Preparation et caracterisation des ferrites de calcium CaFe2+nO4+n a valeurs fractionnaires de n (, ) et leur incidence sur le diagramme Fe-Ca-O A 1120°C

Malaman, B.; Alebouyeh, H.; Jeannot, F.; Courtois, A.; Gerardin, R.; Evrard, O.

doi:10.1016/0025-5408(81)90290-7

Cited by 24 publications

(3 citation statements)

References 6 publications

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“…These compounds consist of CaTi 2 O 4 -type CaFe 2 O 4 slabs, separated by rock salt-type FeO slabs of a thickness that increases with increasing n . n is known to take integer values of 1, 2 and 3 4 , and half-integer mean values of 1.5 and 2.5 are found when there are alternating (FeO) n and (FeO) n +1 blocks 5 . The n = 3 member of the series, CaFe 5 O 7 , exhibits a complex structure 6 , stacking faults that are synthesis dependent 7,8 , complex long range magnetic order and Charge Order (CO), an important phenomenon in mixed-valent compounds 9 .…”

Section: Introductionmentioning

confidence: 99%

Single phase charge ordered stoichiometric CaFe3O5 with commensurate and incommensurate trimeron ordering

et al. 2019

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Mixed-valent transition metal compounds display complex structural, electronic and magnetic properties which can often be exquisitely tuned. Here the charge-ordered state of stoichiometric CaFe3O5 is probed using neutron powder diffraction, Monte Carlo simulation and symmetry analysis. Magnetic ordering is dominated by the formation of ferromagnetic Fe3+–Fe2+–Fe3+ trimers which are evident above the magnetic ordering transition. Between TN = 289 K and 281 K an incommensurate magnetically ordered phase develops due to magnetic frustration, but a spin Jahn-Teller distortion lifts the frustration and enables the magnetic ordering to lock in to a charge-ordered commensurate state at lower temperatures. Stoichiometric CaFe3O5 exhibits single phase behaviour throughout and avoids the phase separation into two distinct crystallographic phases with different magnetic structures and Fe valence distributions reported recently, which likely occurs due to partial Fe2+ for Ca2+ substitution. This underlines the sensitivity of the magnetism and chemistry of these mixed-valent systems to composition.

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Section: Introductionmentioning

confidence: 99%

Single phase charge ordered stoichiometric CaFe3O5 with commensurate and incommensurate trimeron ordering

et al. 2019

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“…Within this family, the compounds with n = 0, 1, 3/2, 2, 5/2, and 3 have been reported. 29,30 Interestingly, for n = 1/4, the compound Ca 4 Fe 9 O 17 crystallizes in a different structure (S.G. C2, no. 5), built up by layers of Fe atoms in edge-sharing FeO 6 octahedra and vertex-sharing Fe in trigonal-based bipyramid coordination (see Fig.…”

Section: Introductionmentioning

confidence: 99%

Appraisal of calcium ferrites as cathodes for calcium rechargeable batteries: DFT, synthesis, characterization and electrochemistry of Ca₄Fe₉O₁₇

et al. 2020

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“…Here n is not necessarily an integer, but compounds with fractional n have also been reported [70]. The result is a large family of complex oxides where F e is present in two oxidation states: 2+ in the F eO block and 3+ in the CaF e 2 O 4 unit [71,72].…”

Section: Modulated Phasesmentioning

confidence: 99%

Modulated phases of ferroic oxides

Damerio¹

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Samenvatting AcknowledgmentsCurriculum vitae viii Contents Materials in which competing interactions lead to the appearance of modulated phases are not only fascinating from a fundamental point of view, but are also promising candidates for applications. In particular, at the transition point between different periodicities, chaotic behaviour and large fluctuations are expected, that can be exploited as deliberate means to enhance electronic adaptability. Even though the concept of "edge of chaos" [20, 21] is well developed in dynamical systems, described by periodicity doubling cascades and bifurcation theory, and it is often linked to self-adaptation and learning in complex systems [22], its use in relation to enhanced electronic functionalities is under-explored [23]. Because an analogy has been made between chaos and the existence of modulated phases in systems with competing interactions, these could be employed with the goal of creating highly adaptable systems at "the edge of (spatial) chaos" [24]. This thesis focuses on the materials science aspects around developing this type of adaptability and can be considered as a first step in this direction.To do so, understanding and possibly control on the relative stability of the competing structures is needed. Therefore, for this research, we have selected two examples of solid state systems, CaF e 2 O 4 and BaT iO 3 , displaying multiple periodic structures that can be accessed in the laboratory. The modulation in CaF e 2 O 4 arises from the alternation of chains of parallel spins in two overall antiferromagnetic structures. In BaT iO 3 the modulation is given by periodic ferroelastic domains with alternating polarization direction. In both cases, growing the material in thin film form on a crystalline substrate allows to exploit epitaxial strain as a handle to tune the relative stability of the different phases. In the case of CaF e 2 O 4 , which is the main 1.1.1 CaFe 2 O 4 Unlike many the other compounds with the unit formula AM 2 O 4 , CaF e 2 O 4 does not have the Spinel structure [49] and, instead, crystallizes in a orthorhombic structure with space group P nma and lattice parameters a = 9.230 Å , b = 3.024 Å and c = 10.705 Å, that was first characterized in the late 1950s [50-52]. The F e 3+ ions of the CaF e 2 O 4 structure occupy two crystallographically distinct positions, F e(1) and F e(2), each surrounded by 6 oxygen atoms in octahedral coordination. Both F e types forms zig-zag chains that run parallel to the b-axis. F eO 6 octahedra within the same chain share edges, whereas neighbouring chains are connected through corners. This connectivity results into a tunnel structure with the Ca 2+ cations occupying bicapped triangular prismatic cavities with oxygen coordination number of 8. The same characteristic M O 6 octahedra network is also found in several other compounds, including CaCr 2 O 4 , CaV 2 O 4 , CaM n 2 O 4 , CaT i 2 O 4 1 and Eu 3 O 4 , [53] as well as many rare-earth oxides with large alkali cations, that are sometimes referred to as...

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Preparation et caracterisation des ferrites de calcium CaFe2+nO4+n a valeurs fractionnaires de n (, ) et leur incidence sur le diagramme Fe-Ca-O A 1120°C

Cited by 24 publications

References 6 publications

Single phase charge ordered stoichiometric CaFe3O5 with commensurate and incommensurate trimeron ordering

Single phase charge ordered stoichiometric CaFe3O5 with commensurate and incommensurate trimeron ordering

Appraisal of calcium ferrites as cathodes for calcium rechargeable batteries: DFT, synthesis, characterization and electrochemistry of Ca₄Fe₉O₁₇

Modulated phases of ferroic oxides

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Preparation et caracterisation des ferrites de calcium CaFe2+nO4+n a valeurs fractionnaires de n (, ) et leur incidence sur le diagramme Fe-Ca-O A 1120°C

Cited by 24 publications

References 6 publications

Single phase charge ordered stoichiometric CaFe3O5 with commensurate and incommensurate trimeron ordering

Single phase charge ordered stoichiometric CaFe3O5 with commensurate and incommensurate trimeron ordering

Appraisal of calcium ferrites as cathodes for calcium rechargeable batteries: DFT, synthesis, characterization and electrochemistry of Ca4Fe9O17

Modulated phases of ferroic oxides

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Appraisal of calcium ferrites as cathodes for calcium rechargeable batteries: DFT, synthesis, characterization and electrochemistry of Ca₄Fe₉O₁₇