Jekabs Grins | Stockholm University (original) (raw)

Papers by Jekabs Grins

Chemistry of Materials, 2003

ABSTRACT The perovskite-related crystal structure of the compound Sr0.7Y0.3CoO2.62 was determined... 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.

Inorganics

Compounds Sr3−xPrxFe1.25Ni0.75O7−δ with 0 ≤ x ≤ 0.4 and Ruddlesden–Popper n = 2 type structures w... 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...

Materials

The CO2 adsorption on various Prussian blue analogue hexacyanoferrates was evaluated by thermogra... 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-...

Chemistry - A European Journal, 2016

Two electrodes for anodic water oxidation made by direct synthesis of inorganic catalysts onto co... 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.

Properties and local structures of RE2O3-Al2O3-SiO2 (RE=Y, Lu) glasses probed by molecular dynami... more 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

J. Mater. Chem. A, 2015

Substitution by strontium induces significant oxygen deficiency in the crystal lattice of K2NiF4-... 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.

RSC Adv., 2015

Solid-state NMR and powder XRD are employed to quantify the ACP (amorphous calcium phosphate) and... more 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.

Journal of Solid State Chemistry, 2015

Solid State Sciences, 1999

The mixed valence state niobium compound MnNb3O6 was found while studying phase formations in the... 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.

MRS Proceedings, 2002

ABSTRACTA series of derivative compounds based on the layered parent phase CrWN2 have been synthe... 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.

MRS Proceedings, 1988

A comparative study of the isotypic Na2BeSiO4, Na1.8[Ga0.2Zn0.8]SiO4 and Na1.8[Ga0.2Zn0.8]Ge04 st... 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.

Science and Technology of Advanced Materials, 2014

Inorganic chemistry, Jan 23, 2014

The hydride Ba3Si4Hx (x = 1-2) was prepared by sintering the Zintl phase Ba3Si4, which contains S... 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...

The Journal of Physical Chemistry C, 2012

The Journal of Physical Chemistry C, 2010

... Additional support for the dual-phase pore-wall model, as well as the role of CaP clusters fo... 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 ...

Solid State Ionics, 1988

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 a... 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.

Chemistry of Materials, 2003

ABSTRACT The perovskite-related crystal structure of the compound Sr0.7Y0.3CoO2.62 was determined... 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.

Inorganics

Compounds Sr3−xPrxFe1.25Ni0.75O7−δ with 0 ≤ x ≤ 0.4 and Ruddlesden–Popper n = 2 type structures w... 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...

Materials

The CO2 adsorption on various Prussian blue analogue hexacyanoferrates was evaluated by thermogra... 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-...

Chemistry - A European Journal, 2016

Two electrodes for anodic water oxidation made by direct synthesis of inorganic catalysts onto co... 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.

Properties and local structures of RE2O3-Al2O3-SiO2 (RE=Y, Lu) glasses probed by molecular dynami... more 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

J. Mater. Chem. A, 2015

Substitution by strontium induces significant oxygen deficiency in the crystal lattice of K2NiF4-... 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.

RSC Adv., 2015

Solid-state NMR and powder XRD are employed to quantify the ACP (amorphous calcium phosphate) and... more 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.

Journal of Solid State Chemistry, 2015

Solid State Sciences, 1999

The mixed valence state niobium compound MnNb3O6 was found while studying phase formations in the... 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.

MRS Proceedings, 2002

ABSTRACTA series of derivative compounds based on the layered parent phase CrWN2 have been synthe... 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.

MRS Proceedings, 1988

A comparative study of the isotypic Na2BeSiO4, Na1.8[Ga0.2Zn0.8]SiO4 and Na1.8[Ga0.2Zn0.8]Ge04 st... 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.

Science and Technology of Advanced Materials, 2014

Inorganic chemistry, Jan 23, 2014

The hydride Ba3Si4Hx (x = 1-2) was prepared by sintering the Zintl phase Ba3Si4, which contains S... 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...

The Journal of Physical Chemistry C, 2012

The Journal of Physical Chemistry C, 2010

... Additional support for the dual-phase pore-wall model, as well as the role of CaP clusters fo... 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 ...

Solid State Ionics, 1988

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 a... 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.