ABSTRACT The perovskite-related crystal structure of the compound Sr0.7Y0.3CoO2.62 was determined and refined using synchrotron X-ray and neutron powder diffraction, in space group I4/mmm, a = 7.6237(8) Å and c = 15.314(2) Å, to RI =... more
ABSTRACT The perovskite-related crystal structure of the compound Sr0.7Y0.3CoO2.62 was determined and refined using synchrotron X-ray and neutron powder diffraction, in space group I4/mmm, a = 7.6237(8) Å and c = 15.314(2) Å, to RI = 0.041 in the synchrotron data set. It contains layers of CoO6 octahedra, perpendicular to the c axis, alternating with partially disordered oxygen-deficient layers. Further characterization of the structure using electron diffraction and high-resolution electron microscopy showed that an additional superstructure was present in some of the crystallites. The structure represents a new type of layered ordering of oxygen vacancies in oxygen-deficient perovskites. Possible local atom arrangements in the oxygen-deficient layers and the structural relationship to the resembling brownmillerite-type structure for ABO2.5 compounds are discussed.
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Compounds Sr3−xPrxFe1.25Ni0.75O7−δ with 0 ≤ x ≤ 0.4 and Ruddlesden–Popper n = 2 type structures were synthesized and investigated by X-ray and neutron powder diffraction, thermogravimetry, and Mössbauer spectroscopy. Both samples,... more
Compounds Sr3−xPrxFe1.25Ni0.75O7−δ with 0 ≤ x ≤ 0.4 and Ruddlesden–Popper n = 2 type structures were synthesized and investigated by X-ray and neutron powder diffraction, thermogravimetry, and Mössbauer spectroscopy. Both samples, prepared at 1300 °C under N2(g) flow and samples subsequently air-annealed at 900 °C, were studied. The structures contained oxygen vacancies in the perovskite layers, and the Fe/Ni cations had an average coordination number less than six. The oxygen content was considerably higher for air-annealed samples than for samples prepared under N2, 7 − δ = ~6.6 and ~5.6 per formula unit, respectively. Mössbauer data collected at 7 K, below magnetic ordering temperatures, were consistent with X-ray powder diffraction (XRD) and neutron powder diffraction (NPD) results. The electrical conductivity was considerably higher for the air-annealed samples and was for x = 0.1~30 S·cm−1 at 500 °C. The thermal expansion coefficients were measured in air between room temperat...
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The CO2 adsorption on various Prussian blue analogue hexacyanoferrates was evaluated by thermogravimetric analysis. Compositions of prepared phases were verified by energy-dispersive X-ray spectroscopy, infra-red spectroscopy and powder... more
The CO2 adsorption on various Prussian blue analogue hexacyanoferrates was evaluated by thermogravimetric analysis. Compositions of prepared phases were verified by energy-dispersive X-ray spectroscopy, infra-red spectroscopy and powder X-ray diffraction. The influence of different alkali cations in the cubic Fm3m structures was investigated for nominal compositions A2/3Cu[Fe(CN)6]2/3 with A = vacant, Li, Na, K, Rb, Cs. The Rb and Cs compounds show the highest CO2 adsorption per unit cell, 3.3 molecules of CO2 at 20 C and 1 bar, while in terms of mmol/g the Na compound exhibits the highest adsorption capability, 3.8 mmol/g at 20 C and 1 bar. The fastest adsorption/desorption is exhibited by the A-cation free compound and the Li compound. The influence of the amount of Fe(CN)6 vacancies were assessed by determining the CO2 adsorption capabilities of Cu[Fe(CN)6]1/2 (Fm3m symmetry, nominally 50% vacancies), KCu[Fe(CN)6]3/4 (Fm3m symmetry, nominally 25% vacancies), and CsCu[Fe(CN)6] (I-...
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Two electrodes for anodic water oxidation made by direct synthesis of inorganic catalysts onto conductive carbon fibre sheets are evaluated. As catalysts two Co- and Sb-containing phases were tested, that is, Co3 Sb4 O6 F6 and the new... more
Two electrodes for anodic water oxidation made by direct synthesis of inorganic catalysts onto conductive carbon fibre sheets are evaluated. As catalysts two Co- and Sb-containing phases were tested, that is, Co3 Sb4 O6 F6 and the new compound CoSbO4 . The compounds express large differences in their morphology: CoSbO4 grows as thin needles whereas Co3 Sb4 O6 F6 grows as larger facetted crystals. Despite the smaller surface area the latter compound shows a better catalytic performance. When the compound Co3 Sb4 O6 F6 was used it gave a low increase of +0.028 mV h(-1) at an overpotential of η=472 mV after 10 h and a stability of +0.48 mV h(-1) at an overpotential of η=488 mV after 60 h. The leakages of Co and Sb were negligible and only <0.001 at % Co and approximately 0.02 at % Sb were detected in the electrolyte.
