Etude d'un nouveau type de fluorure antiferromagnetique a caractere bidimensionnel: NaFeF4

Etude magnetique et par spectroscopie Mössbauer de NH4FeF4

“…3) est caractérisé par un doublet quadrupolaire dont les paramètres sont donnés au tableau II. Le déplacement chimique est très proche de celui ob servé dans de nombreux fluorures de fer trivalent (8,9,12). La valeur de l'éclatement quadrupolaire, quoique très élevée pour un composé du fer trivalent en site octaédrique, est comparable cependant à celles observées pour les phases homologues RbFeF 4 et CsFeF 4 , qui sont de l'ordre de 1,6 mm/s (8, 13, 1 4 ).…”

Topochemical Bottom-Up Synthesis of 2D- and 3D-Sodium Iron Fluoride Frameworks

“…Figure a shows the XRD patterns of products synthesized at different temperatures and time durations. When the mixture was heated to 180 °C for 6 to 24 h, XRD patterns of the corresponding products remained unchanged, and all of them could be indexed with monoclinic layered-NaFeF 4 crystal structure (space group P 2 1 / c ) . Note the reflection at 2θ = 14.7° (denoted by an asterisk) represents a secondary phase, which will be discussed in the following section.…”

“…The as-prepared weberite-Na 2 Fe 2 F 7 cathode has shown the highest insertion voltage with an excellent cycling stability among other iron fluorides that are reported so far. While NaFeF 4 and monoclinic-Na 2 Fe 2 F 7 phases were synthesized previously at high temperatures, , the present approach has not only tailored these materials at relatively low temperatures but also has harvested a new polymorph of Na 2 Fe 2 F 7 in orthorhombic structure, which has been achieved by directing the structural connectivity rooting from the precursor lattice. In the light of topochemical routes utilized to produce battery cathodes, − we expect this bottom-up approach to open new avenues in topochemical synthesis to tailor new higher dimensional alkali ion bearing cathodes based on the low dimensional precursor structures.…”

“…When the mixture was heated to 180 °C for 6 to 24 h, XRD patterns of the corresponding products remained unchanged, and all of them could be indexed with monoclinic layered-NaFeF 4 crystal structure (space group P2 1 /c). 17 Note the reflection at 2θ = 14.7°(denoted by an asterisk) represents a secondary phase, which will be discussed in the following section. Figure 1b depicts the Rietveld refinement of the XRD pattern of 2D-NaFeF 4 obtained from 24 h of dwelling.…”

Etude magnétique et par résonance Mössbauer de l'orthophosphate Na 3Fe2(PO4)3α et d'une phase vitreuse dérivée

“…1 3 ETUDE PAR RÉSONANCE MÔSSBAUER. -LeS spectres Môssbauer ont été obtenus au moyen d'un dispositif classique décrit précédemment [6,7]. (a) : déplacement chimique par rapport au fer a à 293 K. (b) : éclatement quadrupolaire (sa valeur n'a pas été calculée dans l'état antiferromagnétique).…”