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Title: Structure and dielectric characterization of a new A-site deficient La{sub 5/3}MgTaO{sub 6} perovskite

Abstract

The crystal structure of new A-site deficient La{sub 5/3}MgTaO{sub 6} perovskite was investigated by neutron, X-ray and electron diffraction. Neutron and X-ray powder diffraction spectra were refined in the monoclinic I2/m space group, with the parameters of the unit cell a=5.6304(2)A, b=5.6226(2)A, c=7.9434(2)A and {beta}=90.04(1){sup o}. This structural model presumes a random distribution of the vacancies and takes into account both a rock salt-type Mg{sup 2+}/Ta{sup 5+} cation ordering and a{sup -}a{sup -}c{sup 0} configuration of the octahedral tilting. Electron diffraction showed that the crystal structure is more complex at the local level due to a short-range vacancy ordering. This observation in combination with the symmetry analysis leads to the conclusion that the C2/m symmetry with 2{radical}2a{sub p}x2{radical}2a{sub p}x2a{sub p} supercell is more adequate for the description of the crystal structure in the local level. Dielectric measurements performed in a wide frequency range were correlated with the crystal structure and compared with other ordered double perovskites. Far-infrared spectroscopy was used to characterize the lattice contribution to the dielectric response at the microwave frequencies. The complex dielectric function was evaluated and extrapolated down to the gigahertz range. The effect of the vacancies on the intrinsic dielectric losses is discussed based onmore » the spatial phonon correlation model.« less

Authors:
 [1];  [2];  [2];  [3];  [4];  [4];  [4]
  1. Department of Ceramics and Glass Engineering, CICECO, University of Aveiro, Aveiro 3810-193 (Portugal), E-mail: dkhalyavin@cv.ua.pt
  2. Department of Ceramics and Glass Engineering, CICECO, University of Aveiro, Aveiro 3810-193 (Portugal)
  3. Hahn-Meitner-Institut, Glienicker Strasse 100, Berlin D-14109 (Germany)
  4. Department of Physics, University of Minho, Braga 4710-057 (Portugal)
Publication Date:
OSTI Identifier:
21015616
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 180; Journal Issue: 1; Other Information: DOI: 10.1016/j.jssc.2006.09.016; PII: S0022-4596(06)00526-3; Copyright (c) 2006 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:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ABSORPTION SPECTROSCOPY; DIELECTRIC MATERIALS; DIELECTRIC PROPERTIES; ELECTRON DIFFRACTION; FREQUENCY RANGE; INFRARED SPECTRA; LANTHANUM COMPOUNDS; MAGNESIUM COMPOUNDS; MAGNESIUM IONS; MICROWAVE RADIATION; MONOCLINIC LATTICES; NEUTRON DIFFRACTION; OXIDES; PEROVSKITE; SPACE GROUPS; STRUCTURAL MODELS; SYMMETRY; TANTALUM COMPOUNDS; TANTALUM IONS; VACANCIES; X-RAY DIFFRACTION

