Laureano Moreno-Real

NASICON to scandium wolframate transition in Li1+xMxHf2−x(PO4)3 (M=Cr, Fe): structure and ionic conductivity

a ´´ ´ ´ ´ ´ Abstract The Li M Hf (PO ) (M5 Cr, Fe, Bi) systems have been studied and single phases have been isolated for M 5 Cr 11 xx 22x 43 and Fe. The samples have been characterized by X-ray powder diffraction, diffuse reflectance and impedance spectroscopy. There is a reconstructive transition between rombohedral NASICON and orthorhombic Sc (WO ) -type structures as a 24 3 function of x, at very low values, 0.2 and 0.1 for Cr and Fe, respectively. For the Cr series, a further subtle structural change has been observed for x values higher than 1.7. These phases have the Sc (WO ) -type framework, but the symmetry is 24 3 orthorhombic Pcnb at low values of x and monoclinic P2 / n at high values. The structural changes are discussed on the basis 1 of the sizes of the cavities left by the two frameworks and the lithium order / disorder in these voids. These materials are ionic conductors and their electrical behaviours are also discussed.

Glasses and crystalline A3Al2(PO4)3(A = Na, Li): an impedance and 31P, 27Al, 23Na and 7Li MAS-NMR study

A new vitreous phase with Na3Al2(PO4)3 composition has been prepared. Its crystallisation has been optimised by annealing at low temperature, giving crystalline c-Na3Al2(PO4)3 with Sc2(WO4)3-type structure. The direct synthesis of vitreous Li3Al2(PO4)3 has been attempted but it was unsuccessful. Ion exchange reaction has been carried out in Na3Al2(PO4)3 glass to obtain the lithiated vitreous solid, v-Li3Al2(PO4)3. On heating, v-Li3Al2(PO4)3 decomposes to yield crystalline AlPO4 and Li3PO4 phases. The three solids, with NASICON-like stoichiometries, have been thermal and electrically characterised. DTA and thermodiffractometric studies of the two glass solids have allowed the characterisation of their thermal behaviours including crystallisation. The grain boundary contributions to the total impedance are almost absent in the two vitreous phases. The electrical conductivity values are ∼ 10−6 S cm−1 at 150 °C. The 31P, 23Na, 27Al and 7Li MAS-NMR spectra for these materials provide some insight into the disordered constitution of the vitreous phases and the low mobility of the alkaline cations.

Intercalation of ferrocene and dimethylaminomethylferrocene into α-Sn(HPO4)2•H2O and α-VOPO4•2H2O

The intercalation of ferrocene and dimethylaminomethylferrocene into α-tin(IV) hydrogen phosphate (SnP) and α-vanadyl phosphate has been investigated. Successful intercalation of 0.81 mol of dimethylamino-methylferrocene into α-SnP by an acid-base reaction in aqueous medium to form a bilayer of protonated amines was achieved. However, ferrocene was not intercalated under the same conditions. Intercalation of α-vanadyl phosphate by 0.11 mol of ferrocene in acetonic medium at room temperature was effected by a redox topotactic reaction. The voluminous dimethylaminomethylferrocene was not intercalated into α-vanadyl phosphate.

Intercalation of N-Alkylamines into Mixed Niobyl-Vanadyl Phosphate

Abstract Niobyl-vanadyl phosphate (V0.14Nb0.86)OPO4.2.7 H2O (NbVP) intercalates n-alkylamine molecules to yield stable layered compounds with high basal spacings and compositions close to 1.7 mole of amine and 2 mole of water per mole of phosphate. The X-ray diffraction, differential thermal analysis, thermogravimetry, and IR and diffuse reflectance spectroscopy (UV-vis-nIR) techniques allow us to establish that the amine molecules are protonated in the interlayer space, where the RNH+3 groups interact with the layers via hydrogen bonds. These amines form a molecular bilayer inclined at 58° with respect to the phosphate layers.

