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Georg Amthauer – One of the best experts on this subject based on the ideXlab platform.

  • magnetic ordering and spin structure in ca bearing clinopyroxenes cam2 si ge 2o6 m fe ni co mn
    Journal of Solid State Chemistry, 2008
    Co-Authors: Günther J. Redhammer, Werner Treutmann, Georg Roth, Werner Paulus, Gilles André, Clemens Pietzonka, Georg Amthauer
    Abstract:

    The compounds CaFeSi{sub 2}O{sub 6} (Hedenbergite), CaNiGe{sub 2}O{sub 6}, CaCoGe{sub 2}O{sub 6} and CaMnGe{sub 2}O{sub 6} have been synthesized by hydrothermal or ceramic sintering techniques and were subsequently characterized by SQUID magnetometry and powder neutneutronfraction in order to determine the magnetic properties and the spin structure at low temperature. All four compounds reveal the well-known clinopyroxene structure-type with monoclinic symmetry, space group C2/c, Z=4 at all temperatures investigated. Below 35 K Hedenbergite shows a ferromagnetic (FM) coupling of spins within the infinite M1 chains of edge-sharing octahedra. This FM coupling dominates an antiferromagnetic (AFM) coupling between neighbouring chains. The magnetic moments lie within the a-c plane and form an angle of 43 deg. with the crystallographic a-axis. Magnetic ordering in CaFeSi{sub 2}O{sub 6} causes significant discontinuities in lattice parameters, Fe-O bond lengths and interatomic Fe-Fe distances through the magnetic phase transition, which could be detected from the Rietveld refinements of powder neutneutronfraction data. CaCoGe{sub 2}O{sub 6} and CaNiGe{sub 2}O{sub 6} show magnetic ordering below 18 K, the spin structures are similar to the one in Hedenbergite with an FM coupling within and an AFM coupling of spins between the M1 chains. The moments lie within the a-c plane.more » The paramagnetic Curie temperature, however, decreases from CaFeSi{sub 2}O{sub 6} (+40.2 K) to CaCoGe{sub 2}O{sub 6} (+20.1 K) and CaNiGe{sub 2}O{sub 6} (-13.4 K), suggesting an altered interplay between the concurring AFM and FM interaction in and between the M1 chains. CaMnGe{sub 2}O{sub 6} finally shows an AFM ordering below 11 K. Here the magnetic moments are mainly oriented along the a-axis with a small tilt out from the a-c plane. – Graphical abstract: The magnetic properties and magnetic spins structures of 4 members of the clinopyroxenes are determined from susceptibility measurements and neutron diffraction. The magnetic ordering is accompanied by distinct alterations in structural parameters such as unit cell dimensions and interatomic distances.« less

  • Magnetic ordering and spin structure in Ca-bearing clinopyroxenes CaM2+(Si, Ge)2O6, M=Fe, Ni, Co, Mn
    Journal of Solid State Chemistry, 2008
    Co-Authors: Günther J. Redhammer, Werner Treutmann, Georg Roth, Werner Paulus, Gilles André, Clemens Pietzonka, Georg Amthauer
    Abstract:

    Abstract The compounds CaFeSi2O6 (Hedenbergite), CaNiGe2O6, CaCoGe2O6 and CaMnGe2O6 have been synthesized by hydrothermal or ceramic sintering techniques and were subsequently characterized by SQUID magnetometry and powder neutneutronfraction in order to determine the magnetic properties and the spin structure at low temperature. All four compounds reveal the well-known clinopyroxene structure-type with monoclinic symmetry, space group C2/c, Z=4 at all temperatures investigated. Below 35 K Hedenbergite shows a ferromagnetic (FM) coupling of spins within the infinite M1 chains of edge-sharing octahedra. This FM coupling dominates an antiferromagnetic (AFM) coupling between neighbouring chains. The magnetic moments lie within the a–c plane and form an angle of 43° with the crystallographic a-axis. Magnetic ordering in CaFeSi2O6 causes significant discontinuities in lattice parameters, Fe–O bond lengths and interatomic Fe–Fe distances through the magnetic phase transition, which could be detected from the Rietveld refinements of powder neutneutronfraction data. CaCoGe2O6 and CaNiGe2O6 show magnetic ordering below 18 K, the spin structures are similar to the one in Hedenbergite with an FM coupling within and an AFM coupling of spins between the M1 chains. The moments lie within the a–c plane. The paramagnetic Curie temperature, however, decreases from CaFeSi2O6 (+40.2 K) to CaCoGe2O6 (+20.1 K) and CaNiGe2O6 (−13.4 K), suggesting an altered interplay between the concurring AFM and FM interaction in and between the M1 chains. CaMnGe2O6 finally shows an AFM ordering below 11 K. Here the magnetic moments are mainly oriented along the a-axis with a small tilt out from the a–c plane.

