation of K4Ge9 in the ionic liquid n -dodecyltrimethylammonium chloride (DTAC)/AlCl3 at 300 °C and subsequent annealing at 370 °C. Refinement of the crystal structure from X-ray powder diffraction data revealed the composition K8.6(4)Ge136 [space group Fdm, a = 15.302(1) Å], which was also confirmed by energy-dispersive X-ray spectrometry (EDXS), transmission electron microscopy, and scanning electron microscopy on the bulk material. K atoms preferably occupy the larger Ge28 cages rather than the Ge20 cages in the clathrate-II structure. K8.6(4)Ge136 is metastable and was found to decompose exothermically at 471 °C. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]


Towards a generalized vision of oxides: disclosing the role of cations and anions in determining unit-cell dimensions

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2010
Ángel Vegas
Theoretical calculations of the electron-localization function show that, at the volumes of the two CaO phases (rocksalt and CsCl type), the parent Ca structures (fcc: face-centred cubic and sc: simple cubic, respectively) exhibit charge concentration zones which coincide with the positions occupied by the O atoms in their oxides. Similar features, also observed for the pairs Ca/CaF2 and BaSn/BaSnO3, are supported by recent high-pressure experiments as well as electron-localization function (ELF) calculations, carried out on elemental K. At very high pressures, the elemental K adopts the hP4 structure, topologically identical to that of the K atoms in high-pressure K2S and high-temperature ,-K2SO4. Moreover, the ELF for the hP4 structure shows charge concentration (,,2 electrons) at the sites occupied by the S atoms in the high-pressure K2S phase. All these features confirm the oxidation/high-pressure equivalence as well as the prediction of how cation arrays should be metastable phases of the parent metals. For the first time to our knowledge, the structure type, dimension and topology of several oxides and fluorides (CaO, CaF2 and BaSnO3) are explained in univocal physical terms. [source]


Growth and single-crystal refinement of phase-III potassium nitrate, KNO3

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2009
Evelyn J. Freney
Oriented single crystals of the high-temperature phase of KNO3 (phase III), a ferroelectric compound that may also occur as an atmospheric aerosol particle, were grown at room temperature and pressure by atomizing a solution of KNO3 in water and allowing droplets to dry on a glass substrate. The crystals are up to 1,mm across and are stable unless mechanically disturbed. There is no evidence of the spontaneous transformation of phase III to the room-temperature stable phase (phase II), even after several months. Single-crystal structure determinations of phase III were obtained at 295 and 123,K. The unit cell regained its room-temperature dimensions after warming from 123,K. The phase-III KNO3 structure can be viewed as the stacking parallel to the c axis of alternating K atoms and planar NO3 groups. The NO3 groups connect the planes of K atoms, where each O is fourfold coordinated to one N and three K. Each K atom has nine O nearest neighbors, with three bonds at 2.813 and six at 2.9092,Å. The interatomic K,N,K distance alternates from 5.051 to 3.941 along the c axis. The N,O distances increase from 1.245,(2),Å at 295,K to 1.2533,(15),Å at 123,K. The nitrate group has a slight non-planarity, with the N atoms 0.011,Å above the O plane and directed toward the more distant K of the K,N,K chain. [source]


Polymeric potassium di­aqua­hexa-,-cyano-holmium(III)­ruthenium(II) dihydrate

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2003
Jason A. Kautz
The crystal structure of the title bimetallic cyanide-bridged complex, {K[HoRu(CN)6(H2O)2]·2H2O}n, was determined by means of single-crystal X-ray diffraction techniques. The coordination about the central holmium(III) ion is eightfold in a square-antiprismatic arrangement, while the ruthenium(II) ion is octahedrally coordinated. Channels permeating the crystal lattice contain the potassium cations and two zeolitic water mol­ecules. The HoIII and K atoms lie at sites with mm symmetry and the Ru atom is at a site with 2/m symmetry. [source]