Gilles Le Flem

The crystal structure of a new high -Nd- concentration laser material: Na3Nd(PO4)2

The crystal structure of Na3Nd(PO4)2 has been determined from three-dimensional Mo-Kα diffractometer data. The space group is Pbc21, the lattice constants are: a = 15.874(8) Ab = 13.952(8) Ac = 18.470(9) A and there are 24 formula units per unit cell, giving a Nd concentration of 5.8 1021cm−3. The final R-factor with 2329 independent reflections is 0.060. The structure of Na3Nd(PO4)2, very closely related to that of Na3La(VO4)2, is made up of isolated PO4 tetrahedra and of sodium and neodymium atoms arranged in an ordered way. The tripling of the a parameter results only from the distortion of the PO4 tetrahedra. The NdOy polyhedra are isolated from one another and the shortest Nd-Nd distance is 4.65 A.

Relations between structure and physical properties in K2NiF4-type oxides

Abstract It is possible to predict the electronic configuration of cations such as Fe(IV), Co(III), and Ni(III) in K2NiF4-type oxides on the base of elementary structural and bonding considerations and to describe the more or less two-dimensional character of the magnetic interactions within the layers containing the 3d ions.

Ioni conductivity in Nasicon-type phases Na1+xZr2−xLx(PO4)3 (L = Cr, In, Yb)

Abstract The crystal chemistry of solid solutions of formula Na1+xZr2−xLx(PO4)4 (L = Cr, In, Yb) (0⩽x⩽xLmax) has been investigated. In each system a Nasicon-type phase is obtained, with xCrmax = 2.0, xInmax = 1.85 and xYbmax = 1.90. All phases have rhombohedral symmetry (space group: R 3 c) except for the composition Na3Cr2(PO4)3 where a small monoclinic distortion is detected at room temperature (space group: C2/c or Cc). The variation with x of the cell parameter is discussed. The ionic conductivity of all these materials increases strongly with sodium content up to a value of x(xLσ max) for which a maximum is observed. The conductivity versus reciprocal temperatures curves of Na3Cr2(PO4)3 show two slopes (ΔE = -0.42 and 1.1 eV) corresponding respectively to the rhombohedral and monoclinic forms. The behavior of the materials is discussed as a function of sodium content, sodium distribution in available sites, cation sizesand lattice covalency.

Etude comparative des proprietes magnetiques des oxydes lamellaires ACrO2 (A = Li, Na, K)—II: Calcul des integrales d'echange

Abstract The magnetic properties of 2-D antiferromagnetic A CrO 2 ( A = Li, Na, K) phases have been investigated by susceptibility measurements. They have been interpreted on the basis of a Heisenberg Rushbrooke and Woods model. The exchange integral decreases from lithium to potassium.

The sodium ytterbium orthophosphate Na3(1+x)Yb(2-x)(PO4)3

A new sodium ytterbium orthophosphate with general formula Na3(1+x)Yb(2-x)(PO4)3 (0.07 ⩽ x ⩽ 0.50) has been prepared and characterized. Its crystal structure has been determined from a single crystal for x = 0.50. The space group is R3c, the lattice constants are : a = 9.12(1) A, c = 21.81(6) A. The structure of Na4.50Yb1.50(PO4)3 is related to that of NaZr2(PO4)3. The PO4 tetrahedra and the (Yb,Na)O6 octahedra form a three-dimensional skeleton in which the remaining sodium atoms are inserted. This structural type is also found for the phases Na4.50Ln1.50(PO4)3 (Ln = Tm, Lu) and Na4.50Ln1.50(AsO4)3 (Ln = Er, Tm, Yb, Lu).

Proprietes magnetiques de la phase Sr1,50La0,50MnO4

Abstract The crystallographic, electrical and magnetic properties of Sr 1,50 La 0.50 MnO 4 which has a K 2 NiF 4 -type structure show the existence of ferromagnetic clusters due to Mn 3+ Mn 4+ short range ordering antiferromagnetically coupled.

Optical spectroscopy of monovalent copper-doped borate glasses

Abstract The introduction of copper ions into borate glasses induces in the visible optical region a strong broad fluorescence which is shown to be characteristic of Cu+ ions occupying a large variety of sites.

Etudes cristallographique magnétique et par résonance Mössbauer de la variété de haute température du pyrophosphate NaFeP2O7

Abstract Single crystals of the high-temperature form of NaFeP 2 O 7 have been grown by a flux technique. II-NaFeP 2 O 7 crystallizes in the monoclinic P2 1 c space group with lattice parameters: a = 7.298(2) A, b = 7.874(2) A, c = 9.536(3) A, β = 111.85(2)°. The structure refined from 1481 independent reflections leads to R = 0.044 and confirms the work previously published by M. Gabelica-Robert, M. Goreaud, P. Labbe, and B. Raveau ( J. Solid State Chem. 45, 389, 1982). Magnetic Mossbauer resonance studies have shown the existence of antiferromagnetic ordering with a weak ferromagnetic component below 30 K. The FeO bond is markedly ionic in character due to the highly polarizing power of phosphorus in tetrahedral site.

Les phases SrLa2Al2O7 et SrGd2Al2O7

Abstract SrLa2Al2O7 and SrGd2Al2O7 belong to the structural type Sr3Ti2O7. In SrGd2Al2O7 strontium and gadolinium occupy respectively the 12 and 9 coordinated sites, whereas in SrLa2Al2O7 the homologous cations are statistically distributed. The fluorescence spectra of both phases activated by Eu3+ ions show that the only possible position of Eu3+ is the 9 coordinated site.

Etude comparative des proprietes magnetiques des oxydes lamellaires ACrO2 (A = Li, Na, K)—I: Etude par effet Mössbauer de LiCrO2 dope par le fer

Abstract A Mossbauer study of the dimensionality of magnetic interactions in the layer oxide LiCr 0.99 Fe 0.01 O 2 shows a 2-D behaviour.