Transport properties and Moessbauer spectra of Fe-substituted La{sub 10-x}(Si,Al){sub 6}O{sub 26} apatites
Increasing iron content in apatite-type La{sub 9.83}Si{sub 4.5}Al{sub 1.5-y}Fe{sub y}O{sub 26+{delta}} (y=0.5-1.5) leads to increasing unit cell volume, fraction of Fe{sup 4+}, partial oxygen ionic and p-type electronic conductivities, and ceramics sinterability. The oxygen ion transference numbers, determined by Faradaic efficiency (FE) measurements at 973-1223 K in air, are in the range 0.986-0.994. Data on total conductivity and Seebeck coefficient as functions of the oxygen partial pressure, varying in the range 10{sup -2} Pa to 70 kPa, confirm that under oxidizing conditions the ionic conduction in Fe-substituted La{sub 9.83}(Si,Al){sub 6}O{sub 26+{delta}} apatites is dominant. Due to stabilization of Fe{sup 3+}, substantially worse transport properties are observed for A-site stoichiometric La{sub 10}Si{sub 4}Fe{sub 2}O{sub 26}, having activation energy for ionic conductivity of 107 kJ/mol and electron transference numbers close to 0.03. The correlation between partial ionic and electron-hole conductivities suggests a significant role of Fe{sup 4+} formation compensated by extra oxygen incorporation into the vacant sites, which are formed due to Frenkel-type disorder induced by La vacancies. The average thermal expansion coefficients of Fe-doped La{sub 10-x}(Si,Al){sub 6}O{sub 26+{delta}} ceramics, calculated from dilatometric data in air, are 8.9x10{sup -6} to 9.9x10{sup -6} K{sup -1} at 300-1250 K.
- OSTI ID:
- 20888054
- Journal Information:
- Materials Research Bulletin, Vol. 39, Issue 6; Other Information: DOI: 10.1016/j.materresbull.2004.02.010; PII: S0025540804000339; Copyright (c) 2004 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0025-5408
- Country of Publication:
- United States
- Language:
- English
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