12035-89-1Relevant articles and documents
Thermodynamic properties of silicate glasses and melts: II. System SrO-SiO2
Lopatin,Shugurov,Stolyarova,Tyurnina
, p. 1878 - 1884 (2006)
High-temperature mass spectrometry was used to determine the Gibbs energies, activities, and chemical potentials of SrO and SiO2 in glasses and melts of the SrO-SiO2 system in the temperature range 1840-1970 K. Negative deviations fr
Oxidative Dimerisation of Methane over BaCO3, SrCO3 and these Catalysts promoted with Alkali
Aika, Ken-ichi,Moriyama, Takeshi,Takasaki, Nobuhiro,Iwamatsu, Eiji
, p. 1210 - 1211 (1986)
The yield and selectivity for formation of C2 hydrocarbons from CH4 and O2 were 18.2 and 48.4 percent respectively over 2 g of BaCO3 at 1073 K at a CH4 : O2 ratio of 2.0 : 1, whereas the yield and selectivity were 2.5 and 99.5 percent over SrCO3 at 973 K at a CH4 : O2 ratio of 37.9 : 1.
A novel mixed valent chromium-layered oxide with peculiar magnetic properties: Sr4.5Cr2.5O9
Pelloquin,Wahl,Masset,Maignan,Michel,Raveau
, p. 375 - 383 (2000)
A new mixed valent chromium-layered oxide, Sr4.5Cr2.5O9, with a structure closely related to the '0201-1201' structure of the superconducting cuprate TIBa(2-x)La(2+x)Cu2O9, has been synthesized at normal pressure. This orthorhombic phase (a = 10.7 59(2) A, b = 5.4012(1) A, and c = 30.0755(6) A) consists of the regular intergrowth of [Sr2CrO4]0201 blocks and [(Sr0.5Cr0.5)Sr2CrO5]1201 blocks. It differs from the thallium cuprate by the 1:1 ordering of Sr and Cr species within the intermediate layer of the '1201' block, so that at this level CrO4 tetrahedra, containing Cr6+ species, are obtained. Moreover, at the boundary between the '1201' and '0201' blocks, CrO6 octahedra alternate with CrO5 pyramids, both occupied by Cr3+ species. The magnetic measurements show an original metamagnetic transition from an antiferromagnetic to a weak ferromagnetic state. These properties are interpreted in terms of strong intralaye and weak interlayer magnetic couplings between Cr3+ species through a superexchange mechanism. (C) 2000 Academic Press.
The magnetoelectric perovskite Sr3Fe2TeO9: An insight from magnetic measurements and neutron powder diffraction
Ivanov,Nordblad,Eriksson,Tellgren,Rundl?f
, p. 776 - 789 (2007)
A study of the crystallographic and magnetic structures of the double perovskite Sr3Fe2TeO9 has been carried out on a polycrystalline sample using neutron powder diffraction (NPD) data between 10 and 650 K. An analysis of the NPD patterns at room temperature has shown that this compound crystallises in the tetragonal space group I4/m with a = 5.5614(7) ? and c = 7.867(1) ? and has a partially ordered arrangement of Fe and Te at the B-sites. The compound undergoes an I4/m → Fm-3m improper ferroelectric phase transition near 460 K. A low-temperature ferrimagnetic ordering (below TN = 260 K) has been followed from the magnetisation measurements and sequential NPD data analysis. In good agreement with magnetic measurements the ferrimagnetic structure with very weak magnetisation is defined by the propagation vector k = (0, 0, 0). In addition to the obtained experimental results on magnetic and electric properties some aspects of magnetoelectricity in this perovskite are also discussed and compared with those of another quaternary oxide Sr3Fe2B6+O9.
Kinetics of free-surface decomposition of magnesium, strontium and barium carbonates analyzed thermogravimetrically by the third-law method
L'vov, Boris V.,Ugolkov, Valery L.
