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Title: Structure and physical properties of EuTa{sub 2}O{sub 6} tungsten bronze polymorph

Abstract

A tetragonal tungsten bronze (TTB) polymorph of EuTa{sub 2}O{sub 6} was prepared and analyzed. EuTa{sub 2}O{sub 6} crystallizes in the centrosymmetric Pnam space group (with unit cell: a = 12.3693, b = 12.4254, and c = 7.7228 Å) isomorphous with orthorhombic β-SrTa{sub 2}O{sub 6}. In contrast to early reports, we see no evidence of deviation from paramagnetic Curie-Weiss behavior among the Eu{sup 2+} 4f{sup 7}spins in EuTa{sub 2}O{sub 6} down to 2 K. Dielectric constant shows a broad peak at ca. 50 K with dielectric dispersion resembling diffuse phase transition. The relaxation time, however, follows a simple (non-freezing) thermally activated process with an activation energy of 92 meV and an attempt frequency of f{sub 0} = 5.79 × 10{sup 12 }Hz. A thermal conductivity of EuTa{sub 2}O{sub 6} shows a low-temperature (T ≈ 30 K) “plateau” region reminiscent of a glass-like behaviour in Nb-based TTB compounds. This behaviour can be attributed to the loosely bound Eu{sup 2+} ions occupying large tricapped trigonal prismatic sites in the EuTa{sub 2}O{sub 6} structure.

Authors:
; ; ;  [1]; ;  [2]
  1. National Institute for Materials Science, Tsukuba, Ibaraki 305-0044 (Japan)
  2. Department of Chemistry and Chemical Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S4M1 (Canada)
Publication Date:
OSTI Identifier:
22318009
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 105; Journal Issue: 6; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; DIELECTRIC MATERIALS; EUROPIUM COMPOUNDS; EUROPIUM IONS; NIOBIUM; ORTHORHOMBIC LATTICES; PERMITTIVITY; TANTALATES; THERMAL CONDUCTIVITY; TUNGSTEN BRONZE