Citation Formats

Khalyavin, D.D., Senos, A.M.R., Mantas, P.Q., Argyriou, D.N., Tarroso Gomes, I., Vieira, L.G., and Ribeiro, J.L. Structure and dielectric characterization of a new A-site deficient La{sub 5/3}MgTaO{sub 6} perovskite. United States: N. p., 2007. Web. doi:10.1016/j.jssc.2006.09.016.
Khalyavin, D.D., Senos, A.M.R., Mantas, P.Q., Argyriou, D.N., Tarroso Gomes, I., Vieira, L.G., & Ribeiro, J.L. Structure and dielectric characterization of a new A-site deficient La{sub 5/3}MgTaO{sub 6} perovskite. United States. doi:10.1016/j.jssc.2006.09.016.
Khalyavin, D.D., Senos, A.M.R., Mantas, P.Q., Argyriou, D.N., Tarroso Gomes, I., Vieira, L.G., and Ribeiro, J.L. Mon . "Structure and dielectric characterization of a new A-site deficient La{sub 5/3}MgTaO{sub 6} perovskite". United States. doi:10.1016/j.jssc.2006.09.016.
@article{osti_21015616,
title = {Structure and dielectric characterization of a new A-site deficient La{sub 5/3}MgTaO{sub 6} perovskite},
author = {Khalyavin, D.D. and Senos, A.M.R. and Mantas, P.Q. and Argyriou, D.N. and Tarroso Gomes, I. and Vieira, L.G. and Ribeiro, J.L.},
abstractNote = {The crystal structure of new A-site deficient La{sub 5/3}MgTaO{sub 6} perovskite was investigated by neutron, X-ray and electron diffraction. Neutron and X-ray powder diffraction spectra were refined in the monoclinic I2/m space group, with the parameters of the unit cell a=5.6304(2)A, b=5.6226(2)A, c=7.9434(2)A and {beta}=90.04(1){sup o}. This structural model presumes a random distribution of the vacancies and takes into account both a rock salt-type Mg{sup 2+}/Ta{sup 5+} cation ordering and a{sup -}a{sup -}c{sup 0} configuration of the octahedral tilting. Electron diffraction showed that the crystal structure is more complex at the local level due to a short-range vacancy ordering. This observation in combination with the symmetry analysis leads to the conclusion that the C2/m symmetry with 2{radical}2a{sub p}x2{radical}2a{sub p}x2a{sub p} supercell is more adequate for the description of the crystal structure in the local level. Dielectric measurements performed in a wide frequency range were correlated with the crystal structure and compared with other ordered double perovskites. Far-infrared spectroscopy was used to characterize the lattice contribution to the dielectric response at the microwave frequencies. The complex dielectric function was evaluated and extrapolated down to the gigahertz range. The effect of the vacancies on the intrinsic dielectric losses is discussed based on the spatial phonon correlation model.},
doi = {10.1016/j.jssc.2006.09.016},
journal = {Journal of Solid State Chemistry},
number = 1,
volume = 180,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • A solid solution system of the double perovskite La{sub 2/3}TiO{sub 3} and the GdFeO{sub 3}-type perovskite CaTiO{sub 3}, (1{minus})xCaTiO{sub 3}-xLa{sub 2/3}TiO{sub 3} has been prepared to investigate the crystal structure and the dielectric properties. In this system, the structure changed from pseudo-cubic perovskite to tetragonal double perovskite at x{approx}0.7, and to orthorhombic double perovskite at x{approx}0.9. Microwave dielectric measurement showed a decrease in dielectric constant and temperature coefficient of the resonant frequency and an increase in Q value with increasing x. The sample with x{approx}0.96 showed excellent microwave characteristics, especially high Q(2700) along with high {var_epsilon}{sub r} at 10 GHz.more » In the low frequency dielectric measurement, dielectric relaxation could be observed in the composition range x{le}0.3. The dielectric relaxation showed strikingly different behaviors depending on the annealing process in oxygen after sintering.« less
  • The vacancy ordering behavior of an A-site deficient perovskite system, Ca 1–xLa 2x/3TiO 3, was studied using atomic resolution scanning transmission electron microscopy (STEM) in conjunction with electron energy-loss spectroscopy (EELS), with the aim of determining the role of A-site composition changes. At low La content (x = 0.2), adopting Pbnm symmetry, there was no indication of long-range ordering. Domains, with clear boundaries, were observed in bright-field (BF) imaging, but were not immediately visible in the corresponding high-angle annular dark-field (HAADF) image. These boundaries, with the aid of displacement maps from A-site cations in the HAADF signal, are shown tomore » be tilt boundaries. At the La-rich end of the composition (x = 0.9), adopting Cmmm symmetry, long-range ordering of vacancies and La 3+ ions was observed, with alternating La-rich and La-poor layers on (001)p planes, creating a double perovskite lattice along the c axis. These highly ordered domains can be found isolated within a random distribution of vacancies/La 3+, or within a large population, encompassing a large volume. In regions with a high number density of double perovskite domains, these highly ordered domains were separated by twin boundaries, with 90° or 180° lattice rotations across boundaries. In conclusion, the occurrence and characteristics of these ordered structures are discussed and compared with similar perovskite systems.« less