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Properties and local structures of RE2O3-Al2O3-SiO2 (RE=Y, Lu) glasses probed by molecular dynamics simulations and solid-state NMR : The role of aluminium and rare-earth ions
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Substitution by strontium induces significant oxygen deficiency in the crystal lattice of K2NiF4-type Nd2−xSrxNiO4−δ at elevated temperatures which, in combination with significant electronic conductivity, implies enhanced mixed... more
Substitution by strontium induces significant oxygen deficiency in the crystal lattice of K2NiF4-type Nd2−xSrxNiO4−δ at elevated temperatures which, in combination with significant electronic conductivity, implies enhanced mixed ionic–electronic transport.
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Solid-state NMR and powder XRD are employed to quantify the ACP (amorphous calcium phosphate) and HCA (hydroxy-carbonate apatite) components grown from three mesoporous bioactive glasses with variable compositions.
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The mixed valence state niobium compound MnNb3O6 was found while studying phase formations in the system MnO-Nb2O5-NbO. It is isostructural with AxNb3O6, x ≤ 1 and A = Na, Ca. Single crystals were obtained by heating MnC2O4 · 2H2O and... more
The mixed valence state niobium compound MnNb3O6 was found while studying phase formations in the system MnO-Nb2O5-NbO. It is isostructural with AxNb3O6, x ≤ 1 and A = Na, Ca. Single crystals were obtained by heating MnC2O4 · 2H2O and Nb2O5 in a flow of H2 at 1300 °C. Monophasic samples were also prepared by heating stoichiometric mixtures of MnO, Nb2O5 and Nb in niobium ampoules under Ar(g) at 1100 °C. The crystal structure of MnNb3O6 (Immm, Z = 4, a = 7.1057(5), b = 10.1420(6), c = 6.5341(5) Å) was refined, using singlecrystal MoKα X-ray diffraction data, to a weighted R value of 0.018 for 329 unique reflections. The structure contains undulating layers of NbO6 octahedra of the type α2[NbO6/2]in the ac-plane, with the octahedra sharing edges along [001]and corners along [100]. Between the layers there are columns along [001]of edge-sharing square MnO8 prisms alternating with columns containing Nb2O8 clusters with an Nb-Nb distance of 2.6163(5) Å. The magnetic susceptibility shows a Curie-Weiss behaviour: χM = C/(T+θ) with θ ≈ −22 K and μeff = 6.0(1) μB for T ≥ ca. 35 K, with a small deviation from this dependence at lower temperatures, indicating Mn2+ ions with localised magnetic moments and antiferromagnetic interactions.
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ABSTRACTA series of derivative compounds based on the layered parent phase CrWN2 have been synthesized using a complexed precursor synthesis route. X-ray diffraction analyses demonstrate that both the chromium and tungsten display mutual... more
ABSTRACTA series of derivative compounds based on the layered parent phase CrWN2 have been synthesized using a complexed precursor synthesis route. X-ray diffraction analyses demonstrate that both the chromium and tungsten display mutual substitution for one another and can also undergo considerable extensive replacement by a wide variety of cation species without significantly altering the original layered structure of the parent dinitride compound. The precursor approach employed here appears to offer a ready technique for exploring compositional phase space in layered nitrides of this type.
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A comparative study of the isotypic Na2BeSiO4, Na1.8[Ga0.2Zn0.8]SiO4 and Na1.8[Ga0.2Zn0.8]Ge04 structures has revealed differences in conduction pathway geometries, and calculations show that the two Na-deficient compounds possess larger... more
A comparative study of the isotypic Na2BeSiO4, Na1.8[Ga0.2Zn0.8]SiO4 and Na1.8[Ga0.2Zn0.8]Ge04 structures has revealed differences in conduction pathway geometries, and calculations show that the two Na-deficient compounds possess larger “bottlenecks”. A conduction mechanism, with Na ions using interstitial sites during migration is suggested.
