32 research outputs found
Canted antiferromagnetism in high purity prepared by a novel wet-chemical synthesis method
We report a novel synthesis method for, and structural and magnetic
characterization of the fluoroperovskite . We have developed
a wet-chemical method that allows preparation of large volumes of air-sensitive
fluoroperovskites with high purity. has a N\'eel temperature
() of 90 K and a Weiss constant () of -124 K, corresponding to
dominant antiferromagnetic interactions. Below , a slight difference is
observed between zero-field and field cooled samples, indicating spin-canting
and weak ferromagnetism. AC magnetometry confirms that weak ferromagnetism is
inherent to and not due to impurities. From powder neutron
diffraction data, we describe the magnetic structure precisely as a weakly
canted G-type (magnetic space group ). A ferromagnetic component is
allowed in , however, this component may be absent in zero magnetic
fields and is too small to be confirmed on the basis of powder neutron
diffraction data.Comment: 9 pages, 10 figure
Influence des ions sulfates sur la physico-chimie d'oxydes de fer type perovskite
In this study, we have shown that in perovskite-type iron oxides, sulfate ions (SO42-) can be used to bring structural and electronic anisotropy, or on the contrary to break long distance ordering and cause the isotropy of the material.Thus, this work made it possible to isolate the two-dimensional compounds: Sr4Fe2.5-xâĄx07.25-(3x/2)(SO4)0.5 (with x = 0.25 and 0.5). They can be described as an intergrowth SrO/SrFeO2,5/SrFe0,5-xâĄxO1,25-(3x/2)(SO4)0.5/SrFeO2,5 and crystallize in a quadratic mean cell I4/mmm (a=ap et câ29 Ă
). The unbridged sulfates tetrahedra are oriented transversely with respect to c â for x=0.5 and longitudinal for x=0 and 0.25 because bridged to the iron pyramids of the shared layer. The iron atoms of the non-mixed layers SrFeO2,5 are in pyramidal coordination for x=0 and pyramidal and octahedral coordination for x=0.5 and x=0.25, in order to respect the trivalence of iron. However, for x=0.5, two magnetic configurations are observed whereas the compounds x=0 and x=0.25 show only one. In the compound Sr4Fe2.5âĄxO7.25(SO4)0.25(CO3)0.25, the influence of the carbonates (CO32-) is directly felt on the stacking parameter, which is smaller. The compounds are semiconductors with high electronic resistivity values (of the order of 106Ω.cm) and are not ionic conductors.The ordered phase "15R" SrFe0.6Cr0.4O2.8 becomes disordered when 10% of the iron is substituted with sulfates (SrFe0.5Cr0.4O2.1(SO4)0.1) and adopts a pseudo-cubic structure. Its physical properties are then modified because we switch from a ferromagnetic to an antiferromagnetic behavior (TN=800K). This oxygen-deficient compound shows more or less large structural defects and a semiconductor behavior. No ionic conduction phenomenon is observed.Au cours de cette Ă©tude, nous avons montrĂ© que dans les oxydes de fer type perovskite, les ions sulfates (SO42-) pouvaient ĂȘtre utilisĂ©s Ă escient pour apporter de l'anisotropie cristalline et Ă©lectronique ou bien au contraire pour casser les mises en ordre Ă longue distance et provoquer l'isotropie du matĂ©riau. Ainsi, ce travail a permis d'isoler les composĂ©s bidimensionnels : Sr4Fe2.5-xâĄxO7.25-(3x/2)(SO4)0.5 (avec x=0, 0.25 et 0.5). Ils peuvent ĂȘtre dĂ©crits comme une intercroissance SrO/SrFeO2,5/SrFe0,5-xâĄxO1,25-(3x/2)(SO4)0,5/SrFeO2,5 et cristallisent dans une maille moyenne quadratique I4/mmm (a=ap et câ29 Ă
