Neutron diffraction investigation of the evolution of the crystal structure of oxygen-conducting solid solutions (Yb{sub 1-x}Ca{sub x}){sub 2}Ti{sub 2}O{sub 7} (x = 0, 0.05, 0.10)

Journal Article · Thu Jan 15 04:00:00 EST 2009 · Crystallography Reports

DOI:https://doi.org/10.1134/S1063774509010052· OSTI ID:22050880

Sokolov, A E; Ul'yanov, V A; Trunov, V A ^[1]; Boguslavskii, M V ^[2]; Levchenko, A V ^[3]; Shcherbakova, L G ^[2]

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1. Russian Academy of Sciences, Konstantinov Institute of Nuclear Physics (Russian Federation)
2. Russian Academy of Sciences, Semenov Institute of Chemical Physics (Russian Federation)
3. Russian Academy of Sciences, Institute of Problems of Chemical Physics (Russian Federation)

The crystal structure of pyrochlore-like solid solutions (Yb{sub 1-x}Ca{sub x}){sub 2}Ti{sub 2}O{sub 7} (x = 0, 0.05, 0.10) synthesized by high-temperature annealing of mechanically activated initial oxides at temperatures of 1300-1500 deg. C is studied using neutron diffraction. It is found that the Ca{sup 2+} cations are located in the ytterbium sublattice, which apparently favors the splitting of one of the oxygen sublattices [O(2) (48f)] of the pyrochlore structure: the decrease in the occupancy of this sublattice is accompanied by the formation of a new sublattice O(3) (8b), whereas the other oxygen sublattice O(1) (8a) remains unchanged. This rearrangement of the anions in the oxygen subsystem due to the incorporation of an alkaline-earth cation explains the high ionic conductance ({approx}0.2 S/cm at 1000 deg. C) for (Yb{sub 0.9}Ca{sub 0.1}){sub 2}Ti{sub 2}O{sub 7} {approx} 0.2, which is the maximum value observed to date for pyrochlores of the A{sub 2}B{sub 2}O{sub 7} type, where A = Ln and B is a Subgroup IVA element of the periodic system. The bulk and grain-boundary components of the conductivity of (Yb{sub 0.95}Ca{sub 0.05}){sub 2}Ti{sub 2}O{sub 7} synthesized at temperatures of 1300, 1400, and 1500 deg. C are studied using impedance spectroscopy. It is found that the (Yb{sub 0.95}Ca{sub 0.05}){sub 2}Ti{sub 2}O{sub 7} sample synthesized at 1500 deg. C has the highest total conductivity due to the increased grain-boundary component. The bulk component of the ionic conductivity of (Yb{sub 0.95}Ca{sub 0.05}){sub 2}Ti{sub 2}O{sub 7} is hardly affected by the synthesis temperature and depends mainly on the degree of heterovalent substitution.

• OSTI ID: 22050880
• Journal Information: Crystallography Reports, Journal Name: Crystallography Reports Journal Issue: 1 Vol. 54; ISSN 1063-7745; ISSN CYSTE3
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ANNEALING
CALCIUM COMPOUNDS
CALCIUM IONS
CRYSTAL STRUCTURE
GRAIN BOUNDARIES
IMPEDANCE
IONIC CONDUCTIVITY
NEUTRON DIFFRACTION
PYROCHLORE
SOLID SOLUTIONS
SPECTROSCOPY
SYNTHESIS
TEMPERATURE RANGE 1000-4000 K
TITANATES
YTTERBIUM COMPOUNDS