, p. 13 - 18 (2004)
The results of our thermogravimetric experiments on the decompositions of MgCO3, SrCO3 and BaCO3 powders and some data reported in the literature were used for the determination of the E parameter of the Arrhenius equation by the third-law method and estimation of the self-cooling effect on the results of these determinations. The experimental values of the E parameters for these carbonates (218, 286 and 302 kJ mol -1) are much higher than the enthalpies of equilibrium reactions (up to solid oxide and CO2) and the values accepted by TA community as the reference data. At the same time, these data are in a good agreement with the mechanism of congruent dissociative evaporation of carbonates with the simultaneous condensation of low-volatility oxides. Differences in the magnitudes of the τ parameter responsible for the consumption of condensation energy by the reactant are revealed. Instead of expected 0.50, the magnitudes of the τ parameter for Mg, Sr and Ba carbonates are as follows: 0.47, 0.42 and 0.10.
Synthesis and Crystal Chemistry of a New Manganite Member Bi3.6Sr12.4Mn8O28+δ,n=2 of the [Bi2Sr2MnO6]n[Sr8Mn 6O16+δ]-Related Tubular Family
Pelloquin,Michel,Maignan,Hervieu,Raveau
, p. 278 - 289 (1998)
A manganite with a tubular structure derived from the 2201-type, Bi3.6Sr12.4Mn8O28+δ, has been synthesized. Its complex crystal chemistry has been studied using XRD, ND, and HREM techniques. It crystallizes in an orthorhombic cell, space groupPbnb, witha=5.4946 A,b=23.595(1) A, andc=23.580(1) A. This structure can be described as an intergrowth, along b, of two types of (010) slices: 2201 -type slices [Bi2Sr2MnO6] that are two octahedra thick and manganese-deficient perovskite-related slices [Sr8Mn6O16+δ] that are one octahedron thick. A similar stacking is observed along c, which endows the structure with a pseudotetragonal character. Another way to describe this structure is to consider criss-crossing layers of manganese polyhedra forming tubes, where the [BiO] rows are inserted, and oxygen-deficient pillars, built up of four Mn polyhedra. This phase represents then=2 member of a new tubular family [Bi2Sr2MnO6]n[Sr8Mn 6O16+δ]. Intergrowth and shearing mechanisms arise along the b and c directions, in agreement with the pseudotetragonal character of the structure. The investigation of the transport and magnetic properties of this new manganite shows that it is an insulator and exhibits weak antiferromagnetism at low temperature (θp=-650 K); the high-temperature data evidence an effective magnetic moment of 4.7μBcharacteristic of high-spin Mn3+(μth=4.9μB).
Synthesis and structure of cobalt (II) oxide halides - Sr2CoO2X2 (X=Cl, Br)
Knee, Christopher S.,Weller, Mark T.
, p. 1 - 4 (2002)
The first layered cobalt (II) oxide halides, Sr2CoO2Cl2 and Sr2CoO2Br2, have been synthesized and their structures determined from Rietveld refinement of powder X-ray data. The materials are structural analogues of the K2NiF4 cuprate phase Sr2CuO2Cl2, crystallizing in space group I4/mmm. The compounds contain CoO2 square planes separated by SrX layers (X=Cl,Br). The bromide material displays the expected increase in cell dimensions, i.e., for Sr2CoO2Cl2, a = 4.06251(5) A, c = 15.1251(3) A and for Sr2CoO2Br2, a = 4.08891(7) A, c = 16.4077(4) A.