). Les tĂ©traĂšdres de sulfates non-pontĂ©s se prĂ©sentent de façon transversale par rapport Ă c â pour x=0,5 et longitudinale pour x=0 et 0,25 parce que pontĂ©s aux pyramides de fer de la couche partagĂ©e. Les atomes de fer des couches non-mixtes SrFeO2,5 se situent eux en coordinence pyramidale pour x=0 et pyramidale et octaĂ©drique pour x=0.5 et x=0.25 afin de respecter la trivalence du fer. Quel que soit x, les composĂ©s sont antiferromagnĂ©tiques de type G (les spins se situant dans le plan (a,b)). Cependant, pour x=0,5, deux configurations magnĂ©tiques sont observĂ©es, tandis que les composĂ©s x=0 et x=0.25 n'en montrent qu'une seule. Dans le composĂ© Sr4Fe2.5âĄxO7.25(SO4)0.25(CO3)0.25, l'influence des carbonates (CO32-) se ressent directement sur le paramĂštre d'empilement, qui est plus petit. Cela n'entraĂźne cependant aucun changement sensible dans les propriĂ©tĂ©s physiques. Les composĂ©s sont des semi-conducteurs prĂ©sentant de fortes valeurs de rĂ©sistivitĂ© Ă©lectronique (de l'ordre de 106Ω.cm) et ne sont pas conducteurs ioniques.La phase ordonnĂ©e "15R" SrFe0.6Cr0.4O2.8 se dĂ©sordonne lorsque l'on substitue 10% du fer par des sulfates (SrFe0.5Cr0.4O2.1(SO4)0.1) et adopte une structure pseudo-cubique. Ses propriĂ©tĂ©s physiques sont alors bouleversĂ©es puisque l'on passe d'un comportement ferromagnĂ©tique Ă antiferromagnĂ©tique (TN=800K). Ce composĂ© trĂšs lacunaire en oxygĂšne montre des dĂ©fauts structuraux plus ou moins Ă©tendus et un comportement de type semi-conducteur. Aucun phĂ©nomĂšne de conduction ionique n'est observĂ©
Influence of sulfates ions on the physical and chemical properties of perovskite type iron oxides
Au cours de cette Ă©tude, nous avons montrĂ© que dans les oxydes de fer type perovskite, les ions sulfates (SO42-) pouvaient ĂȘtre utilisĂ©s Ă escient pour apporter de l'anisotropie cristalline et Ă©lectronique ou bien au contraire pour casser les mises en ordre Ă longue distance et provoquer l'isotropie du matĂ©riau. Ainsi, ce travail a permis d'isoler les composĂ©s bidimensionnels : Sr4Fe2.5-xâĄxO7.25-(3x/2)(SO4)0.5 (avec x=0, 0.25 et 0.5). Ils peuvent ĂȘtre dĂ©crits comme une intercroissance SrO/SrFeO2,5/SrFe0,5-xâĄxO1,25-(3x/2)(SO4)0,5/SrFeO2,5 et cristallisent dans une maille moyenne quadratique I4/mmm (a=ap et câ29 Ă
). Les tĂ©traĂšdres de sulfates non-pontĂ©s se prĂ©sentent de façon transversale par rapport Ă c â pour x=0,5 et longitudinale pour x=0 et 0,25 parce que pontĂ©s aux pyramides de fer de la couche partagĂ©e. Les atomes de fer des couches non-mixtes SrFeO2,5 se situent eux en coordinence pyramidale pour x=0 et pyramidale et octaĂ©drique pour x=0.5 et x=0.25 afin de respecter la trivalence du fer. Quel que soit x, les composĂ©s sont antiferromagnĂ©tiques de type G (les spins se situant dans le plan (a,b)). Cependant, pour x=0,5, deux configurations magnĂ©tiques sont observĂ©es, tandis que les composĂ©s x=0 et x=0.25 n'en montrent qu'une seule. Dans le composĂ© Sr4Fe2.5âĄxO7.25(SO4)0.25(CO3)0.25, l'influence des carbonates (CO32-) se ressent directement sur le paramĂštre d'empilement, qui est plus petit. Cela n'entraĂźne cependant aucun changement sensible dans les propriĂ©tĂ©s physiques. Les composĂ©s sont des semi-conducteurs prĂ©sentant de fortes valeurs de rĂ©sistivitĂ© Ă©lectronique (de l'ordre de 106Ω.cm) et ne sont pas conducteurs ioniques.La phase ordonnĂ©e "15R" SrFe0.6Cr0.4O2.8 se dĂ©sordonne lorsque l'on substitue 10% du fer par des sulfates (SrFe0.5Cr0.4O2.1(SO4)0.1) et adopte une structure pseudo-cubique. Ses propriĂ©tĂ©s physiques sont alors bouleversĂ©es puisque l'on passe d'un comportement ferromagnĂ©tique Ă antiferromagnĂ©tique (TN=800K). Ce composĂ© trĂšs lacunaire en oxygĂšne montre des dĂ©fauts structuraux plus ou moins Ă©tendus et un comportement de type semi-conducteur. Aucun phĂ©nomĂšne de conduction ionique n'est observĂ©.In this study, we have shown that in perovskite-type iron oxides, sulfate ions (SO42-) can be used to bring structural and electronic anisotropy, or on the contrary to break long distance ordering and cause the isotropy of the material.Thus, this work made it possible to isolate the two-dimensional compounds: Sr4Fe2.5-xâĄx07.25-(3x/2)(SO4)0.5 (with x = 0.25 and 0.5). They can be described as an intergrowth SrO/SrFeO2,5/SrFe0,5-xâĄxO1,25-(3x/2)(SO4)0.5/SrFeO2,5 and crystallize in a quadratic mean cell I4/mmm (a=ap et câ29 Ă