  • The vacancy ordering behavior of an A-site deficient perovskite system, Ca 1–xLa 2x/3TiO 3, was studied using atomic resolution scanning transmission electron microscopy (STEM) in conjunction with electron energy-loss spectroscopy (EELS), with the aim of determining the role of A-site composition changes. At low La content (x = 0.2), adopting Pbnm symmetry, there was no indication of long-range ordering. Domains, with clear boundaries, were observed in bright-field (BF) imaging, but were not immediately visible in the corresponding high-angle annular dark-field (HAADF) image. These boundaries, with the aid of displacement maps from A-site cations in the HAADF signal, are shown tomore » be tilt boundaries. At the La-rich end of the composition (x = 0.9), adopting Cmmm symmetry, long-range ordering of vacancies and La 3+ ions was observed, with alternating La-rich and La-poor layers on (001)p planes, creating a double perovskite lattice along the c axis. These highly ordered domains can be found isolated within a random distribution of vacancies/La 3+, or within a large population, encompassing a large volume. In regions with a high number density of double perovskite domains, these highly ordered domains were separated by twin boundaries, with 90° or 180° lattice rotations across boundaries. In conclusion, the occurrence and characteristics of these ordered structures are discussed and compared with similar perovskite systems.« less
  • A new oxygen-deficient perovskite corresponding to the formulation La/sub 8-x/Sr/sub x/Cu/sub 8/O/sub 20-epsilon/ (1.28 less than or equal to x less than or equal to 1.92) has been isolated. The results of chemical analysis show that copper exhibits a mixed valence in this oxide. This perovskite crystallizes in a tetragonal cell with parameters related to the a/sub p/ parameter of the cubic perovskite by: a approx. = a/sub p/ 2 ..sqrt.. 2, c approx. = a/sub p/. The structure has been determined by neutron powder diffraction in the space group p4mbm. This study shows that the oxygen vacancies are ordered,more » forming rows parallel to (001). The (Cu/sub 8/O/sub 20/) framework is built of corner-sharing CuO/sub 6/ octahedra. CuO/sub 5/ pyramids, and CuO/sub 4/ square planar groups forming hexagonal tunnels in which are located the La/sup 3 +/ And Sr/sup 2 +/ ions. The slight oxygen substoichiometry with regard to the formulation A/sub 8/Cu/sub 8/O/sub 20/ is discussed in terms of a superstructure along the c axis (c approx. 2a/sub p/), which was observed in some crystals by electron diffraction.« less
  • The new compounds La{sub 6}Ti{sub 2}S{sub 8}O{sub 5} and La{sub 4}Ti{sub 3}S{sub 4}O{sub 8} have been prepared from the reaction of La{sub 2}S{sub 3} with TiO{sub 2}. Both phases are highly resistive and weakly paramagnetic. Single-crystal X-ray diffraction measurements show that La{sub 6}Ti{sub 2}S{sub 8}O{sub 5} crystallizes in space group C{sub 2h}{sup 2}-P2{sub 1}/m of the monoclinic system with two formula units in a cell of dimensions a = 12.572(10), b = 4.053(2), c = 16.289(14) {angstrom}, {beta} = 96.79(1){degrees} (T = 113 K). The structure contains six crystallographically independent La atoms with four different coordination geometries, and Ti atomsmore » in octahedral coordination. The Ti octahedra form an infinite, corner-sharing dimeric chain in the b direction. La{sub 4}Ti{sub 3}S{sub 4}O{sub 8} crystallizes in the monoclinic space group C{sub 2h}{sup 3}-C2/m with four formula units in a cell with dimension a = 18.363(9), b = 3.886(2), c = 17.911(9) {angstrom}, {beta} = 109.83(2){degrees} (T= 113 K). The structure is composed of La atoms in tricapped trigonal prisms and Ti atoms in octahedra and highly distorted tetrahedra. There are four distinct linkages between these octahedra that include edge- and corner-shared O and S atoms.« less