Lithium insertion in vanadyl phosphate

Abstract The reaction between LiNO 3 and VOPO 4 ·2H 2 O in acetone medium takes place, besides a redox process, by an acid-basic reaction. The material obtained, Li 1.6 VOPO 4 ·H 2 O, is a non-homogeneous solid, which is converted to a crystalline solid if annealed at 450°C. The existence of lithium ion within the intracrystalline spaces of lithium intercalate as well as the reduction of partial V(v) to V(iv) leads to a mixed ionic-electronic conductor. This fact is confirmed by the impedance spectroscopy study.

Ionic conduction in sepiolite

Abstract The solid state reaction between sepiolite and LiCl at 200°C gives intersalation compounds. The lithium composites obtained, x LiCl-SEP ( x =2, 4, 6 and 8), keep the sepiolite framework but the presence of the halide in its channels causes a gradual breakdown with the increase of temperature. At low temperatures, the polarizing character of Li + induces protonic conductivity in the zeolitic water system. The Cl − and Li + ions move through the channels above 170°C.

Sorption of amides by mixed niobyl-vanadyl phosphate

The layered mixed niobyl-vanadyl phosphate [(V0.l4Nb0.86)OPO4·2.7 H2O] can intercalate different amide molecules. In all cases, the amide I bands [v(CO)] of the original compound shift to lower frequencies, thereby indicating that the amide molecules interact with the layers probablyvia hydrogen bonds linking the coordinated water molecules to the metal atoms. To a lesser extent, primary amides show protonated molecules and tertiary amides show some molecules directly coordinated to the metals, as can be inferred from the bands appearing at 1732 and 1617 cm−1 in the IR spectrum, respectively.

Reaction of niobium phosphate with hydrazine: structural modification

The reaction between hydrazine and NbOPO4·nH2O (n<3) gives an amorphous solid with a high thermal and hydrolitic stability. The presence of hydrazine in the solid has been detected by several bands in the IR spectrum between 1500–1550 cm−1 and 3300–3400 cm−1. The solid maintains its amorphous nature after the elimination of hydrazine at 600°C, and below the crystallization temperature (800°C) we have an amorphous niobium phosphate free of hydrazine possibly with catalytic properties.

Structural and optical properties of hydrated lanthanon uranyl arsenates

Abstract An investigation of the structural and optical properties of the lamellar lanthanon derivatives of hydrogen uranyl arsenate (HUO 2 AsO 4 · 4H 2 O (HUAs)) is reported. The hydrated lanthanon uranyl arsenate compounds have the approximate composition Ln ( UO 2 AsO 4 ) 3 · xH 2 O (LnUAs) ( Ln ≡ La , Ce , Pr , Nd , Sm , Eu , Gd , Tb , Dy , Ho , Er , Tm , Yb and Lu , x ≈ 13–16) and are prepared by intercalation of the lanthanon ions into either HUAs or n -butylammonium uranyl arsenate. Upon intercalation of the tripositive guest ions, the lattice symmetry and crystallinity are reduced, as observed by X-ray powder diffraction. The LnUAs samples exhibit emission characteristic of the UO 2 2+ moiety. Those samples having Ln ≡ Ce , Pr , Nd , Sm , Ho and Er are very weakly emissive, whereas the remaining solids (with Ln ≡ La , Eu , Gd , Tb , Dy , Tm , Yb and Lu ) emit strongly at 298 K when excited with near-UV light. The emissive LnUAs samples have photoluminescence (PL) decay curves that are exponential and yield lifetimes for the strongly emissive samples in the approximate range of 8–100 μs with quantum yields of about 0.02–0.09. From these data, unimolecular radiative and non-radiative rate constants have been calculated for uranyl PL, yielding values of about (5–30) × 10 2 s −1 and about (1–10) × 10 4 s −1 respectively. For EuUAs there is extensive host-to-guest energy transfer, resulting in long-lived emission from the europium guest species. Electronic absorption and PL properties of the LnUAs samples are similar to those of their Ln ( UO 2 PO 4 ) 3 · xH 2 O counterparts

Bilayer formation of 1,4-diazabicyclo[2.2.2]octane (DABCO); intercalation in α-tin hydrogen phosphate

The bisamine 1,4-diazabicyclo[2.2.2]octane (DABCO) has been intercalated into tin(IV) phosphate to give a bilayer and some criteria for bilayer formation with bisamines have been established.