  • Magnetic ordering and spin structure in Ca-bearing clinopyroxenes CaM2+(Si, Ge)(2)O-6, M = Fe, Ni, Co, Mn
    Journal of Solid State Chemistry, 2008
    Co-Authors: Günther J. Redhammer, Werner Treutmann, Georg Roth, Werner Paulus, Gilles André, Clemens Pietzonka, Georg Amthauer
    Abstract:

    The compounds CaFeSi2O6 (Hedenbergite), CaNiGe2O6, CaCoGe2O6 and CaMnGe2O6 have been synthesized by hydrothermal or ceramic sintering techniques and were Subsequently characterized by SQUID magnetometry and powder neutneutronfraction in order to determine the magnetic properties and the spin structure at low temperature. All four compounds reveal the well-known clinopyroxene structure-type with monoclinic symmetry, space group C2/c, Z = 4 at all temperatures investigated. Below 35 K Hedenbergite shows a ferromagnetic (FM) coupling of spins within the infinite MI chains of edge-sharing octahedra. This FM coupling dominates an antiferromagnetic (AFM) coupling between neighbouring chains. The magnetic moments lie within the a-c plane and form an angle of 43 degrees with the crystallographic a-axis. Magnetic ordering in CaFeSi2O6 causes significant discontinuities in lattice parameters, Fe-O bond lengths and interatomic Fe-Fe distances through the magnetic phase transition, which could be detected from the Rietveld refinements of powder neutneutronfraction data. CaCoGe2O6 and CaNiGe2O6 show magnetic ordering below 18 K, the spin structures are similar to the one in Hedenbergite with an FM Coupling within and an AFM coupling of spins between the MI chains. The moments lie within the a-c plane. The paramagnetic Curie temperature, however, decreases from CaFeSi2O6, (+40.2 K) to CaCoGe2O6 (+20.1 K) and CaNiGe2O6 (-13.4 K), suggesting an altered interplay between the concurring AFM and FM interaction in and between the MI chains. CaMnGe2O6 finally shows an AFM ordering below 11 K. Here the magnetic moments are mainly oriented along the a-axis with a small tilt out from the a-c plane.

Christian Liebske – One of the best experts on this subject based on the ideXlab platform.

  • Thermal expansion along the NaAlSi_2O_6–NaFe^3+Si_2O_6 and NaAlSi_2O_6–CaFe^2+Si_2O_6 solid solutions
    Physics and Chemistry of Minerals, 2008
    Co-Authors: Mario Tribaudino, Fabrizio Nestola, Marco Bruno, Tiziana Boffa Ballaran, Christian Liebske
    Abstract:

    The high temperature volume and axial parameters for six C 2/ c clinopyroxenes along the NaAlSi_2O_6–NaFe^3+Si_2O_6 and NaAlSi_2O_6–CaFe^2+Si_2O_6 joins were determined from room T up to 800°C, using integrated diffraction profiles from in situ high temperature single crystal data collections. The thermal expansion coefficient was determined by fitting the experimental data according to the relation: ln( V / V _0) = α( T  −  T _0). The thermal expansion coefficient increases by about 15% along the jadeiteHedenbergite join, whereas it is almost constant between jadeite and aegirine. The increase is related to the Ca for Na substitution into the M2 site; the same behaviour was observed along the jadeite–diopside solid solution, which presents the same substitution at the M2 site. Strain tensor analysis shows that the major deformation with temperature occurs in all samples along the b axis; on the (010) plane the higher deformation occurs in jadeite and aegirine at a direction almost normal to the tetrahedral–octahedral planes, and in Hedenbergite along the projection of the longer M2–O bonds. The orientation of the strain ellipsoid with temperature in Hedenbergite is close to that observed with pressure in pyroxenes. Along the jadeiteaegirine join instead the high-temperature and high-pressure strain are differently oriented.