Synthesis, crystal structure, and magnetic properties of a novel layered manganese oxide Sr2MnGaO5+δ
Abakumov,Rozova,Pavlyuk,Lobanov,Antipov,Lebedev,Van Tendeloo,Ignatchik,Ovtchenkov,Koksharov,Vasil'ev
, p. 353 - 361 (2001)
New Sr2MnGaO4.97 complex oxide was synthesized by solid state reaction in sealed silica tubes at 950-1000°C. The Sr2MnGaO4.97 crystal structure was refined from X-ray powder diffraction data. Sr2MnGaO4.97 is based on the Ima2 brownmillerite-type structure with apically elongated MnO6 octahedra due to a Jahn-Teller effect. Electron diffraction and high-resolution electron microscopy showed that local ordering of the left- and right-hand chains of GaO4 tetrahedra in Sr2MnGaO4.97 leads to a superstructure with a doubling of the b parameter of the orthorhombic unit cell. The formal oxidation state of Mn (VMn) can be varied by thermal treatments at elevated oxygen pressure (450°C, 20 bar of O2). The oxygen insertion induces a structure transformation in oxidized Sr2MnGaO5.47 material with the formation of a tetragonal perovskite-like structure (a ≈ ap, c ≈ 2cp) with oxygen vacancies located in the Ga layers. The oxidation is accompanied by a significant compression of the Mn-O apical distances and a suppression of the Jahn-Teller deformation. Both Sr2MnGaO4.97 and Sr2MnGaO5.47 can probably be treated as canted antiferromagnets with TN～150 and 80 K, respectively.
Kinetics of dehydration and thermal decomposition of Sr(NO3)2 ·4H2O and its deuterated analogue with a view to obtaining SrO
Maneva,Petroff
, p. 447 - 454 (1988)
The kinetics and mechanism of the thermal-dehydration of Sr(NO3). 4H2O and its deuterated analogue were studied by means of the DTA, TG and DSC. The temperatures, enthalpies and weight losses of phase transitions were measured. The dehydration occurs in a stepwise manner, and the composition of the intermediate depends on the rate of thermal decomposition. The kinetic parameters (E* and Z) for the two steps of dehydration at a heating rate of 5 deg min-1 were calculated. A correlation was found between the disperity of the end-product of the thermal decomposition (SrO) and the conditions of its preparation.
Kinetics and mechanism of free-surface decomposition of solid and melted AgNO3 and Cd(NO3)2 analyzed thermogravimetrically by the third-law method
L'vov, Boris V.,Ugolkov, Valery L.
, p. 7 - 13 (2004)
The third-law method and the retardation effect of the excess of gaseous product in the reactor were used for thermogravometric (TG) investigation of kinetics and mechanisms of thermal decomposition of AgNO3 and Cd(NO3)2. The most important results of this study are formulated as follows. (i) In contrast to AgNO3, the evolution of oxygen in the process of decomposition of Cd(NO3)2 proceeds in the form of free atoms (O). This explains, in particular, the absence of O2 molecules in primary products of Cd(NO 3)2 decomposition revealed earlier by quadrupole mass spectroscopy (QMS). (ii) The decomposition rate is reduced after reactant melting because of the absence of product/reactant interface and associated transfer of condensation energy to the reactant. This conclusion is supported by a rise of the E parameter of the Arrhenius equation by about 20 kJ mol -1 after melting of AgNO3 and Cd(NO3) 2. (iii) The absence of layer of solid product in case of decomposition of melt provides conditions for a free evaporation in vacuum of all primary products including the low-volatility species. This phenomenon was observed in experiments on decomposition of AgNO3 melt in vacuum.
Coupled anion and cation ordering in Sr3RFe4O 10.5 (R=Y, Ho, Dy) anion-deficientperovskites
Abakumov, Artem M.,D'Hondt, Hans,Rossell, Marta D.,Tsirlin, Alexander A.,Gutnikova, Olga,Filimonov, Dmitry S.,Schnelle, Walter,Rosner, Helge,Hadermann, Joke,Van Tendeloo, Gustaaf,Antipov, Evgeny V.