). The unbridged sulfates tetrahedra are oriented transversely with respect to c â for x=0.5 and longitudinal for x=0 and 0.25 because bridged to the iron pyramids of the shared layer. The iron atoms of the non-mixed layers SrFeO2,5 are in pyramidal coordination for x=0 and pyramidal and octahedral coordination for x=0.5 and x=0.25, in order to respect the trivalence of iron. However, for x=0.5, two magnetic configurations are observed whereas the compounds x=0 and x=0.25 show only one. In the compound Sr4Fe2.5âĄxO7.25(SO4)0.25(CO3)0.25, the influence of the carbonates (CO32-) is directly felt on the stacking parameter, which is smaller. The compounds are semiconductors with high electronic resistivity values (of the order of 106Ω.cm) and are not ionic conductors.The ordered phase "15R" SrFe0.6Cr0.4O2.8 becomes disordered when 10% of the iron is substituted with sulfates (SrFe0.5Cr0.4O2.1(SO4)0.1) and adopts a pseudo-cubic structure. Its physical properties are then modified because we switch from a ferromagnetic to an antiferromagnetic behavior (TN=800K). This oxygen-deficient compound shows more or less large structural defects and a semiconductor behavior. No ionic conduction phenomenon is observed
Influence des ions sulfates sur la physico-chimie d'oxydes de fer type perovskite
In this study, we have shown that in perovskite-type iron oxides, sulfate ions (SO42-) can be used to bring structural and electronic anisotropy, or on the contrary to break long distance ordering and cause the isotropy of the material.Thus, this work made it possible to isolate the two-dimensional compounds: Sr4Fe2.5-xâĄx07.25-(3x/2)(SO4)0.5 (with x = 0.25 and 0.5). They can be described as an intergrowth SrO/SrFeO2,5/SrFe0,5-xâĄxO1,25-(3x/2)(SO4)0.5/SrFeO2,5 and crystallize in a quadratic mean cell I4/mmm (a=ap et câ29 Ă
). The unbridged sulfates tetrahedra are oriented transversely with respect to c â for x=0.5 and longitudinal for x=0 and 0.25 because bridged to the iron pyramids of the shared layer. The iron atoms of the non-mixed layers SrFeO2,5 are in pyramidal coordination for x=0 and pyramidal and octahedral coordination for x=0.5 and x=0.25, in order to respect the trivalence of iron. However, for x=0.5, two magnetic configurations are observed whereas the compounds x=0 and x=0.25 show only one. In the compound Sr4Fe2.5âĄxO7.25(SO4)0.25(CO3)0.25, the influence of the carbonates (CO32-) is directly felt on the stacking parameter, which is smaller. The compounds are semiconductors with high electronic resistivity values (of the order of 106Ω.cm) and are not ionic conductors.The ordered phase "15R" SrFe0.6Cr0.4O2.8 becomes disordered when 10% of the iron is substituted with sulfates (SrFe0.5Cr0.4O2.1(SO4)0.1) and adopts a pseudo-cubic structure. Its physical properties are then modified because we switch from a ferromagnetic to an antiferromagnetic behavior (TN=800K). This oxygen-deficient compound shows more or less large structural defects and a semiconductor behavior. No ionic conduction phenomenon is observed.Au cours de cette Ă©tude, nous avons montrĂ© que dans les oxydes de fer type perovskite, les ions sulfates (SO42-) pouvaient ĂȘtre utilisĂ©s Ă escient pour apporter de l'anisotropie cristalline et Ă©lectronique ou bien au contraire pour casser les mises en ordre Ă longue distance et provoquer l'isotropie du matĂ©riau. Ainsi, ce travail a permis d'isoler les composĂ©s bidimensionnels : Sr4Fe2.5-xâĄxO7.25-(3x/2)(SO4)0.5 (avec x=0, 0.25 et 0.5). Ils peuvent ĂȘtre dĂ©crits comme une intercroissance SrO/SrFeO2,5/SrFe0,5-xâĄxO1,25-(3x/2)(SO4)0,5/SrFeO2,5 et cristallisent dans une maille moyenne quadratique I4/mmm (a=ap et câ29 Ă
