- Structural Modification of the Cation-Ordered Ruddlesden-Popper Phase YSr2Mn2O7 by Cation Exchange and Anion Insertion
-
Calcium-for-strontium cation substitution of the a-b0c0/b0a-c0-distorted, cation-ordered, n = 2 Ruddlesden-Popper phase, YSr2Mn2O7, leads to separation into two phases, which both retain an a-b0c0/b0a-c0-distorted framework and have the same stoichiometry but exhibit different degrees of Y/Sr/Ca cation order. Increasing the calcium concentration to form YSr0.5Ca1.5Mn2O7 leads to a change in the cooperative tilting on the MnO6 units to a novel a-b-c-/b-a-c- arrangement described in space group P21/n11. Low-temperature, topochemical fluorination of YSr2Mn2O7 yields YSr2Mn2O5.5F3.5. In contrast to many other fluorinated n = 2 Ruddlesden-Popper oxide phases, YSr2Mn2O5.5F3.5 retains the a-b0c0/b0a-c0 lattice distortion and P42/mnm space group symmetry of the parent oxide phase. The resilience of the a-b0c0/b0a-c0-distorted framework of YSr2Mn2O7 to resist symmetry-changing deformations upon both cation substitution and anion insertion/exchange is discussed on the basis the A-site cation order of the lattice and the large change in the ionic radius of manganese upon oxidation from Mn3+ to Mn4+. The structure property relations observed in the Y-Sr-Ca-Mn-O-F system provide insight into assisting in the synthesis of n = 2 Ruddlesden-Popper phases, which adopt cooperative structural distortions that break the inversion symmetry of the extended lattice and therefore act as a route for the preparation of ferroelectric and multiferroic materials.
- Zhang, Ronghuan,Gibbs, Alexandra S.,Zhang, Weiguo,Halasyamani, P. Shiv,Hayward, Michael A.
-
-
Read Online
- Production of fluorine by the electrolysis of calcium fluoride-containing tetrafluoroborate melts
-
Tetrafluoroborate melts have been shown to be viable electrolytes for the electrochemical production of fluorine from dissolved CaF2. The anode reaction at pyrolytic graphite electrodes apparently involves the oxidation of BF4-
- Mamantov,Laher
-
-
Read Online
- Dinitrogen difluoride chemistry. Improved syntheses of cis- and trans-N2F2, Synthesis and characterization of N 2F+Sn2F9-, ordered crystal structure of N2F+Sb2F11 -, High-level electronic structure calculations of cis-N 2F2
-
N2F+ salts are important precursors in the synthesis of N5+ compounds, and better methods are reported for their larger scale production. A new, marginally stable N2F + salt, N2F+Sn2F9 -, was prepared and characterized. An ordered crystal structure was obtained for N2F+Sb2F11-, resulting in the first observation of individual N - N and N-F bond distances for N2F+ in the solid phase. The observed N - N and N-F bond distances of 1.089(9) and 1.257(8) A, respectively, are among the shortest experimentally observed N-N and N-F bonds. High-level electronic structure calculations at the CCSD(T) level with correlation-consistent basis sets extrapolated to the complete basis limit show that cis-N2F 2 is more stable than trans-N2F2 by 1.4 kcal/mol at 298 K. The calculations also demonstrate that the lowest uncatalyzed pathway for the trans-cis isomerization of N2F2 has a barrier of 60 kcal/mol and involves rotation about the N - N double bond. This barrier is substantially higher than the energy required for the dissociation of N2F2 to N2 and 2 F. Therefore, some of the N2F2 dissociates before undergoing an uncatalyzed isomerization, with some of the dissociation products probably catalyzing the isomerization. Furthermore, it is shown that the trans-cis isomerization of N2F2 is catalyzed by strong Lewis acids, involves a planar transition state of symmetry Cs, and yields a 9:1 equilibrium mixture of cis-N2F2 and trans-N2F2. Explanations are given for the increased reactivity of cis-N2F 2 with Lewis acids and the exclusive formation of cis-N 2F2 in the reaction of N2F+ with F-. The geometry and vibrational frequencies of the F2N - N isomer have also been calculated and imply strong contributions from ionic N2F+ F- resonance structures, similar to those in F3NO and FNO.
- Christe, Karl O.,Dixon, David A.,Grant, Daniel J.,Haiges, Ralf,Tham, Fook S.,Vij, Ashwani,Vij, Vandana,Wang, Tsang-Hsiu,Wilson, William W.
