G. Le Flem

Ionic conductivity of oxides with general formula LixLn1/3Nb1−xTixO3 (Ln = La, Nd)

Abstract Ionic conductivity of phases with general formulaLi x Ln 1/3 Nb 1− x Ti x O 3 ( Ln =La, Nd)has been determined for materials with a small value of x , i.e., in composition range with a Ln 1/3 NbO 3 perovskite related structure. The possible influence on the transport properties of the 2D character of the vacancy sublattice has been investigated by a NMR study on Li 0.05 Nb 0.95 Ti 0.05 O 3 .

Optical non-linearity in oxide glasses

The origin of the optical non-linear response has been investigated in two different types of oxide glasses. Linear and non-linear refractive indices have been obtained by interferometric measurements. Correlations between the local structure of polarizable entities within glasses and their optical activities have been tentatively established through ab initio calculations.

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.

Nonlinear optical properties of some tellurium (IV) oxide glasses

Abstract Thermal and optical properties of glasses of the TeO 2 | ZnO, TeO 2 | Nb 2 O 5 and TeO 2 | M 2 O | Nb 2 O 5 (M = Li, K) systems have been investigated. Linear and nonlinear indices of the materials increase with the TeO 2 rate. The highest values are obtained for the niobium tellurite glasses emphasizing the particularly significant role of NbO 6 octahedra in the optical response.

Structure and thermal expansion of LiGe2(PO4)3

Abstract LiGe2(PO4)3 belongs to the Nasicon-type family. Room-temperature structure has been determined on a single crystal from 3D X-ray data. Thermal evolution of this structure has been established from neutron powder diffraction data between 300 and 1000 K using the Rietveld method. The thermal expansion is positive along the c-axis, whereas shrinking is observed along the a-axis below 900 K, followed by dilatation. The atomic displacements noted with increasing temperature are consistent with a model proposed for NaZr2(PO4)3.

Magnetic interactions in the layer compounds MPX3 (M = Mn, Fe, Ni; X = S, Se)

Abstract The mpx3 phases (M = Mn, Fe, Ni; X = S, Se) with sheet structures are insulators with localized moments. They show antiferromagnetic ordering at low temperatures. From the magnetic structures determined by neutron diffraction the magnetic interactions are considered and shown to be characteristic of 2D behavior.

Correlations between structural properties of Nb2O5NaPO3Na2B4O7 glasses and non-linear optical activities

Abstract Information about the origin of the optical non-linear response in transparent glasses can be gained from a detailed structure investigation using Raman and X-ray absorption spectroscopies. The effects resulting from the introduction of niobium oxide in the sodium borophosphate matrix of composition 0.95NaPO 3 0.05Na 2 B 4 O 7 are described. For small niobium concentrations, the formation of distorted NbO 6 octahedra is observed. The increase of niobium concentration allows the progressive linking of corner-shared and less distorted octahedra. The correlative evolution of the measured third order susceptibilities χ (3) is analyzed on the basis of the bond orbital theory. A good agreement between experimental and calculated χ (3) is obtained as long as the NbO 6 entities are isolated from each other, but the clustering of these entities increases the non-linear response, χ (3) .

White light emitting glasses

Abstract For the first time vitreous materials capable of generating “white light” by simultaneous emission of blue, green, and red emitting fluorescent centers have been produced. These glasses are B 2 O 3 -based and contain Ce 3+ , Tb 3+ , and Mn 2+ as activators. Both chromaticity coordinates and luminescence intensity vary vs glass composition and activator concentration. The spectroscopic properties of singly, doubly, and triply doped glasses are reported. Ce 3+ shows a broad-band emission centered at the border between UV and visible light domains. Moreover, this ion acts as a donor in codoped glasses, transferring part of its energy to Tb 3+ and Mn 2+ , whose luminescence occurs respectively in the green and red parts of the visible. The mechanisms of the various energy transfers observed have been investigated by a detailed kinetic investigation.

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.

Luminescent properties of delafossite-type oxides LaCuO2 and YCuO2

Abstract Investigation of luminescent properties of delafossite-type CuLaO 2 and CuYO 2 oxides shows two emission bands resulting from two separated excitation bands: the emission band of lower energy results from the excitation to highest energy, exhibiting thus a larger Stokes shift. The existence of a single site for Cu + ions suggests a simple model involving two emitting levels: one corresponding to a 3 d 9 4 s 1 configuration and the other to a 3 d 9 4 p x , y 1 configuration.