Stability and transport properties of La2Mo2O9
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La2Mo2O9 samples were prepared from freeze-dried powder precursors and characterized by XRD, TG/DTA, SEM, electrical and electrochemical measurements. Pellets with different density were obtained by sintering at temperatures between 900 and 1100 °C to obtain nearly dense samples with grain sizes in the range 1–8 μm. The electrical conductivity was measured using impedance spectroscopy. The capacitance and relaxation frequencies of the main contributions to the spectra were used to ascribe the contributions of grain interiors and internal interfaces, and their temperature dependence. A coulometric titration technique was used to evaluate the change of oxygen stoichiometry under moderately reducing conditions, and to estimate the stability limits under strongly reducing conditions. An ion-blocking method was used to evaluate the onset of n-type conductivity, and a combination of these results with total conductivity measurements was used to obtain the ionic transport number. A combination of oxygen stoichiometry changes and ion-blocking results was used to obtain estimates of mobility.
KeywordsCoulometric titration Freeze-dried precursor Ion blocking Lanthanum molybdenum oxide Phase transition
The authors acknowledge financial support by the Spanish Research Program MCyT (MAT-2001-3334); by the Canary Islands Government (COFI 2002/027); by FCT, Portugal, under contract POCTI/CTM/39381/2001; and by “Accion Integrada” HP01-82. Also, we wish to thank “Convenio Cajacanarias-ULL” for a grant (D.M.L.) and M.E.C.D. for a F.P.U. grant (D.P.C.).
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