R. Salmon

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.

The structures of the Na3Ln(XO4)2 phases (Ln = rare earth, X = P, V, As)

A complete and detailed structural description of sodium rare-earth orthophosphates, orthovanadates and orthoarsenates, with general formula Na3Ln(XO4)2 (Ln = rare-earth, X = P, V, As), is presented. Their structural evolution has been studied not only as a function of the Ln3+ ion size and the (XO4)3− group, but also as a function of temperature.

Les phases SrLnMnO4 (Ln = La, Nd, Sm, Gd), BaLnMnO4 (Ln = La, Nd) et M1+xLa1−xMnO4 (M = Sr, Ba)

Abstract The phases SrLnMnO4 (Ln = La, Nd, Sm, Gd), BaLnMnO4 (Ln = La, Nd) and the solid solutions M1+xLa1−xMnO4 (M = Sr: 0 ⩽ x ⩽ 1; M = Ba: 0 ⩽ x ⩽ 0.50) have a K2NiF4-type structure. The c a ratio of the unit cell is related to the electronic configuration of the Mn3+ ions.

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).

Blood haemolysis by ceramics

Ceramics are more and more frequently under consideration for construction of blood-contacting devices, i.e. cardiac valves or cardiac assist devices. This study evaluated the haemolysis eventually initiated in vitro by ceramic powders (Al2O3, ZrO2/Y2O3, AlN, B4C, BN, SiC, Si3 N4, TiB2, TiN, TiC), graphite and diamond. The chemical composition of the powders was studied by X-ray microprobe and various other methods, and BET specific areas were determined. The haemolysis was almost zero for all powders, except AlN which showed slight haemolysis and TiB2 which had high haemolytic power.

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.

On some new efficient luminophors with low-concentration quenching effects

Abstract New phosphors very efficient under uv excitation Na 3 Ce 1− x Tb x (PO 4 ) 2 and Na 3 La 1− x Gd x (PO 4 ) 2 , have been proposed. The high resolution emission of Gd 3+ in Na 3 Gd(PO 4 ) 2 and the non-radiative energy transfer from Gd 3+ to Tb 3+ in Na 3 Gd 1− x Tb x (PO 4 ) 2 have been studied.

Preparation of spherical and controlled size particles of silica or tantalum oxide by chemical reaction in aerosols

Abstract Spherical particles of silica or tantalum oxide were prepared by the hydrolysis of aerosols consisting of silicon tetrachloride or tantalum pentaethoxide, respectively, diluted in propanol-2. Silica particles so-obtained were spherical but agglomerated, and of a rather broad size distribution. However, the particles of tantalum oxide prepared were spherical, non-agglomerated and of narrow size distribution; the mean diameter ranged between 0.84 and 1.72 μm, depending on temperature and the gas flow rate. In both cases the particles were amorphous and crystallized after calcination at high temperature.

The influence of sintering on the electrical conductivity of the Zn0.99Co0.01O solid solution

Abstract The electrical properties of a phase of composition close to Zn 0.99 Co 0.01 O have been studied on pellets sintered at 1300°C under a pure oxygen stream for various periods of time. Plotting of electrical conductivity vs. temperature shows two domains characterized by two different activation energies. The high temperature activation energy depends on sintering time. The authors suggest that this property could be due to non-statistical distribution of cobalt and evaporation of zinc oxide.

Influence des variétés allotropiques de Bi2O3 sur les caractéristiques électriques des varistances à base d'oxyde de zinc

Abstract The I–V characteristics of zinc oxide-based varistors have been studied as a function of the variety of bismuth oxide stabilized during the cooling process. An improvement of the nonlinear exponent at low current densities and a minor change in the characteristics after a pulse of current are observed for slowly cooled samples.