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The hydride Ba3Si4Hx (x = 1-2) was prepared by sintering the Zintl phase Ba3Si4, which contains Si4(6-) butterfly-shaped polyanions, in a hydrogen atmosphere at pressures of 10-20 bar and temperatures of around 300 °C. Initial structural... more
The hydride Ba3Si4Hx (x = 1-2) was prepared by sintering the Zintl phase Ba3Si4, which contains Si4(6-) butterfly-shaped polyanions, in a hydrogen atmosphere at pressures of 10-20 bar and temperatures of around 300 °C. Initial structural analysis using powder neutron and X-ray diffraction data suggested that Ba3Si4Hx adopts the Ba3Ge4C2 type [space group I4/mcm (No. 140), a ≈ 8.44 Å, c ≈ 11.95 Å, Z = 8] where Ba atoms form a three-dimensional array of corner-condensed octahedra, which are centered by H atoms. Tetrahedron-shaped Si4 polyanions complete a perovskite-like arrangement. Thus, hydride formation is accompanied by oxidation of the butterfly polyanion, but the model with the composition Ba3Si4H is not charge-balanced. First-principles computations revealed an alternative structural scenario for Ba3Si4Hx, which is based on filling pyramidal Ba5 interstices in Ba3Si4. The limiting composition is x = 2 [space group P42/mmm (No. 136), a ≈ 8.4066 Å, c ≈ 12.9186 Å, Z = 8], and for...
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... Additional support for the dual-phase pore-wall model, as well as the role of CaP clusters for accelerating the HCA formation of SBF-soaked MBGs, was provided by Jagadeesan et al.,(46) who demonstrated that the bioactivity of MBGs may... more
... Additional support for the dual-phase pore-wall model, as well as the role of CaP clusters for accelerating the HCA formation of SBF-soaked MBGs, was provided by Jagadeesan et al.,(46) who demonstrated that the bioactivity of MBGs may be enhanced further by incorporation ...
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The system Na 1.8 Be 0.9− x Zn x Si 1.1 O 4 with 0≤ x ≤0.9 is found to exhibit solid solubility at elevated temperatures ( T ≥975 K) over the entire compositional range 0≤ x ≤0.9. X-ray powder patterns of the solid solution phase was... more
The system Na 1.8 Be 0.9− x Zn x Si 1.1 O 4 with 0≤ x ≤0.9 is found to exhibit solid solubility at elevated temperatures ( T ≥975 K) over the entire compositional range 0≤ x ≤0.9. X-ray powder patterns of the solid solution phase was indexed on the basis of an orthorhombic unit cell. The unit cell volume increases linearly when the Be atoms are replaced by Zn atoms. At lower temperatures ( T ≤875 K) a two-phase region is observed for compositions 0.3≤ x ≤0.5. The ionic conductivity of the materials was determined by means of ac impedance measurements; it shows no dependence on composition. E a =0.50 with an estimated error of ±0.02 eV and σ≈5×10 −3 [Ω cm] −1 at 600 K.
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ub.umu.se. Publications. ...
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... Abbas Saeed Hakeem a , Jekabs Grins a and Saeid Esmaeilzadeh Corresponding Author Contact ... The samples were heated up to 1400 °C in 10 min, held there for 1 h, and then heated up to the final temperature and held there for 14 h,... more
... Abbas Saeed Hakeem a , Jekabs Grins a and Saeid Esmaeilzadeh Corresponding Author Contact ... The samples were heated up to 1400 °C in 10 min, held there for 1 h, and then heated up to the final temperature and held there for 14 h, depending on the composition. ...
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In this paper the formation of CaAl 2 O 4 from CaCO 3 Al 2 O 3 powder mixtures has been studied, varying holding times between 1 and 40 h and temperatures between 1300 and 1500 °C. Phase formation was studied in samples both quenched... more
In this paper the formation of CaAl 2 O 4 from CaCO 3 Al 2 O 3 powder mixtures has been studied, varying holding times between 1 and 40 h and temperatures between 1300 and 1500 °C. Phase formation was studied in samples both quenched from the holding ...