, p. 2845 - 2854 (2010)
The Sr3RFe4O10.5 (R=Y, Ho, Dy) anion-deficient perovskites were prepared using a solid-state reaction in evacuated sealed silica tubes. Transmission electron microscopy and 57Fe Mssbauer spectroscopy evidenced a complete A-cations and oxygen vacancies ordering. The structure model was further refined by ab initio structure relaxation, based on density functional theory calculations. The compounds crystallize in a tetragonal a≈2√2ap≈11.3 A, ≈4p≈16A unit cell (ap: parameter of the perovskite subcell) with the P42/mnm space group. Oxygen vacancies reside in the (FeO5/4□3/4) layers, comprising corner-sharing FeO4 tetrahedra and FeO5 tetragonal pyramids, which are sandwiched between the layers of the FeO 6 octahedra. Smaller R atoms occupy the 9-fold coordinated position, whereas the 10-fold coordinated positions are occupied by larger Sr atoms. The Fe sublattice is ordered aniferromagnetically up to at least 500 K, while the rare-earth sublattice remains disordered down to 2 K.
Koga, Nobuyoshi,Tanaka, Haruhiko
, p. 177 - 188 (1988)
Preparation, crystal structure, and magnetic studies of a new Sr7Re4O19double oxide and its relation to the structure of Ba7Ir6O19
Bramnik,Ehrenberg,Fuess
, p. 45 - 49 (2001)
The complex oxide Sr7Re4O19has been synthesized and its crystal structure was determined by X-ray diffraction powder data analysis (space group C2/m; a=13.6379(3) A, b=5.6035(2) A, c=10.3700(3) A; β=98.348(2)°, Z=2, RI=0.018, Rp=0.050). The compound crystallizes in a new structure type, which can be derived from the Ba7Ir6O19 structure by removing the Ir atoms from the middle octahedron of three face-sharing IrO6octahedra units. This change results in the infinite cis-bridged chains of the ReO6 octahedra linked together by common corners. Each chain is connected with another one by the corner-sharing of each second ReO6octahedron. The 10- and 12-coordinated Sr atoms are situated between these infinite structure fragments. Magnetic properties of the Sr7Re4O19 compound were studied by SQUID measurements.
Mixed Tishchenko reaction over solid base catalysts
Seki, Tsunetake,Kabashima, Hajime,Akutsu, Kazumasa,Tachikawa, Hiroto,Hattori, Hideshi
, p. 393 - 401 (2001)
Catalytic behaviors of solid base catalysts for mixed Tishchenko reactions were investigated to elucidate the activity- and selectivity-determining factors in active sites of the catalysts and molecular structures of the reactants. A mixture containing equal amounts of two kinds of aldehydes was allowed to react at 353 K. The aldehydes used were benzaldehyde, pivalaldehyde, and cyclopropanecar-baldehyde. For all the reactions, the catalytic activity of alkaline earth oxides increased in the order of BaO ? MgO 2O3, ZrO2, ZnO, γ-alumina, hydrotalcite, KF/alumina, and KOH/alumina, were all inactive for the mixed Tishchenko reaction of benzaldehyde and pivalaldehyde; not only crossed-condensation products but also self-condensation products hardly formed. Quantum chemical calculations of the positive charges on the carbonyl carbon atoms of aldehydes and the structure parameters of the active species for the ester formations account for the observed selectivities to four Tishchenko dimers. The selectivities to four Tishchenko dimers over MgO and CaO are determined primarily in the step of the nucleophilic addition of the active species (PhCH2O-, tBuCH2O-, and C3H5CH2O-) to the carbonyl carbon atoms of aldehydes. The reaction of the aldehyde having a more positively charged and sterically less-hindered carbonyl carbon atom with the active species having a less-hindered oxygen atom proceeds faster.