  • Thermal expansion along the NaAlSi2O6-NaFe3+Si2O6 and NaAlSi2O6-CaFe2+Si2O6 solid solutions
    Physics and Chemistry of Minerals, 2008
    Co-Authors: Mario Tribaudino, Fabrizio Nestola, Marco Bruno, Tiziana Boffa Ballaran, Christian Liebske
    Abstract:

    The high temperature volume and axial parameters for six C2/c clinopyroxenes along the NaAlSi2O6–NaFe3+Si2O6 and NaAlSi2O6–CaFe2+Si2O6 joins were determined from room T up to 800°C, using integrated diffraction profiles from in situ high temperature single crystal data collections. The thermal expansion coefficient was determined by fitting the experimental data according to the relation: ln(V/V 0) = α(T − T 0). The thermal expansion coefficient increases by about 15% along the jadeiteHedenbergite join, whereas it is almost constant between jadeite and aegirine. The increase is related to the Ca for Na substitution into the M2 site; the same behaviour was observed along the jadeite–diopside solid solution, which presents the same substitution at the M2 site. Strain tensor analysis shows that the major deformation with temperature occurs in all samples along the b axis; on the (010) plane the higher deformation occurs in jadeite and aegirine at a direction almost normal to the tetrahedral–octahedral planes, and in Hedenbergite along the projection of the longer M2–O bonds. The orientation of the strain ellipsoid with temperature in Hedenbergite is close to that observed with pressure in pyroxenes. Along the jadeiteaegirine join instead the high-temperature and high-pressure strain are differently oriented.

  • The crystal structure of pyroxenes along the jadeite–Hedenbergite and jadeite–aegirine joins
    American Mineralogist, 2007
    Co-Authors: Fabrizio Nestola, Mario Tribaudino, Christian Liebske, Tiziana Boffa Ballaran, Marco Bruno
    Abstract:

    The crystal-structures of seven synthetic pyroxenes along the jadeiteHedenbergite (Jd57Hd43, Jd26Hd74, JdHd100) and jadeiteaegirine (Jd100Ae, Jd76Ae24, Jd35Ae65, JdAe100) joins were refined using data collected by means of single-crystal X-ray diffraction (space group C 2/ c , R 4σ between 2.2 and 3.4%). The M2 and M1 polyhedral volumes and bond lengths increase with increasing aegirine and heden-bergite content, moreover the Ca for Na substitution along the jadeiteHedenbergite join changes the M2 coordination from 6 + 2 to 4 + 4, with remarkable tilting of the tetrahedral chains. The value of the displacement parameters follows the trend U eqM2 > U eqO2 > U eqO3 > U eqO1 > U eqM1 ≈ U eqT for all samples belonging to the jadeiteaegirine join and for pure Hedenbergite; in contrast,, for pyroxenes with intermediate compositions between Hedenbergite and jadeite the trend is U eqO1 > U eqO2 > U eqM2 > U eqO3 > U eqM1 ≈ U eqT, with O1 and O2 having anomalously large displacement parameters, probably due to different local structural configuration around the cations with different size and charge. Cation substitution at the M1 site of Na-pyroxenes gives rise to a different structural deformation with respect of the double substitution at both the M1 and M2 sites in (Na,Ca)(M3+,M2+)Si2O6 pyroxenes as the rigid tetrahedral chains try to accommodate both the increasing size of the M1 site and the different coordination requirement of the M2 site.

Marco Bruno – One of the best experts on this subject based on the ideXlab platform.

