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Title: Structural and thermal studies of H{sub 2}La{sub 2/3}Ta{sub 2}O{sub 7}, a protonated layered perovskite

Abstract

We have synthesised the new protonated layered perovskite H{sub 2}La{sub 2/3}Ta{sub 2}O{sub 7} which is related to the Ruddlesden-Popper family. This compound is obtained by ionic exchange starting from Li{sub 2}La{sub 2/3}Ta{sub 2}O{sub 7} maintained in dilute HNO{sub 3} at 60 deg. C. Thermal X-ray diffraction and DTA/TGA revealed interesting dehydration properties with formation of a layered anhydrous phase leading at higher temperature (1550 deg. C) to La{sub 1/3}TaO{sub 3}. This latter compound exhibits the original lanthanum ordering expected similarly to that of the Li form, while at 900 deg. C a metastable form, presenting a disordered La distribution, is observed.

Authors:
 [1];  [1];  [1]
  1. Laboratoire des Oxydes et Fluorures (UMR 6010 CNRS), Institut de Recherche en Ingenierie Moleculaire et Materiaux Fonctionnels (FR 2575 CNRS), Universite du Maine, Avenue O. Messiaen, 72085 Le Mans Cedex 9 (France)
Publication Date:
OSTI Identifier:
20891666
Resource Type:
Journal Article
Resource Relation:
Journal Name: Materials Research Bulletin; Journal Volume: 41; Journal Issue: 4; Other Information: DOI: 10.1016/j.materresbull.2005.10.003; PII: S0025-5408(05)00378-8; Copyright (c) 2005 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; DEFECTS; DEHYDRATION; DIFFERENTIAL THERMAL ANALYSIS; ION EXCHANGE; LANTHANUM; LANTHANUM OXIDES; MICROSTRUCTURE; NITRIC ACID; PEROVSKITE; PHASE TRANSFORMATIONS; TANTALUM OXIDES; THERMAL GRAVIMETRIC ANALYSIS; TRANSMISSION ELECTRON MICROSCOPY; X-RAY DIFFRACTION