Extension of the 1201 family to strontium-rich chromite and ferrite, Bi0.4Sr2.5Cr1.1O4.9 and Bi0.4Sr2.5Fe1.1O5
Allix,Pelloquin,Studer,Nguyen,Wahl,Maignan,Raveau
, p. 48 - 58 (2002)
Two new Sr-rich 1201 -type oxides, Bi0.4Sr2.5Cr1.1O4.9 and Bi0.4Sr2.5Fe1.1O5 have been synthesized. These compounds, intergrowths of double rock-salt layers with single perovskite layers, show a 1:1 ordering between (Bi,M) and Sr species within the intermediate rock-salt layer [Bi0.4M0.1Sr0.5O]. The XANES study shows that bismuth is mainly trivalent, whereas iron is mixed valent containing 50% Fe3+ and 50% Fe4+ (also confirmed by Moessbauer), and chromium could be a mixture of Cr3+ and Cr6+ sitting inthe perovskite and rock-salt-type sites, respectively. Both compounds exhibit antiferromagnetic interactions. The Cr-phase is a strong insulator, whereas the Fe-phase exhibits a semi-conductor-like resistivity whose value at room temperature is close to that of isotypic cobaltite.
Synthesis and thermal study of 8-hydroxy-quinoline derivatives of the alkaline Earth metals: I. Strontium complexes
Guerreiro,Ribeiro,Crespi,Torres
, p. 519 - 524 (1999)
Strontium complexes of 5,7-dibromo-, 5,7-dichloro-, 7-iodo- and 5-chloro-7-iodo-8-hydroxyquinoline were precipitated from an aqueous ammonia and acetone medium. The complexes obtained were Sr[(C9H4ONBr2)2]·2.5H 2O; Sr[(C9H4ONCl2)(OH)]·1.5H2O; Sr[(C9H5ONI)2]·5H2O and Sr[(C9H4ONICl)(OH)]·1.25H2O. The residues of their thermal decomposition were SrBr2; a mixture of SrCl2, SrCO3 and SrO3 SrCO3, and SrCO3, respectively. All were characterized by means of thermogravimetry, differential thermal analysis, complexometry with EDTA, atomic absorption spectroscopy, IR spectroscopy and X-ray diffraction.
Variation of physical properties in the nominal Sr4V 2O6Fe2As2
Sefat, Athena S.,Singh, David J.,Ovidiu Garlea,Zuev, Yuri L.,McGuire, Michael A.,Sales, Brian C.
, p. 143 - 149 (2011)
We show using a combination of powder X-ray and neutron diffraction, first-principles calculations, temperature- and field-dependent magnetization, heat capacity and resistivity data that the superconducting behavior of 'Sr 4V2O6Fe2As2' is dependent on synthesis conditions, particularly, heating profiles result in unintentional chemical doping. This compound can be tuned from a state in which the vanadium electrons are itinerant with a high electronic density of states, to a state where the vanadium-oxide layers are insulating and presumably magnetic.
Application of non-arrhenius method for analyzing the decomposition kinetics of SrCO3 and BaCO3
Maitra, Saikat,Bandyopadhyay, Narayan,Pal, Jayita
, p. 337 - 341 (2008)
The nonisothermal kinetics of thermal decomposition of SrCO3 and BaCO3 was studied by thermo-gravimetry following non-Arrhenius integral approach of Harcourt and Esson. Variation of activation energy of these two carbonates with frac
Synthesis, physical and photo electrochemical characterization of La-doped SrSnO3
Hadjarab,Bouguelia,Trari
, p. 1491 - 1499 (2007)
The transport properties of Sr0.98La0.02SnO3-δ in the system Sr1-xLaxSnO3-δ, after which the pyrochlore La2Sn2O7 appears, were investigated over the temperature range 4.2-300 K. The oxide was found to be n-type semiconductor with concomitant reduction of Sn4+ into Sn2+. The magnetic susceptibility was measured down to 4.2 K and is less than 3×10-5 emu cgs mol-1 consistent with itinerant electron behavior. The electron is believed to travel in a narrow band of Sn:5s character with an effective mass ～4 mo. The highest band gap is 4.32 eV and the optical transition is directly allowed. A further indirect transition occurs at 4.04 eV. The electrical conductivity follows an Arrhenius-type law with a thermal activation of 40 meV and occurs by small polaron hopping between nominal states Sn4+/2+. The linear increase of thermo-power with temperature yields an electron mobility μ300 K (2×10-4 cm2 V-1 s-1) thermally activated. The insulating-metal transition seems to be of Anderson type resulting from random positions of lanthanum sites and oxygen vacancies. At low temperatures, the conduction mechanism changes to a variable range hopping with a linear plot Ln ρ-1 vs. T-4. The photo electrochemical (PEC) measurements confirm the n-type conductivity and give an onset potential of -0.46 VSCE in KOH (1 M). The Mott-Schottky plot C-2-V shows a linear behavior from which the flat band potential Vfb=+0.01 VSCE at pH 7 and the doping density ND=1.04×1021 cm-3 were determined.