-
p. 6823 - 6833
(2010/09/06)
-
- Vaporization products of transition-metal and rare-earth complex fluorides studied by high-temperature mass spectrometry
-
Gaseous products of the thermal decomposition of Ni(IV), Tb(IV), Mn(IV), and Pt(IV) complex fluorides were studied by high-temperature mass spectrometry. The results demonstrate that the decomposition of potassium hexafluoronickelate and potassium heptafl
- Leskiv,Abramov,Oleinik,Kepman,Sukhoverkhov,Mazej,Rau,Chilingarov,Sidorov
-
p. 1327 - 1333
(2008/10/09)
-
- Thermochemical reactions and equilibria between fluoromicas and silicate matrices: A petromimetic perspective on structural ceramic composites
-
A petromimetic (geological-analog) approach is applied to the design of alumina-fiber-reinforced glass-ceramic-matrix composites that use a refractory, trioctahedral fluoromica fiber-matrix interphase and feldspar matrixes. Studies of the solid-state reaction couples between these silicate phases are pursued to address the chemical tailorability of the interphase/matrix interface from an engineering perspective. The minimization of alumina and silica activities within polyphase, feldspar-based matrixes via MgO buffering is shown to be an effective route toward a stable fluoromica interphase. An anorthite-2-vol%-alumina (CaAl2Si2O8+α-Al2O3) substrate, chemically buffered with MgO, is shown to exhibit thermodynamic stability against fluorokinoshitalite (BaMg3[Al2Si2]O10F2), up to temperatures potentially as high as 1460 °C. The key to the approach is the reduction of alumina activity via the formation of MgAl2O4 spinel. Similarly, the formation of forsterite (Mg2SiO4) stabilizes the mica in contact with matrix compositions otherwise containing excess silica. The cationic interdiffusion between solid-solution feldspars and fluoromicas also is characterized. Coupled interdiffusion of K+ and Si4+ in exchange for Ba2+ and Al3+ was observed between K-Ba solid-solution celsian and the barium-rich solid-solution end-member fluorokinoshitalite at 1300 °C. A similar cationic exchange also is observed against the potassium-rich end-member fluorophlogopite (KMg3[AlSi3]O10F2), although in a reverse direction, at temperatures of 1280 °C. The interfacial compositions identified via electron microprobe analysis specify one set of local equilibrium conditions from which global ceramic composite equilibrium can be achieved.
- King, Todd T.,Grayeski, Walter,Cooper, Reid F.
-
p. 2287 - 2296
(2008/10/08)
-
- Synthesis of Manganese Tetrafluoride at Atmospheric Pressure
-
The fluorination rate of powdery MnF3 is measured by the gravimetric method at 450-540°C, fluorine partial pressure 1.0-10.1 kPa, near-atmospheric total pressure, and the linear rate of (F2 + N2) gas mixture 2.0 cm/s. It is shown that the rate law of fluorination α = 10-0.14exp[-84.7 × 103/RT]ρF20.57τ. A new procedure of MnF4 synthesis from particulate MnF2 and MnF3 in a fluorine flow at atmospheric pressure and the design of a fluorination reactor are described. They are shown to afford relatively high reaction rates (up to 35 g/h based on MnF4) and high yields with respect to fluorine (up to 42%).
- Rakov,Khaustov,Ostropikov
-
p. 465 - 469
(2008/10/08)
-
- Thermal Decomposition and Pyrohydrolysis of Manganese Tetrafluoride
-
Thermal decomposition of MnF4 and its reaction with water vapor are studied by gravimetric, DTA, and TG analyses complemented by chemical and X-ray diffraction analyses of the solid products. The decomposition is found to begin at temperatures higher than 325 K and to proceed with the formation of MnF3 and partial evolution of MnF4. At temperatures below 473 K, the reaction does not reach completion because of kinetic hindrance. Pyrohydrolysis of MnF4 is accompanied by reduction and proceeds stepwise to form first MnF3 · 3H2O and then MnOF.
- Rakov,Khaustov,Pomadchin
-
p. 1646 - 1649
(2008/10/08)
-
- Kinetics of Fluorination of Manganese Compounds with Fluorine Gas
-
The kinetics of fluorination of MnO2, MnF2, and KMnF3 powders by fluorine in nitrogen carrier gas at atmospheric pressure was studied by gravimetry. The kinetic equations of fluorination were deduced. MnO2 converts to MnF3 markedly more rapidly than MnF2. The volatile product (MnF4) forms above 780 K.
