abstract
The solubility of Ti4+ in the lattice of apatite-type La9.83Si6-xTixO26.75 corresponds to approximately 28% of the Si-site density. The conductivity of La9.83Si6-xTixO26.75 (x = 1-2) is predominantly oxygen-ionic and independent of the oxygen partial pressure in the p(O-2) range from 10(-20) to 0.3 atm. The electron transference numbers determined by the modified faradaic efficiency technique are lower than 0.006 at 900-950 degrees C in air. The open-circuit voltage of oxygen concentration cells with Ti-doped silicate electrolytes is close to the theoretical Nernst value both under oxygen/air and air/10%H-2-90%N-2 gradients at 700-950 degrees C, suggesting the stabilization of Ti4+ in the apatite structure. Titanium addition in La9.83Si6-xTixO26.75 (x = 1-2) leads to decreasing ionic conductivity and increasing activation energies from 93 to 137 U/mol, and enhanced degradation in reducing atmospheres due to SiO volatilization. At p(O-2) = 10(-20) atm and 1223 K, the conductivity decrease after 100h was about 5% for x = 1 and 17% for x = 2. The solubility of Zr4+ in the La9.83Si6-xZrxO26.75 system was found to be negligible, while the maximum concentration of Ce4+ in La9.4-xCexSi6O27-delta is approximately 5% with respect to the number of lanthanum sites. (c) 2006 Elsevier Ltd. All rights reserved.
keywords
OXIDE-ION CONDUCTIVITY; ELECTRICAL-PROPERTIES; ELECTRONIC TRANSPORT; OXYGEN SEPARATION; FUEL-CELLS; TECHNOLOGY; CONDUCTORS; APATITES; DEFECT; YSZ
subject category
Materials Science
authors
Pivak, YV; Kharton, VV; Yaremchenko, AA; Yakovlev, SO; Kovalevsky, AV; Frade, JR; Marques, FMB
our authors
Aleksey Yaremchenko
Principal Researcher
Andrei Kavaleuski
Principal Researcher
Fernando Manuel Bico Marques
Full professor
Jorge Ribeiro Frade
Retired Professor