Oxygen ionic and electronic transport in apatite-type La10-x(Si,Al)(6)O-26 +/-delta
authors Shaula, AL; Kharton, VV; Marques, FMB
nationality International
journal JOURNAL OF SOLID STATE CHEMISTRY
author keywords lanthanum silicate; apatite; solid oxide electrolyte; oxygen ionic conductivity; electronic transport; faradaic efficiency; ion transference number; thermal expansion; Seebeck coefficient
keywords FORMER SOVIET-UNION; OXIDE FUEL-CELLS; ELECTRICAL-PROPERTIES; SOLID ELECTROLYTES; SINGLE-CRYSTALS; CONDUCTIVITY; CONDUCTORS; PHASES; DEFECT; PR
abstract The main factor governing the oxygen ionic conductivity in apatite-type La10-xSi6-yAlyO27-3O27-3x/2-y/2 = (x = 0-0.33; y = 0.5- 1.5) is the concentration of mobile interstitials determined by the total oxygen content. The ion transference numbers, measured by modified faradaic efficiency technique., vary in the range 0.9949-0.9997 in air and increase on reducing oxygen partial pressure due to decreasing p-type electronic conduction. The activation energies for ionic and hole transport are (56-67)+/- 3kJ/mol and (57-100)+/- 8 kJ/mol, respectively. Increasing oxygen content leads to hi-her hole conduction in oxidizing atmospheres and promotes minor oxygen losses from the lattice when the oxygen pressure decreases, although the overall level of ionic conductivity is almost constant in the p(O-2) range from 50 kPa down to 10(-16) Pa. Under reducing conditions at temperatures above 1100 K. silicon oxide volatilization from the surface layers of apatite ceramics results in a moderate decrease of the conductivity with time. This suggests that the operation of electrochemical cells with silicate-based solid electrolytes should be limited to the intermediate-temperature range, such Lis 800-1000 K, where the ionic transport in most-conductive apatite phases containing 26.50-26.75 oxygen atoms per unit formula is higher than that in stabilized zirconia. The average thermal expansion coefficients of apatite ceramics, calculated from dilatometric data in air, are (8.7-10.8) x 10(-6) K-1 at 300-1300 K. (c) 2005 Elsevier Inc. All rights reserved.
publisher ACADEMIC PRESS INC ELSEVIER SCIENCE
issn 0022-4596
year published 2005
volume 178
issue 6
beginning page 2050
ending page 2061
digital object identifier (doi) 10.1016/j.jssc.2005.04.018
web of science category Chemistry, Inorganic & Nuclear; Chemistry, Physical
subject category Chemistry
unique article identifier WOS:000229753200041
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journal impact factor 2.726
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