  • Thermal expansion along the NaAlSi_2O_6–NaFe^3+Si_2O_6 and NaAlSi_2O_6–CaFe^2+Si_2O_6 solid solutions
    Physics and Chemistry of Minerals, 2008
    Co-Authors: Mario Tribaudino, Fabrizio Nestola, Marco Bruno, Tiziana Boffa Ballaran, Christian Liebske
    Abstract:

    The high temperature volume and axial parameters for six C 2/ c clinopyroxenes along the NaAlSi_2O_6–NaFe^3+Si_2O_6 and NaAlSi_2O_6–CaFe^2+Si_2O_6 joins were determined from room T up to 800°C, using integrated diffraction profiles from in situ high temperature single crystal data collections. The thermal expansion coefficient was determined by fitting the experimental data according to the relation: ln( V / V _0) = α( T  −  T _0). The thermal expansion coefficient increases by about 15% along the jadeite–Hedenbergite join, whereas it is almost constant between jadeite and aegirine. The increase is related to the Ca for Na substitution into the M2 site; the same behaviour was observed along the jadeite–diopside solid solution, which presents the same substitution at the M2 site. Strain tensor analysis shows that the major deformation with temperature occurs in all samples along the b axis; on the (010) plane the higher deformation occurs in jadeite and aegirine at a direction almost normal to the tetrahedral–octahedral planes, and in Hedenbergite along the projection of the longer M2–O bonds. The orientation of the strain ellipsoid with temperature in Hedenbergite is close to that observed with pressure in pyroxenes. Along the jadeite–aegirine join instead the high-temperature and high-pressure strain are differently oriented.

  • Thermal expansion along the NaAlSi2O6-NaFe3+Si2O6 and NaAlSi2O6-CaFe2+Si2O6 solid solutions
    Physics and Chemistry of Minerals, 2008
    Co-Authors: Mario Tribaudino, Fabrizio Nestola, Marco Bruno, Tiziana Boffa Ballaran, Christian Liebske
    Abstract:

    The high temperature volume and axial parameters for six C2/c clinopyroxenes along the NaAlSi2O6–NaFe3+Si2O6 and NaAlSi2O6–CaFe2+Si2O6 joins were determined from room T up to 800°C, using integrated diffraction profiles from in situ high temperature single crystal data collections. The thermal expansion coefficient was determined by fitting the experimental data according to the relation: ln(V/V 0) = α(T − T 0). The thermal expansion coefficient increases by about 15% along the jadeite–Hedenbergite join, whereas it is almost constant between jadeite and aegirine. The increase is related to the Ca for Na substitution into the M2 site; the same behaviour was observed along the jadeite–diopside solid solution, which presents the same substitution at the M2 site. Strain tensor analysis shows that the major deformation with temperature occurs in all samples along the b axis; on the (010) plane the higher deformation occurs in jadeite and aegirine at a direction almost normal to the tetrahedral–octahedral planes, and in Hedenbergite along the projection of the longer M2–O bonds. The orientation of the strain ellipsoid with temperature in Hedenbergite is close to that observed with pressure in pyroxenes. Along the jadeite–aegirine join instead the high-temperature and high-pressure strain are differently oriented.

  • The crystal structure of pyroxenes along the jadeite–Hedenbergite and jadeite–aegirine joins
    American Mineralogist, 2007
    Co-Authors: Fabrizio Nestola, Mario Tribaudino, Christian Liebske, Tiziana Boffa Ballaran, Marco Bruno
    Abstract:

    The crystal-structures of seven synthetic pyroxenes along the jadeite–Hedenbergite (Jd57Hd43, Jd26Hd74, JdHd100) and jadeite–aegirine (Jd100Ae, Jd76Ae24, Jd35Ae65, JdAe100) joins were refined using data collected by means of single-crystal X-ray diffraction (space group C 2/ c , R 4σ between 2.2 and 3.4%). The M2 and M1 polyhedral volumes and bond lengths increase with increasing aegirine and heden-bergite content, moreover the Ca for Na substitution along the jadeite–Hedenbergite join changes the M2 coordination from 6 + 2 to 4 + 4, with remarkable tilting of the tetrahedral chains. The value of the displacement parameters follows the trend U eqM2 > U eqO2 > U eqO3 > U eqO1 > U eqM1 ≈ U eqT for all samples belonging to the jadeite–aegirine join and for pure Hedenbergite; in contrast,, for pyroxenes with intermediate compositions between Hedenbergite and jadeite the trend is U eqO1 > U eqO2 > U eqM2 > U eqO3 > U eqM1 ≈ U eqT, with O1 and O2 having anomalously large displacement parameters, probably due to different local structural configuration around the cations with different size and charge. Cation substitution at the M1 site of Na-pyroxenes gives rise to a different structural deformation with respect of the double substitution at both the M1 and M2 sites in (Na,Ca)(M3+,M2+)Si2O6 pyroxenes as the rigid tetrahedral chains try to accommodate both the increasing size of the M1 site and the different coordination requirement of the M2 site.