Research Interests: Materials Engineering, Physical Chemistry, Biomedical Engineering, Microstructure, Electron Microscopy, and 11 moreElectron Diffraction, Focused Ion Beam, Powder X-Ray Diffraction, CHEMICAL SCIENCES, X ray diffraction, Powder, Microstructures, Solid State Reaction, Rietveld method, X ray powder diffraction, and The European
ABSTRACT Many features of aluminosilicate glasses incorporating a rare-earth (RE) ion are dictated by its mass and cation field strength (CFS). Sc–Al–Si–O glasses are interesting because Sc3+ exhibits the highest CFS but the lowest mass... more
ABSTRACT Many features of aluminosilicate glasses incorporating a rare-earth (RE) ion are dictated by its mass and cation field strength (CFS). Sc–Al–Si–O glasses are interesting because Sc3+ exhibits the highest CFS but the lowest mass of all RE3+ ions. We explore relationships between the glass composition and several physical properties, such as density, glass-transition tempera-ture (Tg), Vickers hardness, and refractive index, over the glass forming region of the ternary Sc2O3–Al2O3–SiO2 system. The glasses exhibit uniform and unexpectedly low Tg -values (≈875°C), but a high microhardness (≈9.3 GPa) that corre-lates with the Sc2O3 content. 29Si magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy shows enhanced deshielding and a minor glass-network ordering as either the Al or Sc content of the glass increases. 27Al MAS NMR reveals that besides the expected AlO4 tetrahedra, substantial amounts of AlO5 (31%–35%) and AlO6 (≈5%) polyhedra are present in all Sc–Al–Si–O glass structures. 45Sc isotropic chemical shifts (92 ppm) derived from MAS and 3QMAS (triple-quantum MAS) NMR experiments are consistent with ScO6 environments.
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The K2ZnGeO4 structure has been refined, from X-ray powder diffractometer data, in space group Pca21 and with the unit cell a = 11.0769(10) Å, b = 5.5216(5) Å, c = 15.8465(13) Å, V = 969.2 Å3, to residual factors RF = 4.9% and Rwp =... more
The K2ZnGeO4 structure has been refined, from X-ray powder diffractometer data, in space group Pca21 and with the unit cell a = 11.0769(10) Å, b = 5.5216(5) Å, c = 15.8465(13) Å, V = 969.2 Å3, to residual factors RF = 4.9% and Rwp = 16.2%. Constraints on the positional parameters (pair-wise linking) were used in order to obtain a
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... 3 Ta 2 O 8 , using synchrotron X-ray powder and electron diffraction data Saeid Esmaeilzadeh,a Jekabs Grinsa and Andy Fitchb ... with a body-centred unit cell, using the TREOR90 version of Bragg peaks was 0.014° at 2h=21.4°. MnTa 2 O... more
... 3 Ta 2 O 8 , using synchrotron X-ray powder and electron diffraction data Saeid Esmaeilzadeh,a Jekabs Grinsa and Andy Fitchb ... with a body-centred unit cell, using the TREOR90 version of Bragg peaks was 0.014° at 2h=21.4°. MnTa 2 O 6 and Mn 4 Ta 2 O 9 ...
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Single crystals of the sialon Ce N-phase Ce3Si8 − xAlxN11 − xO4 + x (x ≈ 1.75) were obtained via a novel route, i.e. by first preparing a fully compacted body with phase constitutions far away from thermal dynamic equilibrium by means of... more
Single crystals of the sialon Ce N-phase Ce3Si8 − xAlxN11 − xO4 + x (x ≈ 1.75) were obtained via a novel route, i.e. by first preparing a fully compacted body with phase constitutions far away from thermal dynamic equilibrium by means of a fast densification technique, spark plasma sintering, and then heat treating this compact in a sialon powder bed at 1600 °C in N2 atmosphere for 24 h. The structure of the Ce N-phase was solved using MoKα single-crystal data and direct methods. It was refined in space group I2/a with a = 15.798(1), b = 4.8939(3), c = 17.990(1) A, β = 114.816(4)°, V = 1262.4 A3, to a weighted R(Fobs2) = 6.7% for 977 unique reflections. The isostructural La phase structure was refined with anisotropic thermal parameters for La and N/O atoms using time-of flight neutron powder diffraction data. The structure exhibits three structural kinds of N/O anions: 4/15 of these are N atoms which are triangularly coordinated by 3 Si/Al atoms, 2/15 are tetrahedron free apex O atoms which are in addition bonded to 3 Ce/La atoms while the remaining 9/15 are on sites that are statistically occupied by N and O atoms and which are bonded to 2 tetrahedral Si/Al atoms and 1–2 Ce/La atoms. Comparisons are made with a previous structural proposal deduced from solid state nuclear magnetic resonance spectra.
