Ionic and electronic transport in La(2)Ti(2)SiO(9)-based materials
authors Pivak, YV; Kharton, VV; Naumovich, EN; Frade, JR; Marques, FMB
nationality International
journal JOURNAL OF SOLID STATE CHEMISTRY
author keywords lanthanum titanate-silicatc; oxygen ionic conductivity; n-type electronic transport; ion transference number; thermal expansion; atomistic computer simulations
keywords OXIDE FUEL-CELLS; CRYSTAL-STRUCTURE; CONDUCTORS; CONDUCTIVITY; DEFECT; TECHNOLOGY; STABILITY; MIGRATION; ND; SM
abstract The total conductivity of monoclinic La(2)Ti(2)SiO(9) is mixed oxygen-ionic and n-type electronic, and increases on reduction of the oxygen partial pressure down to 10(-21) atm at 973-1223 K. The Substitution of Ti(4+) with Nb(5+) decreases both contributions to the conductivity, whilst Pr doping and reducing p(O(2)) have opposite effects. The oxygen ion transference numbers of La)Ti(2)SiO(9-delta),5, LaPrTi(2)SiO(9 +/-delta) and La(2)Ti(1.8)Nb(0.2)SiO(9+delta) ceramics, measured by the faradaic efficiency and e.m.f. methods, vary in the range 0.15-0.32, increasing when temperature decreases. In air, the activation energies for the ionic and electronic transport are 1.23-1.40 and 1.59-1.74eV, respectively. Protonic contribution to the conductivity in wet atmospheres becomes significant at temperatures below 1000 K. The experimental data and the results of atomistic computer Simulations suggest that the oxygen-ionic and electronic transport is primarily determined by processes involving TiO(6) octahedra. The ionic conduction may occur via both the vacancy and interstitial migration mechanisms, but the former is more favorable energetically and should dominate, at least, in reducing atmospheres. The average thermal expansion coefficients of La(2)Ti(2)SiO(9)-based ceramics, calculated from dilatometric data in air, are (8.7-9.5) x 10(-6) K(-1) at 300-1373 K. The lattice of lanthanum titanate-silicate is almost intolerant with respect to A-site deficiency and to doping with lower-valence cations, such as Sr and Fe. (C) 2007 Elsevier Inc. All rights reserved.
publisher ACADEMIC PRESS INC ELSEVIER SCIENCE
issn 0022-4596
year published 2007
volume 180
issue 4
beginning page 1259
ending page 1271
digital object identifier (doi) 10.1016/j.jssc.2007.01.024
web of science category Chemistry, Inorganic & Nuclear; Chemistry, Physical
subject category Chemistry
unique article identifier WOS:000246323400014
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journal impact factor 2.179
5 year journal impact factor 2.130
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