Citation Formats

Le Berre, F., Crosnier-Lopez, M.P., and Fourquet, J.L. Structural and thermal studies of H{sub 2}La{sub 2/3}Ta{sub 2}O{sub 7}, a protonated layered perovskite. United States: N. p., 2006. Web. doi:10.1016/j.materresbull.2005.10.003.
Le Berre, F., Crosnier-Lopez, M.P., & Fourquet, J.L. Structural and thermal studies of H{sub 2}La{sub 2/3}Ta{sub 2}O{sub 7}, a protonated layered perovskite. United States. doi:10.1016/j.materresbull.2005.10.003.
Le Berre, F., Crosnier-Lopez, M.P., and Fourquet, J.L. Thu . "Structural and thermal studies of H{sub 2}La{sub 2/3}Ta{sub 2}O{sub 7}, a protonated layered perovskite". United States. doi:10.1016/j.materresbull.2005.10.003.
@article{osti_20891666,
title = {Structural and thermal studies of H{sub 2}La{sub 2/3}Ta{sub 2}O{sub 7}, a protonated layered perovskite},
author = {Le Berre, F. and Crosnier-Lopez, M.P. and Fourquet, J.L.},
abstractNote = {We have synthesised the new protonated layered perovskite H{sub 2}La{sub 2/3}Ta{sub 2}O{sub 7} which is related to the Ruddlesden-Popper family. This compound is obtained by ionic exchange starting from Li{sub 2}La{sub 2/3}Ta{sub 2}O{sub 7} maintained in dilute HNO{sub 3} at 60 deg. C. Thermal X-ray diffraction and DTA/TGA revealed interesting dehydration properties with formation of a layered anhydrous phase leading at higher temperature (1550 deg. C) to La{sub 1/3}TaO{sub 3}. This latter compound exhibits the original lanthanum ordering expected similarly to that of the Li form, while at 900 deg. C a metastable form, presenting a disordered La distribution, is observed.},
doi = {10.1016/j.materresbull.2005.10.003},
journal = {Materials Research Bulletin},
number = 4,
volume = 41,
place = {United States},
year = {Thu Apr 13 00:00:00 EDT 2006},
month = {Thu Apr 13 00:00:00 EDT 2006}
}
  • The layered-structural ceramics, such as lanthanum titanate (La{sub 2}Ti{sub 2}O{sub 7}), have been known for their good temperature and low dielectric loss at microwave frequencies that make them good candidate materials for high frequency applications. However, few studies have been conducted on the synthesis optimization by sol gel reaction, in particular by acrylamide polymerization route. The interest in La{sub 2}Ti{sub 2}O{sub 7} ceramic has been greatly increased recently due to the effect of oriented grains. This anisotropy of the microstructure leads to anisotropy in dielectric, electrical and mechanical properties. In this study, grain oriented lanthanum titanate was produced by themore » sol–gel acrylamide polymerization route. The characterizations of the samples were achieved by thermal analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). X-ray diffraction indicates that the formation of monoclinic perovskite La{sub 2}Ti{sub 2}O{sub 7} nanocrystals is a necessary first step to obtain orthorhombic LaTiO{sub 3} nanocomposites (with space group Pbnm). In this work we identified that the monoclinic perovskite La{sub 2}Ti{sub 2}O{sub 7} with space group P2{sub 1} transforms its structure into one with the orthorhombic space group Cmc2{sub 1} at approximately 1073 K. The microstructure associated consisted of flaky monoclinic La{sub 2}Ti{sub 2}O{sub 7} nanocomposites in comparison with round-shaped LaTiO{sub 3} nanocomposites. - Highlights: • The flaky-like La{sub 2}Ti{sub 2}O{sub 7} compound was synthesized by sol–gel acrylamide route. • Simultaneous monitoring of the DTA and XRD with temperature was performed. • Phase transformation characterization of La{sub 2}Ti{sub 2}O{sub 7} has been carried out. • The variation of the La{sub 2}Ti{sub 2}O{sub 7} and LaTiO{sub 3} grain morphology has been compared.« less
  • Hydrothermal reactions of molybdenum-oxide precursors with polyalcohols in the presence of base yielded two series of mixed-valence oxomolybdenum clusters, the hexadecanuclear species [XH{sub 12}(Mo{sup VI}O{sub 3}){sub 4}Mo{sup V}{sub 12}O{sub 40}]{sup m{minus}}(X=Na{sup +}, m=7; X=2H{sup +}, m=6) and the superclusters [XH{sub n}Mo{sup VI}{sub 6}Mo{sup V}{sub 36}O{sub 109}(OCH{sub 2}){sub 3}CR{sub 7}]{sup m{minus}} (X=Na-(H{sub 2}O){sub 3}{sup +}, m=9, n=13; X=Na(H{sub 2}O){sub 3}{sup +}, m=7, n=15; X=MoO{sub 3}, m=9, n=14; X=MoO{sub 3}, m=10, n=13). In a representative synthesis for the hexadencanuclear class of materials, the hydrothermal reaction of a mixture of Na{sub 2}MoO{sub 4}{center_dot}2H{sub 2}O, MoO{sub 3}, Mo metal, and NH{sub 4}Cl produced (NH{submore » 4}){sub 7}[NaMo{sub 16}(OH){sub 12}O{sub 40}]{center_dot}4h{sub 2}O (1{center_dot}4H{sub 2}O) as red-orange crystals. The compound (Me{sub 3}NH){sub 4}K{sub 2}[H{sub 2}Mo{sub 16}(OH){sub 40}]{center_dot}8H{sub 2}O(2{center_dot}8H{sub 2}O(2{center_dot}8H{sub 2}O) was prepared in a similar fashion. The structure of the anion of 1 consists of an {epsilon}-Keggin core H{sub 12}Mo{sub 12}O{sub 40}, capped on four hexagonal faces by MoO{sub 3} units and encapsulating a Na{sup +} cation. The structure of the oxomolybdenum framework of 2 is essentially identical to that of 1; however, the central cavity is now occupied by 2H{sup +}.« less
  • Two compounds of formula La{sub 7}A{sub 3}W{sub 4}O{sub 30} (with A=Nb and Ta) were prepared by solid-state reaction at 1450 and 1490{sup o}C. They crystallize in the rhombohedric space group R-3 (No. 148), with the hexagonal parameters: a=17.0640(2)A, c=6.8859(1)A and a=17.0701(2)A, c=6.8851(1)A. The structure of the materials was analyzed from X-ray, neutron and electronic diffraction. These oxides are isostructural of the reduced molybdenum compound La{sub 7}Mo{sub 7}O{sub 30}, which are formed of perovskite rod along [111]. An order between (Nb, Ta) and W is observed.
  • The microstructural and luminescent properties of H{sub 1.77}[Sr{sub 0.8}Bi{sub 0.21}Ta{sub 2}O{sub 7}] powders under different dehydrating conditions were investigated. The powders were obtained by protonating Bi{sub 2}SrTa{sub 2}O{sub 9} powders in 3 M aqueous HCl solution, and were dehydrated by a post-annealing in air from 250 to 700 {sup o}C. The photoluminescence was enhanced for all dehydrated powders, especially for the sample annealed at 400 {sup o}C. The thermogravimetric analysis showed that there is an obvious dehydration temperature range from 200 to 400 {sup o}C, which was corresponding to the changing of the microstructure and photoluminescence in the same temperaturemore » range. The mechanism behind the experimental results was discussed.« less
  • The perovskite-related layered structure of La{sub 2}Ti{sub 2}O{sub 7} has been studied at pressures up to 30 GPa using synchrotron radiation powder X-ray diffraction (XRD) and Raman scattering. The XRD results indicate a pronounced anisotropy for the compressibility of the monoclinic unit cell. The ratio of the relative compressibilities along the [100], [010] and [001] directions is {approx}1:3:5. The greatest compressibility is along the [001] direction, perpendicular to the interlayer. A pressure-induced phase transition occurs at 16.7 GPa. Both Raman and XRD measurements reveal that the pressure-induced phase transition is reversible. The high-pressure phase has a close structural relation tomore » the low-pressure monoclinic phase and the phase transition may be due to the tilting of TiO{sub 6} octahedra at high pressures. - Graphical abstract: La{sub 2}Ti{sub 2}O{sub 7} is a layered perovskite and it shows anisotropic compressibility at high pressures. The in situ XRD and Raman measurements indicate a structural transformation takes place at 16.7 GPa.« less