Citation Formats

Kolodiazhnyi, T., E-mail: kolodiazhnyi.taras@nims.go.jp, Sakurai, H., Vasylkiv, O., Borodianska, H., Forbes, S., and Mozharivskyj, Y. Structure and physical properties of EuTa{sub 2}O{sub 6} tungsten bronze polymorph. United States: N. p., 2014. Web. doi:10.1063/1.4893011.
Kolodiazhnyi, T., E-mail: kolodiazhnyi.taras@nims.go.jp, Sakurai, H., Vasylkiv, O., Borodianska, H., Forbes, S., & Mozharivskyj, Y. Structure and physical properties of EuTa{sub 2}O{sub 6} tungsten bronze polymorph. United States. doi:10.1063/1.4893011.
Kolodiazhnyi, T., E-mail: kolodiazhnyi.taras@nims.go.jp, Sakurai, H., Vasylkiv, O., Borodianska, H., Forbes, S., and Mozharivskyj, Y. Mon . "Structure and physical properties of EuTa{sub 2}O{sub 6} tungsten bronze polymorph". United States. doi:10.1063/1.4893011.
@article{osti_22318009,
title = {Structure and physical properties of EuTa{sub 2}O{sub 6} tungsten bronze polymorph},
author = {Kolodiazhnyi, T., E-mail: kolodiazhnyi.taras@nims.go.jp and Sakurai, H. and Vasylkiv, O. and Borodianska, H. and Forbes, S. and Mozharivskyj, Y.},
abstractNote = {A tetragonal tungsten bronze (TTB) polymorph of EuTa{sub 2}O{sub 6} was prepared and analyzed. EuTa{sub 2}O{sub 6} crystallizes in the centrosymmetric Pnam space group (with unit cell: a = 12.3693, b = 12.4254, and c = 7.7228 Å) isomorphous with orthorhombic β-SrTa{sub 2}O{sub 6}. In contrast to early reports, we see no evidence of deviation from paramagnetic Curie-Weiss behavior among the Eu{sup 2+} 4f{sup 7}spins in EuTa{sub 2}O{sub 6} down to 2 K. Dielectric constant shows a broad peak at ca. 50 K with dielectric dispersion resembling diffuse phase transition. The relaxation time, however, follows a simple (non-freezing) thermally activated process with an activation energy of 92 meV and an attempt frequency of f{sub 0} = 5.79 × 10{sup 12 }Hz. A thermal conductivity of EuTa{sub 2}O{sub 6} shows a low-temperature (T ≈ 30 K) “plateau” region reminiscent of a glass-like behaviour in Nb-based TTB compounds. This behaviour can be attributed to the loosely bound Eu{sup 2+} ions occupying large tricapped trigonal prismatic sites in the EuTa{sub 2}O{sub 6} structure.},
doi = {10.1063/1.4893011},
journal = {Applied Physics Letters},
number = 6,
volume = 105,
place = {United States},
year = {Mon Aug 11 00:00:00 EDT 2014},
month = {Mon Aug 11 00:00:00 EDT 2014}
}
  • Electrical and magnetic properties of some europium ''tungsten bronze'' type compounds were investigated. Europium was confirmed to be in the + 2 oxidation state. Electrical conductivity in europium niobate Eu Nb/sub 2/O/sub 6/ was found to be much higher than in the tantalate Eu Ta/sub 2/O/sub 6/. The presence of electrons on niobium ions in Eu/sub 0/,/sub 60/ NbO/sub 3/ compound considerably increased the electrical conductivity. Two band models derived from Goodenough's for tungsten bronze structure are discussed.
  • Highlights: • TTB-type SLTN: Ho-Ybx with space group P4/mbm was determined. • UC photoluminescence of SLTN: Ho-Ybx ceramics was first reported. • Bright UC green emission was observed at room temperature. • Two-photon energy transfer process was confirmed for the UC processes. • Temperature stability of dielectric permittivity was improved for SLTN: Ho-Ybx. - Abstract: Ho{sup 3+}- and Yb{sup 3+}-codoped Sr{sub 4}La{sub 2}Ti{sub 4}Nb{sub 6}O{sub 30} (Sr{sub 4}La{sub 1.94–x}Ho{sub 0.06}Yb{sub x}Ti{sub 4}Nb{sub 6}O{sub 30}, abbreviated as SLTN: Ho-Ybx) ceramics have been synthesized, and their structural, up-conversion (UC) photoluminescence, and dielectric properties have been carefully investigated. Through Rietveld structural refinement, SLTN:more » Ho-Ybx samples are determined as single tetragonal tungsten bronze (TTB) phase with space group P4/mbm in which larger Sr{sup 2+} ions fill the A{sub 2}-sites, relative smaller La{sup 3+}, Ho{sup 3+}, and Yb{sup 3+} ions occupy the A{sub 1}-sites, while Ti{sup 4+} and Nb{sup 4+} ions fill the B-sites. Under 980 nm near infrared (NIR) excitation, bright UC green emission, relatively weak red and near-infrared (NIR) emissions, originating from {sup 5}F{sub 4}/{sup 5}S{sub 2} → {sup 5}I{sub 8}, {sup 5}F{sub 5} → {sup 5}I{sub 8}, and {sup 5}F{sub 4}/{sup 5}S{sub 2} → {sup 5}I{sub 7} transitions of Ho{sup 3+} ions, are confirmed for SLTN: Ho-Ybx. Two-photon energy transfer process is proved through pumping laser power dependence of emission intensity measurement. Furthermore, the influence of Ho{sup 3+}- and Yb{sup 3+}- ions on the dielectric properties of SLTN: Ho-Ybx is also investigated and the temperature stability of dielectric permittivity is improved.« less
