Ionic and electronic transport in La{sub 2}Ti{sub 2}SiO{sub 9}-based materials

Journal Article · Sun Apr 15 04:00:00 EDT 2007 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2007.01.024· OSTI ID:21015773

Pivak, Y V ^[1]; Naumovich, E N ^[1]; Frade, J R ^[1]; Marques, F M.B. ^[1]

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1. Department of Ceramics and Glass Engineering, CICECO, University of Aveiro, 3810-193 Aveiro (Portugal)

The total conductivity of monoclinic La{sub 2}Ti{sub 2}SiO{sub 9} is mixed oxygen-ionic and n-type electronic, and increases on reduction of the oxygen partial pressure down to 10{sup -21} atm at 973-1223 K. The substitution of Ti{sup 4+} with Nb{sup 5+} decreases both contributions to the conductivity, whilst Pr doping and reducing p(O{sub 2}) have opposite effects. The oxygen ion transference numbers of La{sub 2}Ti{sub 2}SiO{sub 9-} {sub {delta}} , LaPrTi{sub 2}SiO{sub 9{+-}} {sub {delta}} and La{sub 2}Ti{sub 1.8}Nb{sub 0.2}SiO{sub 9{+-}} {sub {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 1.59-1.74 eV, 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{sub 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{sub 2}Ti{sub 2}SiO{sub 9}-based ceramics, calculated from dilatometric data in air, are (8.7-9.5)x10{sup -6} K{sup -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. - Graphical abstract: Structure of mixed-conducting (La,Pr){sub 2}(Ti,Nb){sub 2}SiO{sub 9}.

• OSTI ID: 21015773
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 4 Vol. 180; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ACTIVATION ENERGY
CATIONS
CERAMICS
COMPUTERIZED SIMULATION
ELECTRIC CONDUCTIVITY
EV RANGE 01-10
INTERSTITIALS
IONIC CONDUCTIVITY
LANTHANUM COMPOUNDS
MONOCLINIC LATTICES
NIOBIUM IONS
OXYGEN
OXYGEN IONS
PARTIAL PRESSURE
SILICATES
TEMPERATURE RANGE 0400-1000 K
THERMAL EXPANSION
TITANATES
TITANIUM IONS
VACANCIES