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ABSTRACT
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A nitrogen-rich sialon phase containing Sr or Eu, named the S-phase, has been reported to form in the M′-Si-Al-O-N systems with M′=Sr and Eu. A sample with overall composition Sr 2 Al 2.5 Si 10 O 4 N 14.5 hot-pressed at 1800°C for 2 h... more
A nitrogen-rich sialon phase containing Sr or Eu, named the S-phase, has been reported to form in the M′-Si-Al-O-N systems with M′=Sr and Eu. A sample with overall composition Sr 2 Al 2.5 Si 10 O 4 N 14.5 hot-pressed at 1800°C for 2 h contained approximately 85 vol% of the S-phase, and in addition the α- and β-sialon phases and an amorphous phase. Its structure was solved from X-ray synchrotron powder data (λ=1.1608 A), using direct methods, and was refined by the Rietveld method from 131 reflections in the 2θ range 10-59° to R F =2.7%, with the assumed composition Sr 2 Al 2 Si 10 O 4 N 14 , space group Imm2, a=8.2788(9), b=9.5757(9), c=4.9158(4) A, V=389.7 A 3 . The structure model was confirmed by its electron diffraction pattern and by high-resolution electron microscopy studies. The structure exhibits a tetrahedral network with high connectivity, each tetrahedron sharing corners with seven surrounding tetrahedra, and the Sr atoms, irregularly coordinated by eight O/N atoms, are found in tunnels extending along [001].
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The structures of two Nb and two MnNb (oxy) nitrides have been refined from Cu Kα1 powder diffractometer data by the Rietveld method and have been characterised by electron diffraction. The phases Nb3. 49N4. 56O0. 44 and Mn0. 54Nb3.... more
The structures of two Nb and two MnNb (oxy) nitrides have been refined from Cu Kα1 powder diffractometer data by the Rietveld method and have been characterised by electron diffraction. The phases Nb3. 49N4. 56O0. 44 and Mn0. 54Nb3. 07N4. 40O0. 60 have ...
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The mixed valence state niobium compound MnNb3O6 was found while studying phase formations in the system MnO-Nb2O5-NbO. It is isostructural with AxNb3O6, x ≤ 1 and A = Na, Ca. Single crystals were obtained by heating MnC2O4 · 2H2O and... more
The mixed valence state niobium compound MnNb3O6 was found while studying phase formations in the system MnO-Nb2O5-NbO. It is isostructural with AxNb3O6, x ≤ 1 and A = Na, Ca. Single crystals were obtained by heating MnC2O4 · 2H2O and Nb2O5 in a flow of H2 at 1300 °C. Monophasic samples were also prepared by heating stoichiometric mixtures of MnO, Nb2O5 and Nb in niobium ampoules under Ar(g) at 1100 °C. The crystal structure of MnNb3O6 (Immm, Z = 4, a = 7.1057(5), b = 10.1420(6), c = 6.5341(5) Å) was refined, using singlecrystal MoKα X-ray diffraction data, to a weighted R value of 0.018 for 329 unique reflections. The structure contains undulating layers of NbO6 octahedra of the type α2[NbO6/2]in the ac-plane, with the octahedra sharing edges along [001]and corners along [100]. Between the layers there are columns along [001]of edge-sharing square MnO8 prisms alternating with columns containing Nb2O8 clusters with an Nb-Nb distance of 2.6163(5) Å. The magnetic susceptibility shows ...
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ABSTRACT
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Phase formation in the system Zr x Ta 1x (O, N) y has been studied by ammonolysis of Zr-Ta gels, prepared by the solgel technique, at temperatures between 700 and 1000 C. The starting gels and observed phases were characterised by X-ray... more
Phase formation in the system Zr x Ta 1x (O, N) y has been studied by ammonolysis of Zr-Ta gels, prepared by the solgel technique, at temperatures between 700 and 1000 C. The starting gels and observed phases were characterised by X-ray powder ...
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ABSTRACT
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We report physical properties of density, glass transition temperature, Vickers hardness and refractive index for 15 LaAlSiO glasses within the compositional region 1028 mol% La 2 O 3 , 1130% Al 2 O 3 and 4578% SiO 2 . The glass... more
We report physical properties of density, glass transition temperature, Vickers hardness and refractive index for 15 LaAlSiO glasses within the compositional region 1028 mol% La 2 O 3 , 1130% Al 2 O 3 and 4578% SiO 2 . The glass transition temperature varies only ...