  • Ba{sub 1-x}RE{sub 2x/3}Nb{sub 2}O{sub 6} nanocrystals with a tetragonal tungsten bronze (TTB) structure are synthesized using a conventional glass crystallization technique in 2.3RE{sub 2}O{sub 3}-27.4BaO-34.3Nb{sub 2}O{sub 5}-36B{sub 2}O{sub 3} (mol%) (RE=Sm, Eu, Gd, Dy, and Er) glasses. One sharp crystallization peak is observed at {approx}670 Degree-Sign C in both powdered and bulk glasses, and the formation of Ba{sub 1-x}RE{sub 2x/3}Nb{sub 2}O{sub 6} nanocrystals with unit cell parameters of a{approx}1.24 nm and c{approx}0.39 nm was confirmed. It is found from high resolution transmission electron microscope observations that the morphology of Ba{sub 1-x}RE{sub 2x/3}Nb{sub 2}O{sub 6} nanocrystals is ellipsoidal. Their average particlemore » size is in the range of 15-60 nm and decreases with decreasing ionic radius of RE{sup 3+} being present in the precursor glasses. The optical transparent crystallized glass (bulk) shows the total photoluminescence (PL) quantum yield of 53% in the visible region of Eu{sup 3+} ions, suggesting a high potential of Ba{sub 1-x}RE{sub 2x/3}Nb{sub 2}O{sub 6} nanocrystals as PL materials. - Graphical abstract: This figure shows a TEM photograph for the heat-treated (667 Degree-Sign C, 3 h) sample of 2.3Dy{sub 2}O{sub 3}-27.4BaO-34.3Nb{sub 2}O{sub 5}-36B{sub 2}O{sub 3}. An ellipsoidal-shaped Ba{sub 1-x}Dy{sub 2x/3}Nb{sub 2}O{sub 6} nanocrystal with diameters of 17 and 28 nm is observed. The ellipsoidal morphology is a common feature in Ba{sub 1-x}RE{sub 2x/3}Nb{sub 2}O{sub 6} nanocrystals synthesized by the crystallization of 2.3RE{sub 2}O{sub 3}-27.4BaO-34.3Nb{sub 2}O{sub 5}-36B{sub 2}O{sub 3} glasses. Highlights: Black-Right-Pointing-Pointer Ba{sub 1-x}RE{sub 2x/3}Nb{sub 2}O{sub 6} nanocrystals with a tetragonal tungsten bronze structure are synthesized. Black-Right-Pointing-Pointer A glass crystallization technique was applied. Black-Right-Pointing-Pointer The morphology of Ba{sub 1-x}RE{sub 2x/3}Nb{sub 2}O{sub 6} nanocrystals is ellipsoidal. Black-Right-Pointing-Pointer The average particle size with 15-60 nm decreases with decreasing ionic radius of RE{sup 3+}. Black-Right-Pointing-Pointer Ba{sub 1-x}RE{sub 2x/3}Nb{sub 2}O{sub 6} nanocrystals have a high potential as photoluminescence materials.« less
  • The dielectrics of Ba{sub 6}Ti{sub 2}Ta{sub 8}O{sub 30} and Sr{sub 6}Ti{sub 2}Ta{sub 8}O{sub 30} were prepared and characterized. These compounds have the tetragonal tungsten-bronze structure and paraelectric nature at room temperature. Very low dielectric loss was determined at 1 MHz in both dielectrics together with a relatively small temperature coefficient. The dielectric constant was 174 and 180 for Ba{sub 6}Ti{sub 2}Ta{sub 8}O{sub 30} and Sr{sub 6}Ti{sub 2}Ta{sub 8}O{sub 30}, respectively.
  • Tetragonal tungsten bronze (TBB) type niobium compounds Sr{sub 6}Nb{sub 10}O{sub 30} and a solid solution series Ba{sub 6{minus}x}La{sub x}Nb{sub 10}O{sub 30} (x = 0, 1, 2, 3) were synthesized and their resistivity was measured in the temperature range 10--300 K. The Sr compound is a semiconductor, the high temperature data (100 {le} T {le} 300 K) for which can be fitted to the T{sup {minus}1/4} law. Ba{sub 6}Nb{sub 10}O{sub 30} also is a semiconductor, but with a different temperature dependency. La-substitution in the Ba compound caused a conduction mechanism to change from semiconducting (x = 0) to metallic (x {ge}more » 1).« less