). Les tĂ©traĂšdres de sulfates non-pontĂ©s se prĂ©sentent de façon transversale par rapport Ă c â pour x=0,5 et longitudinale pour x=0 et 0,25 parce que pontĂ©s aux pyramides de fer de la couche partagĂ©e. Les atomes de fer des couches non-mixtes SrFeO2,5 se situent eux en coordinence pyramidale pour x=0 et pyramidale et octaĂ©drique pour x=0.5 et x=0.25 afin de respecter la trivalence du fer. Quel que soit x, les composĂ©s sont antiferromagnĂ©tiques de type G (les spins se situant dans le plan (a,b)). Cependant, pour x=0,5, deux configurations magnĂ©tiques sont observĂ©es, tandis que les composĂ©s x=0 et x=0.25 n'en montrent qu'une seule. Dans le composĂ© Sr4Fe2.5âĄxO7.25(SO4)0.25(CO3)0.25, l'influence des carbonates (CO32-) se ressent directement sur le paramĂštre d'empilement, qui est plus petit. Cela n'entraĂźne cependant aucun changement sensible dans les propriĂ©tĂ©s physiques. Les composĂ©s sont des semi-conducteurs prĂ©sentant de fortes valeurs de rĂ©sistivitĂ© Ă©lectronique (de l'ordre de 106Ω.cm) et ne sont pas conducteurs ioniques.La phase ordonnĂ©e "15R" SrFe0.6Cr0.4O2.8 se dĂ©sordonne lorsque l'on substitue 10% du fer par des sulfates (SrFe0.5Cr0.4O2.1(SO4)0.1) et adopte une structure pseudo-cubique. Ses propriĂ©tĂ©s physiques sont alors bouleversĂ©es puisque l'on passe d'un comportement ferromagnĂ©tique Ă antiferromagnĂ©tique (TN=800K). Ce composĂ© trĂšs lacunaire en oxygĂšne montre des dĂ©fauts structuraux plus ou moins Ă©tendus et un comportement de type semi-conducteur. Aucun phĂ©nomĂšne de conduction ionique n'est observĂ©
Effect of the Niobium Doping Concentration on the Charge Storage Mechanism of Mesoporous Anatase Beads as an Anode for High-Rate Li-Ion Batteries
A promising strategy to improve the rate performance of Li-ion batteries is to enhance and facilitate the insertion of Li ions into nanostructured oxides like TiO2. In this work, we present a systematic study of pentavalent-doped anatase TiO2 materials for third-generation high-rate Li-ion batteries. Mesoporous niobium-doped anatase beads (Nb-doped TiO2) with different Nb5+ doping (n-type) concentrations (0.1, 1.0, and 10% at.) were synthesized via an improved template approach followed by hydrothermal treatment. The formation of intrinsic n-type defects and oxygen vacancies under RT conditions gives rise to a metallic-type conduction due to a shift of the Fermi energy level. The increase in the metallic character, confirmed by electrochemical impedance spectroscopy, enhances the performance of the anatase bead electrodes in terms of rate capability and provides higher capacities both at low and fast charging rates. The experimental data were supported by density functional theory (DFT) calculations showing how a different n-type doping can be correlated to the same electrochemical effect on the final device. The Nb-doped TiO2 electrode materials exhibit an improved cycling stability at all the doping concentrations by overcoming the capacity fade shown in the case of pure TiO2 beads. The 0.1% Nb-doped TiO2-based electrodes exhibit the highest reversible capacities of 180 mAh gâ1 at 1C (330 mA gâ1) after 500 cycles and 110 mAh gâ1 at 10C (3300 mA gâ1) after 1000 cycles. Our experimental and computational results highlight the possibility of using n-type doped TiO2 materials as anodes in high-rate Li-ion batteries
Enhanced magnetic frustration in a new high entropy diamond lattice spinel oxide