Constitution of the Sr-Ni-O system
Zinkevich
, p. 2818 - 2824 (2005)
The constitution of the Sr-Ni-O system was studied experimentally for the first time. Samples were prepared either from SrCO3 and NiO or from Sr(NO3)2 and Ni(NO3)2·6H 2O and characterized by high-temperature X-ray powder diffraction, scanning electron microscopy, thermogravimetric and differential thermal analyses. In the SrO-NiO quasibinary system an eutectic reaction: liquid?SrO+NiO was found to occur at 1396±5°C, while the homogeneity range of terminal solid solutions is negligible. Thermodynamic calculations using the regular solution model for the liquid and rocksalt-type phases were employed to predict liquidus and solidus curves. Three ternary compounds, SrNiO2.5, Sr5Ni4O11, and Sr9Ni7O21 were observed in the samples prepared from nitrate solutions, but only Sr9Ni7O21 was proved to be thermodynamically stable in air up to 1030±6°C. When heating in air, SrNiO2.5 and Sr5Ni4O 11 were found to transform irreversibly into a mixture of Sr 9Ni7O21 and NiO. Isothermal section of the SrO-NiO-O subsystem, which represents phase equilibria at 950-1030°C as well as an isobaric section of the Sr-Ni-O system in air were constructed.
The standard enthalpies of formation of hydroxides, I. The alkaline-earth hydroxides β-Ba(OH)2 and Sr(OH)2
Konings, R. J. M.,Cordfunke, E. H. P.,Ouweltjes, W.
, p. 989 - 992 (1988)
The enthalpies of solution of β-Ba(OH)2(s) and Sr(OH)2(s) in 1.0109 mol*dm-3 HCl(aq) have been measured.From the results the standard molar enthalpies of formation have been calculated: ΔfH0mβ-Ba(OH)2, s, 298.1
Peculiarities of CaCO3, SrCO3 and BaCO3 decomposition in CO2 as a proof of their primary dissociative evaporation
L'vov, Boris V.,Ugolkov, Valery L.
, p. 47 - 55 (2004)
The results of thermogravimetric experiments on the decompositions of CaCO3, SrCO3 and BaCO3 in the presence of CO2 and some data reported in the literature were used for the determination of the E parameter of the Arrhenius equation by the third-law method. The values obtained (495, 569 and 605kJmol-1) are twice as much compared with the values of the E parameter obtained for these carbonates earlier in the absence of CO2. This fact together with the invariance of the E parameter with partial pressure of CO2 (P CO2) and a hyperbolic dependence of the rate of decomposition on PCO2 is in excellent agreement with the theoretical predictions deduced from the mechanism of decomposition that includes the primary stage of dissociative evaporation of reactant.