Li Zhang – One of the best experts on this subject based on the ideXlab platform.

  • 57 Fe nuclear forward scattering of synchrotron radiation in Hedenbergite CaFeSi 2 O 6 at hydrostatic pressures up to 68 GPa
    American Mineralogist, 1999
    Co-Authors: Li Zhang, H. Ahsbahs, S. S. Hafner, J. Stanek, H. F. Gruensteudel, J. Metge, R. Rueffer
    Abstract:

    The 57 Fe nuclear forward scattering (NFS) of synchrotron radiation and the use of diamond anvils with helium as pressure medium allowed study of the electronic state of Fe (super 2+) in the chain silicate Hedenbergite CaFeSi 2 O 6 at pressures up to 68 GPa. Characteristics of NFS time spectra were compared with those of conventional Mossbauer spectra. NFS time spectra of 57 Fe in Hedenbergite revealed a reversible phase transition between 53 and 68 GPa at room temperature, which is probably a transition from the paramagnetic phase at low pressures to a magnetic phase at high pressures. If this interpretation is correct, the Neel temptemperature T N of Hedenbergite depends critically on pressure (T N = 45 K at 1 atm).

  • Single-crystal compression and crystal structure of clinopyroxene up to 10 GPa
    American Mineralogist, 1997
    Co-Authors: Li Zhang, H. Ahsbahs, S. S. Hafner, Ali Kutoglu
    Abstract:

    The hydrostatic compression of synthetic single crystals of diopside, CaMgSi 2O6, and Hedenbergite, CaFeSi2O6, was studied at 33 pressures up to 10 GPa by X-ray diffraction. In addition, intensity data for Hedenbergite were collected at 12 pressures up to 10 GPa. For determination of the elasticity two crystals were loaded together in a diamond cell. The axial compressibilities ba, bb, and bc of diopside and Hedenbergite are 2.36(4), 3.17(4), and 2.50(4) 3 10 23 GPa 21 , and 1.93(5), 3.38(6), and 2.42(8) 3 10 23 GPa 21 , respectively. The bulk moduli ( ) and their pressure derivatives ( ) were determined simultaneously KK

Günther J. Redhammer – One of the best experts on this subject based on the ideXlab platform.

  • Electronic and magnetic structure of pyroxenes I. Hedenbergite
    Physics and Chemistry of Minerals, 2009
    Co-Authors: Michael Grodzicki, Günther J. Redhammer, M. Reissner, W. Steiner, G. Amthauer
    Abstract:

    The electronic and magnetic structure of the chain silicate Hedenbergite (CaFe^2+Si_2O_6) has been investigated by a number of experimental methods (neutron diffraction, Mössbauer spectroscopy, low temperature magnetic measurements), as well as by electronic structure calculations for clusters of different size in the local spin density approximation. The calculated size-converged spectroscopic data ( d – d excitation energies, hyperfine parameters) are in quantitative agreement with the respective experimental values. The calculated magnetic coupling constants are about +25 cm^−1 and −4 cm^−1 for intra-chain and inter-chain coupling, respectively. The latter value shows that weak superexchange via edges of silicon tetrahedra is well reproduced by the calculations, and it is in qualitative agreement with an observed metamagnetic transition at 4.2 K in an external magnetic field with an onset around 4 T but saturation is not achieved in fields up to 14.5 T. The large ferromagnetic intra-chain coupling is attributed to a nearly degenerate ground state. The ratio between the two magnetic coupling constants agrees with earlier estimates on similar compounds. Finally, it is demonstrated how the detailed discussion of the various exchange pathways contributes to an improved understanding of the connection between magnetic properties and the geometrical structure.

