J.M. Dance

EPR of transition metal ions (Mn2+, Cu2+, Cr3+, Fe3+) in fluoroaluminate glasses

Abstract EPR experiments have been performed on glasses related to the CaF2BaF2AlF3 system. Fluctuations of the EPR parameters are observed in the case of divalent ions which occupy distorted sites. The trivalent ions occupy sites of “fully rhombic” symmetry. A comparison with the EPR parameters obtained for crystallized α-CaAlF5 leads to the conclusion that the glass is built up by random type chains containing aluminium separated in various ways by the divalent cations, the coordination numbers of which may differ.

Die Verfeinerung der Weberitstruktur der Verbindung Na2NiFeF7

Eine vollsta¨ndige ro¨ntgenographische Strukturbestimmung an einem Einkristall von Na 2 NiFeF 7 besta¨tigt die orthorhombische Weberitstruktur dieser Verbindung: a = 7.245, b = 10.320, c = 7.458 A, z = 4, Raumgruppe Imm 2, R = 2.9% fuur 527 symmetrieunabha¨ngige Reflexe bei anisotroper Verfeinerung. Entlang der kuurzesten Achse der Elementarzelle sind NiF − 62 -Oktaeder uber Ecken zu Ketten verknuupft, die miteinander in den Richtungen [011] und [01¯1] uuber 4 Ecken von FeF 2 F − 4/ -Oktaedern verbunden sind. Die mittleren Absta¨nde in den verzerrten Oktaedern betragen Ni F = 1.980 bzw. Fe F = 1.933A. Beide Natriuminonen sind 8-fach koordiniert, wobei das eine wie in Pyrochloren eine besonders kurze Achse F Na F (2.16/2.27A) zeigt.

The Nasicon-like copper(II) zirconium phosphate Cu0.5Zr2(PO4)3 and related compounds

Abstract A new family of Nasicon-like zirconium phosphates of formula M 0.5 Zr 2 (PO 4 ) 3 with M = Ca, Cu, Sr, Cd or Pb has been described. The physical properties of the copper compound have been investigated in detail in which Cu 2+ induces a Jahn-Teller distortion below 520°C. Crystal field, electron paramagnetic resonance, and magnetic data are consistent with an elongated octahedral surrounding of the Cu 2+ ions.

The Nasicon-like copper(II) titanium phosphate Cu0.50Ti2(PO4)3

Cu/sub 0.50/Ti/sub 2/(PO/sub 4/)/sub 3/ is a Nasicon-type phase with a cooperative Jahn-Teller distortion below 550/sup 0/C. Crystal field, electron paramagnetic resonance, and magnetic data seem to be consistent with an octahedral surrounding and a d/sub x/sup 2/-y/sup 2///sup 1/ ground state of Cu/sup 2 +/.

Etude par rpe de verres appartenant au systeme CaOB2O3Al2O3 dopes A V4+, Fe3+ et Cu2+

ESR experiments have been performed on glasses belonging to the CaOB2O3Al2O3 system and doped with V4+, Fe3+, Cu2+. In presence of vanadium a VO2+ group is observed with an anisotropic hyperfine structure. The Fe3+ ion is in a distorted “network forming” position yielding the g ≅ 4.28 value. Cu2+ is located in a tetragonally elongated octahedron in a “network modifying” site. Its Jahn-Teller character gives rise also to an anisotropic hyperfine structure.

Na4Nb(PO4)3, a material with a reversible crystal-glass transformation: Structural and optical comparison

Abstract The phosphate Na 4 Nb(PO 4 ) 3 exhibits a reversible crystal-glass phase change. Raman and optical investigations give evidence of the similarity between the covalent skeleton of the Nasicon-like crystalline phosphate and the network of the glass. Both types of materials contain octahedral NbO 6 groups with various Nb O lengths. It is shown for the neodymium-doped glasses that these structural features induce a strong self concentration quenching of the Nd 3+ emission.

On a new hydrogenated Cu (I) nasicon-type phosphate H0.5CuI0.5Zr2(PO4)3

Absorption of hydrogen in CuII0.5Zr2(PO4)3 gives rise to a new Cu (I) Nasicon-type derived phosphate H0.5CuI0.5Zr2(PO4)3 as the result of an intercalation process. Various physical properties have been investigated. The copper (I) luminescence has been explained on hand of the position of the lowest levels of the Cu (I) 3d94s1 electronic configuration within the forbidden gap.

Etude cristallographique et par effet Mössbauer du fluorure ferrimagnétique Na5Fe3F14γ

The structure of ferrimagnetic γ-Na5Fe3F14 has been determined by single-crystal X-ray diffraction. The cell is tetragonal with space group P42212 and parameters a = 7.345 ± 0.007 A and c = 10.400 ± 0.007 A. The iron atoms occupy a twofold and a fourfold position in the lattice and are octahedrally surrounded by fluorines. These octahedra share corners and form two-dimensional layers of formula (Fe3F14)5n−n. The Mossbauer spectra were measured from 4.2 to 293°K and the results are discussed in terms of the position and environment of iron atoms in the lattice.

Interactions magnetiques dans les fluorures de type weberite

Abstract In the fluorides of weberite type the various magnetic behaviours have been correlated with structure and nature of the cations.

Etude magnetique des composes Na5M3F14 (M = V, Fe, Co) de type chiolithe

Abstract The magnetic properties of the ferrimagnetic chiolithe-type phases Na 5 V 3 F 14 , Na 5 Fe 3 F 14 , Na 5 Fe 2 CoF 14 , Na 5 Co 3 F 14 have been investigated. Explaination of the obtained results have been proposed.