Comparative study of oxygen double exchange between O2 adsorbate and alkaline-earth oxides
Huzimura, Ryoitiro,Matsumura, Keiko,Yamabe, Shinichi,Yanagisawa, Yasunori
, p. 13480 - 13483 (1996)
Thermal desorption of doubly exchanged oxygen molecules at temperatures above 800 K is observed not from MgO but from CaO and SrO powders after 18O2-gas exposure at room temperature. The exchange reaction was investigated using ab initio molecular-orbital calculations. The defective (111) surface clusters of CaO and SrO were found to prepare anion-charged reactive centers to accept the O2 adsorbate. The adsorbate was incorporated into a key O5-charged intermediate which can provide an oxygen molecule composed of two lattice atoms for desorptipn. The nonreactive character of the MgO surface in the ground state is ascribed to the presence of oxygen ions bound strongly at the lattice points.
Smith, A. L.,Rosenstein, R. D.,Ward, R.
, p. 1725 - 1729 (1947)
The topotactic reduction of Sr3Fe2O 5Cl2-square planar Fe(II) in an extended oxyhalide
Dixon, Edward,Hayward, Michael A.
, p. 9649 - 9654 (2010)
The topotactic reduction of the oxychloride Sr3Fe 2O5Cl2 with LiH results in the formation of Sr3Fe2O4Cl2. Neutron powder diffraction data show that Sr3Fe2O4Cl 2 adopts a body-centered tetragonal crystal structure (I4/mmm, a = 4.008(1) A, c = 22.653(1) A at 388 K) with anion vacancies located within the SrO layer of the phase. This leads to a structure consisting of infinite sheets of corner-sharing Fe(II)O4 square planes. Variable-temperature neutron diffraction data show that Sr3Fe 2O4Cl2 adopts G-type antiferromagnetic order below TN ～ 378(10) K with an ordered moment of 2.81(9) μB per iron center at 5 K consistent with the presence of high-spin Fe(II). The observed structural and chemical selectivity of the reduction reaction is discussed. The contrast between the structure of Sr 3Fe2O4Cl2 and the isoelectronic all-oxide analogue (Sr3Fe2O5) suggests that by careful selection of substrate phases, the topotactic reduction of complex transition metal oxychlorides can lead to the preparation of novel anion-deficient phases with unique transition metal-oxygen sublattices which cannot be prepared via the reduction of all-oxide substrates.
Crystal and Electronic Structures of A2NaIO6Periodate Double Perovskites (A = Sr, Ca, Ba): Candidate Wasteforms for I-129 Immobilization
Dixon Wilkins, Malin C.,George, Jonathan,Hyatt, Neil C.,Kim, Eunja,Kirk, Cameron,Knight, Kevin S.,Montoya, Eduardo,O'Sullivan, Sarah E.,Sun, Shi-Kuan,Weck, Philippe F.
, p. 18407 - 18419 (2020/12/23)
The synthesis, structure, and thermal stability of the periodate double perovskites A2NaIO6 (A= Ba, Sr, Ca) were investigated in the context of potential application for the immobilization of radioiodine. A combination of X-ray diffraction and neutron diffraction, Raman spectroscopy, and DFT simulations were applied to determine accurate crystal structures of these compounds and understand their relative stability. The compounds were found to exhibit rock-salt ordering of Na and I on the perovskite B-site; Ba2NaIO6 was found to adopt the Fm-3m aristotype structure, whereas Sr2NaIO6 and Ca2NaIO6 adopt the P21/n hettotype structure, characterized by cooperative octahedral tilting. DFT simulations determined the Fm-3m and P21/n structures of Ba2NaIO6 to be energetically degenerate at room temperature, whereas diffraction and spectroscopy data evidence only the presence of the Fm-3m phase at room temperature, which may imply an incipient phase transition for this compound. The periodate double perovskites were found to exhibit remarkable thermal stability, with Ba2NaIO6 only decomposing above 1050 °C in air, which is apparently the highest recorded decomposition temperature so far recorded for any iodine bearing compound. As such, these compounds offer some potential for application in the immobilization of iodine-129, from nuclear fuel reprocessing, with an iodine incorporation rate of 25-40 wt%. The synthesis of these compounds, elaborated here, is also compatible with both current conventional and future advanced processes for iodine recovery from the dissolver off-gas.