  • magnetic ordering and spin structure in ca bearing clinopyroxenes cam2 si ge 2o6 m fe ni co mn
    Journal of Solid State Chemistry, 2008
    Co-Authors: Günther J. Redhammer, Werner Treutmann, Georg Roth, Werner Paulus, Gilles André, Clemens Pietzonka, Georg Amthauer
    Abstract:

    The compounds CaFeSi{sub 2}O{sub 6} (Hedenbergite), CaNiGe{sub 2}O{sub 6}, CaCoGe{sub 2}O{sub 6} and CaMnGe{sub 2}O{sub 6} have been synthesized by hydrothermal or ceramic sintering techniques and were subsequently characterized by SQUID magnetometry and powder neutron diffraction in order to determine the magnetic properties and the spin structure at low temperature. All four compounds reveal the well-known clinopyroxene structure-type with monoclinic symmetry, space group C2/c, Z=4 at all temperatures investigated. Below 35 K Hedenbergite shows a ferromagnetic (FM) coupling of spins within the infinite M1 chains of edge-sharing octahedra. This FM coupling dominates an antiferromagnetic (AFM) coupling between neighbouring chains. The magnetic moments lie within the a-c plane and form an angle of 43 deg. with the crystallographic a-axis. Magnetic ordering in CaFeSi{sub 2}O{sub 6} causes significant discontinuities in lattice parameters, Fe-O bond lengths and interatomic Fe-Fe distances through the magnetic phase transition, which could be detected from the Rietveld refinements of powder neutron diffraction data. CaCoGe{sub 2}O{sub 6} and CaNiGe{sub 2}O{sub 6} show magnetic ordering below 18 K, the spin structures are similar to the one in Hedenbergite with an FM coupling within and an AFM coupling of spins between the M1 chains. The moments lie within the a-c plane.more » The paramagnetic Curie temperature, however, decreases from CaFeSi{sub 2}O{sub 6} (+40.2 K) to CaCoGe{sub 2}O{sub 6} (+20.1 K) and CaNiGe{sub 2}O{sub 6} (-13.4 K), suggesting an altered interplay between the concurring AFM and FM interaction in and between the M1 chains. CaMnGe{sub 2}O{sub 6} finally shows an AFM ordering below 11 K. Here the magnetic moments are mainly oriented along the a-axis with a small tilt out from the a-c plane. – Graphical abstract: The magnetic properties and magnetic spins structures of 4 members of the clinopyroxenes are determined from susceptibility measurements and neutron diffraction. The magnetic ordering is accompanied by distinct alterations in structural parameters such as unit cell dimensions and interatomic distances.« less

  • Magnetic ordering and spin structure in Ca-bearing clinopyroxenes CaM2+(Si, Ge)2O6, M=Fe, Ni, Co, Mn
    Journal of Solid State Chemistry, 2008
    Co-Authors: Günther J. Redhammer, Werner Treutmann, Georg Roth, Werner Paulus, Gilles André, Clemens Pietzonka, Georg Amthauer
    Abstract:

    Abstract The compounds CaFeSi2O6 (Hedenbergite), CaNiGe2O6, CaCoGe2O6 and CaMnGe2O6 have been synthesized by hydrothermal or ceramic sintering techniques and were subsequently characterized by SQUID magnetometry and powder neutron diffraction in order to determine the magnetic properties and the spin structure at low temperature. All four compounds reveal the well-known clinopyroxene structure-type with monoclinic symmetry, space group C2/c, Z=4 at all temperatures investigated. Below 35 K Hedenbergite shows a ferromagnetic (FM) coupling of spins within the infinite M1 chains of edge-sharing octahedra. This FM coupling dominates an antiferromagnetic (AFM) coupling between neighbouring chains. The magnetic moments lie within the a–c plane and form an angle of 43° with the crystallographic a-axis. Magnetic ordering in CaFeSi2O6 causes significant discontinuities in lattice parameters, Fe–O bond lengths and interatomic Fe–Fe distances through the magnetic phase transition, which could be detected from the Rietveld refinements of powder neutron diffraction data. CaCoGe2O6 and CaNiGe2O6 show magnetic ordering below 18 K, the spin structures are similar to the one in Hedenbergite with an FM coupling within and an AFM coupling of spins between the M1 chains. The moments lie within the a–c plane. The paramagnetic Curie temperature, however, decreases from CaFeSi2O6 (+40.2 K) to CaCoGe2O6 (+20.1 K) and CaNiGe2O6 (−13.4 K), suggesting an altered interplay between the concurring AFM and FM interaction in and between the M1 chains. CaMnGe2O6 finally shows an AFM ordering below 11 K. Here the magnetic moments are mainly oriented along the a-axis with a small tilt out from the a–c plane.