- Rakov,Ostropikov,Khaustov
-
p. 149 - 153
(2008/10/08)
-
- Novel type of oxonium salts H3OM(AsF6)3 (M=Mn, Co, Ni): Syntheses, structures and some properties
-
H3OAsF6 reacts with M(AsF6)2 (M=Mn,Co,Ni) in anhydrous hydrogen fluoride (aHF) acidified with AsF5 at room temperature yielding novel oxonium salts H3OM(AsF6)3. If MF2 is used instead of M(AsF6)2 the aHF should be rich in AsF5 to synthesize M(AsF6)2 in situ. As source of the oxonium cation water or the transition metal oxide can be used. X-ray powder diffraction at variable temperatures revealed for H3OCo(AsF6)3 a phase transition at 120K. The high temperature (HT) form crystallizes in the orthorhombic space group Pnma (No.62) with a=1037.6(1), b=1372.6(1), c=932.8(1) pm, V=1.3285(2) nm3, Z=4 and dc=3.223 g/cm3 at 150 K. The low temperature (LT) form crystallizes in the monoclinic space group P21/c (No.14) with a=1032.6(1), b=1370.2(2), c=1867.1(2) pm, β=90.036(9)°, V=2.6416(5) nm3, Z=8, dc=3.242 g/cm3 at 90 K. The structure was solved by direct methods using diffractometer data sets and refined to conventional R1=0.039 for 2604 reflections (HT-form) and R1=0.053 for 9215 reflections (LT-form), respectively. One main feature of the H3OCo(AsF6)3 structure is a ring of four AsF6 octahedra which are connected by four cobalt atoms. This kind of ring system is continued infinitely in the plane and also perpendicular to the plane. In this arrangement open channels are created in which oxonium ions are placed below and above the plane. Gauthier-Villars.
- Lutar,Zemva,Borrmann
-
p. 957 - 969
(2008/10/08)
-
- Observation of the laser induced fluorescence spectra of C2(d3?g 3?u) from the infrared multiphoton dissociation of bis-trifluoromethyl peroxide
-
C2 has been produced by infrared multiphoton dissociation of bis-trifluoromethyl peroxide.The (0,0), (1,0), and (2,0) transition of the Swan system for C2 have been detected using laser induced fluorescence method.The (0,0), (2,0) laser excitation spectra
- Li, Zhuangjie,Francisco, Joseph S.
-
p. 878 - 881
(2007/10/02)
-
- Synthesis and thermal study of tris(ammonium) hexafluoro metallates(III) of some rare earths
-
Fluorination of oxides of rare earths using ammonium hydrogen fluoride at room temperature gave new compounds 3MF6*nH2O, where M = Y, La, Nd, and Pr.In the case of cerium, 4CeF8 is formed.The course of thermal decomposition of all these compounds is studied by thermogravimetry/differential thermal analysis (TG/DTA) and X-ray powder diffraction(XRD).Key words: hexafluoro metallates, rare earths, ammonium hydrogen fluoride, thermal decomposition, X-ray diffraction.
- Patwe, S. J.,Wani, B. N.,Rao, U. R. K.,Venkateswarlu, K. S.
-
p. 1815 - 1818
(2007/10/02)
-
- Thermal stabilities of americium and cerium tetrafluorides
-
The thermal stabilities of americium and cerium tetrafluorides were determined by mass spectrometry, monitoring their gaseous vaporization and/or decomposition products as a function of temperature. For americium tetrafluoride, the dominant high temperature (less than or equal to 700°C) process is thermal decomposition to the trifluoride. In contrast, with cerium tetrafluoride, the most prominent process at high temperature (less than or equal to 850°C) is congruent sublimation. The results of these studies are interpreted in terms of the relevant thermodynamic parameters for each process and are compared with predictions and results which have been reported in the literature.
- Gibson,Haire
-
p. 123 - 131
(2008/10/08)
-
- THERMAL DECOMPOSITION OF CURIUM TETRAFLUORIDE AND TERBIUM TETRAFLUORIDE.
-
The thermal decompositions of both curium and terbium tetrafluorides have been studied using mass spectrometry to monitor the effusate from a Knudsen cell containing the condensed fluoride. Curium tetrafluoride was found to decompose at 330-430 degree C in vacuum. A Second Law enthalpy of 26. 3 plus or minus 2 kcal/mole (at 370 degree C) is derived from van't Hoff plots of results obtained for the decomposition reaction. Decomposition fluorine pressures are derived and comparison is made with related studies of terbium tetrafluoride carried out in conjunction with the curium experiments. The results are compared both with data reported in the literature for lanthanide and actinide tetrafluorides and with predictions that have been made for CmF//4.
- Gibson,Haire
-
p. 524 - 530
(2008/10/08)
-
- On the existence of pentacoordinated nitrogen
-
The thermal decomposition of NF4HF2 was studied by using 18F-labeled HF2-. The observed distribution of 18F among the decomposition products indicates that within experimental error the attack of HF2- on NF4+ occurs exclusively on fluorine and not on nitrogen, contrary to the predictions based on bond polarities. These results confirm the previous suggestion that the lack of pentacoordinated nitrogen species is due mainly to steric reasons.