International audienceHighâentropy stabilization chemistry offers a new paradigm in the design of functional materials stabilized by the high configurational entropy. In the present work, a new high entropy spinel material with composition (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)Al2O4 is introduced, detailed structural and microstructural characterizations highlight that the material crystallizes in a cubic spinel structure with an excellent chemical homogeneity at the nanoscale. Magnetic studies show that the frustration (magnetic) parameter (f =âΞCWâ/TM> 27) is significantly enhanced in this new diamond lattice spinel material
Long Range Magnetic Ordering and Magneto-(di) electric Effect in a New Class of High Entropy Spinel Oxide
International audienceHerein, a new class of high entropy spinel material with composition (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)Cr2O4 is introduced. Detailed structural and microstructural characterizations highlight that the sample crystallizes in a cubic spinel structure with an excellent chemical homogeneity at the nanoscale. A peak in the dielectric measurement is observed at the antiferromagnetic ordering temperature (35 K), indicating the possibility of magneto-electric coupling at that temperature. Our study, for the first time, highlights the feasibility to accommodate multiple elements onto a single sublattice in a complex spinel structure and opens new possibilities to design and tailor functional properties in high entropy stabilized correlated electron systems
Long Range Magnetic Ordering and Magneto-(di) electric Effect in a New Class of High Entropy Spinel Oxide
International audienceHerein, a new class of high entropy spinel material with composition (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)Cr2O4 is introduced. Detailed structural and microstructural characterizations highlight that the sample crystallizes in a cubic spinel structure with an excellent chemical homogeneity at the nanoscale. A peak in the dielectric measurement is observed at the antiferromagnetic ordering temperature (35 K), indicating the possibility of magneto-electric coupling at that temperature. Our study, for the first time, highlights the feasibility to accommodate multiple elements onto a single sublattice in a complex spinel structure and opens new possibilities to design and tailor functional properties in high entropy stabilized correlated electron systems
Low Dimensional Magnetic Lattice and Room Temperature Magneto(di)electric Effect in Polyanion RuddlesdenâPopper Iron Oxides
International audienceWe have shown a new design strategy which exploits different oxyanions in a Ruddlesden-Popper (RP)- type phase to modulate the local crystal structure and magnetic lattice. Material (Sr4Fe2(SO4)0.5O6.5) with the larger voluminous oxyanion (SO4, S-O distance = 1.49 Ă
) as separating blocks between magnetic FeO layers shows a twodimensional magnetic lattice. A three-dimensional magnetic lattice and spin reorientation transition is observed for the Sr4Fe2(CO3)O6, having CO3 (C-O distance = 1.25 Ă
), a smaller oxyanion, as a separating layer. Using mixed oxyanions (SO4 and CO3) in the central perovskite block of the RP3 phase, we have demonstrated a facile strategy to modulate the local crystal structure. The modulated displacement of the magnetic cations, which can break the local centrosymmetry, is suggested to originate the magnetodielectric effect near the magnetic ordering temperatures (higher than room temperature). Further, all CO3 containing samples show magnetodielectric coupling below room temperature due to the spin reorientation transition. The room temperature magnetodielectric effect coupled to the targeted local modulation of the crystal structure by oxyanions (in the absence of second-order Jahn-Teller active âdistortion centersâ) opens a new door to the design of new multifunctional materials with the possibility for the room temperature application