R. Olazcuaga

Sur quelques nouvelles phases de formule NaxMnO2 (x ⩽ 1)

Abstract Several new ternary oxides have been isolated in the manganese-oxygen-sodium system for Na Mn ⩽ 1 : Na0.20MnO2, Na0.40MnO2, Na0.44MnO2, Na0.70MnO2+y (0 ⩽ y ⩽ 0.25) and NaMnO2, both with two allotropic varieties. All structures are characterized by edge sharing (MnO6) octahedra, forming double or triple chains for small sodium content and bidimensional layers when the Na Mn ratio becomes close to 1. Electrical and magnetic behaviour of the phases has been determined.

Crystal chemistry of the Na1+xZr2−xLx(PO4)3 (L = Cr, In, Yb) solid solutions☆

Abstract A crystal chemistry study of the three solid solutions Na1+xZr2−xLx(PO4)3 (L = Cr, In, Yb) has been carried out. A Nasicon-type phase is obtained in the range 0 ⩽ x ⩽ xmax.L with xmax.Cr = 2.0, xmax.In = 1.85, xmaxYb = 1.90 at 950°C. All phases have rhombohedral symmetry except Na3Cr2(PO4)3, where a small monoclinic distortion appears at low temperature. Influence of cationic size, electrostatic repulsion and sodium distribution is discussed.

Les phases Na4XO4 (X = Si, Ti, Cr, Mn, Co, Ge, Sn, Pb) et K4XO4 (X = Ti, Cr, Mn, Ge, Zr, Sn, Hf, Pb)

Resume Les phases Na4XO4 (X = Si Ti, Cr, Mn, Co, Ge, Sn, Pb) et K4XO4 (X = Ti, Cr, Mn, Ge, Zr, Sn, Hf, Pb), qui cristallisent dans le systeme triclinique, sont isotypes. Les proprietes optiques et magnetiques ont eteetudiees lorsque X est le chrome, le manganese, ou le cobalt. Elles montrent que lelement de transition occupe un site tetraedrique.

Conductivite ionique dans les systems Na1+xZr2−xLx(PO4)3 (L = Cr, Yb)

Abstract Ionic conductivity measurements in the solid solution Na1+xZr2−xLx(PO4)3 (L = Cr, Yb) have been carried out. The materials have a Nasicon-type structure in a 0 ⩽ x ⩽ xmax.L range (xmax.Cr = 2.0 and xmax.Yb = 1.9). A small monoclinic distortion appears at low temperature for Na3Cr2(PO4)3. As in the Na1+xZr2P3−xSixO12 system a strong increase of the conductivity with rising x has been observed. The results are discussed in connection with temperature and structural parameters.

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.

Etudes electrique et Raman des verres des systemes B2O3M2OM3PO4 (M=Li, Na)

Abstract New glasses with alkali carriers have been prepared in the system B 2 O 3 ue5f8M 2 Oue5f8M 3 PO 4 (M = Li, Na). The variation of the ionic conductivity has been discussed. Raman spectroscopy allows to characterize the behavior of the orthophosphate M 3 PO 4 with respect to the boron-oxygen glass matrix.

Mg0.5Ti2 (PO4)3 : a new member of the NASICON family with low thermal expansion

Abstract Mg 0.5 Ti 2 (PO 4 ) 3 has been prepared by a sol-gel technique and structure determination has been carried out by Rietveld refinement. It belongs to the NASICON-type structure, space group R3c, and is characterized by a low thermal expansion coefficient of 3.7 × 10 −6 K −1 .

Optical properties of Ce1−xPrxO2 powders and their applications to the coloring of ceramics

Abstract The development of red pigments with high temperature stability is of great importance for the ceramic industry. Stabilization of praseodymium (IV) in the refractory oxide CeO 2 leads to cerium-rich solid solutions Ce 1− x Pr x O 2 in the red coloration range. Crystallographic and optical properties have been investigated. The detected color is consistent with Jorgensens model. Thermal stability at high temperature has been studied for various glazes.

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.

The monovalent copper tin phosphate CuISn2(PO4)3

Abstract The monovalent copper tin phosphate Cu I Sn 2 (PO 4 ) 3 was obtained by different chemical ways and its crystallographic data (Nasicon-type R3c) specified. The material was characterized by diffuse reflectance, Mossbauer spectroscopy and 31 P MAS-NMR spectrum. Thermogravimetric measurements are consistent with the existence of the redox Cu 2+ /Cu + system in the network. A structural determination by applying the Rietveld method showed common features with homologous compounds Cu I M 2 (PO 4 ) 3 (M = Ti, Zr) and NaSn 2 (PO 4 ) 3 . This material can play an interesting part from the catalytic point of view in various reactions.