- Christe, Karl O.,Wilson, William W.,Schrobilgen, Gary J.,Chirakal, Raman V.,Olah, George A.
-
p. 789 - 790
(2008/10/08)
-
- Synthesis and characterization of NF4CrF6 and reaction chemistry of CrF5
-
NF4CrF6, a new stable NF4+ salt containing an energetic counterion, was prepared by treatment of CrF5 with an excess of NF4HF2 in HF solution. The composition and ionic nature of NF4CrF6 was established by elemental analysis, vibrational and 19F NMR spectroscopy, and its X-ray powder pattern. Reactions of CrF5 with H2O in HF, ClF3, FNO, Cl2, CFCl3, and KrF2 were studied to determine its acidity and oxidizing power. With FNO, a stable 1:1 adduct is formed, which on the basis of its vibrational spectra has the ionic structure NO+CrF6-. The reaction of NOCrF6 with NO produced (NO+)2CrF62-, which by controlled pyrolysis was converted to NO+CrF5-. With stoichiometric amounts of H2O in HF, CrF5 did not form a stable OH3+CrF6- salt but the reaction resulted in hydrolysis to CrF3O. The influence of the strong Lewis acids AsF5 and SbF5 on the oxidizing power of CrF5 was also investigated. On the basis of the fact that CrF5-SbF5 mixtures can oxidize O2 (IP = 12.06 eV) but not NF3 (IP = 13.00 eV), the following qualitative oxidizer strength scale is proposed: KrF+ > PtF6 > SbF5 + F2 + activation energy > CrF5-SbF5. The results of a normal-coordinate analysis of CrF6- and CrF62- show the expected decrease in force constants with increasing negative charge.
- Bougon, Roland,Wilson, William W.,Christe, Karl O.
-
p. 2286 - 2292
(2008/10/08)
-
- Synthesis and Characterization of a New Uranium(VI) Compound with a Co-ordination Number Larger than Eight, Ammonium Decafluorouranate(VI)
-
Oxidation of 4UF8 by XeF2 gave a new compound, 4UF10, for which Raman spectra indicate a co-ordination number larger than eight, and infrared spectra show moderate hydrogen bonding.
- Druzina, Branko,Milicev, Svetozar,Slivnik, Joze
-
p. 363 - 364
(2007/10/02)
-
- Chemical and physical properties of some xenon compounds
-
Useful preparative reactions for several xenon compounds can be systematized as acid-base chemistry. The hydrolysis of XeF4 and ammonolysis of XeF6 have been investigated. The melting point of XeO4 and the melting point an
- Huston, John L.
-
p. 685 - 688
(2008/10/08)
-
- Millimetr wave measurements of the rotational spectra of ClF, BrF, BrCl, ICl, and IBr
-
The rotational spectra of all twelve stable isotopic species of ClF, BrF, BrCl, ICl, and IBr were abserved and measured in the millimeter wave region by means of a sensitive microwave spectrometer.Transitions were detected over a wide range of frequencies for molecules in both the ground vibrational state and several excites states.The rotational spectrum of each molecule was split by the nuclear quadrupole interaction.Altogether, 250 new lines were measured.These correspond to 136 purw rotational transitions.Values of the Dunham coefficients Y01, Y11, Y21, Y31, Y02, Y12, and Y03 were obtained from a computer analysis of the measured frequencies.From these coefficients a number of equilibrium constants were derived to significantly greater accuracy than in previous work.In particular, the equilibrium distance, re, was found to two or three more significant figures.
- Willis, Robert E.,Clark, William W.
-
p. 4946 - 4950
(2007/10/02)
-
- Preparation and properties of perfluoroammonium tetrafluoroborate, NF4+BF4-, and possible synthesis of nitrogen pentafluoride
-
A new crystalline compound, NF4+BF4-, has been prepared by exposing the heterogeneous ternary system NF3-BF3-F2 to 3-MeV bremsstrahlung at 77°K. The G value for the reaction (molecules isolated per 100 eV absorbed) is about unity. The compound is stable at room temperature in dry air; it decomposes above 250° to the reactants. It reacts rapidly with moisture and with organic substances. The indicated ionic structure is confirmed by infrared and Raman spectroscopy. The X-ray powder pattern can be indexed on the basis of a tetragonal unit cell with a = 7.01 and c = 5.22 A?. Irradiation of mixtures of nitrogen trifluoride and excess fluorine at 77°K has led to isolation in low yields of a white solid. It decomposes below 143°K to liberate nitrogen trifluoride and reacts with boron trifluoride at low temperature to form NF4BF4. Its most likely identity is perfluoroammonium fluoride.
- Goetschel,Campanile,Curtis,Loos,Wagner,Wilson
-
p. 1696 - 1701
(2008/10/08)
-