Topological metastability and oxide ionic conduction in La(2)-(x)Eu(x)Mo(2)O(9).
The effect of partial substitution, up to x = 0.4, of La by trivalent Eu on the phase stability, thermal expansion, and transport properties of La2Mo2O9 are investigated using temperature-controlled X-ray powder diffraction, differential thermal analysis, and complex impedance spectroscopy. At low europium content (x < or = 0.1), the alpha-beta phase transition is observed at a temperature dependent on the sample shaping (powder, pellet, etc.). At high europium content (x > or = 0.25), the samples remain cubic (beta phase), regardless of the shaping. In the intermediate range of europium content (x = 0.15, 0.2), the phase stability is highly sensitive to the thermal history and the sample shaping, with a double-reversed beta-alpha-beta transition suppressed by the shaping/sintering process. The influence of the amount of europium on the transport mechanisms and parameters is studied in both low- (Arrhenius) and high-temperature (Vogel-Tammann-Fulcher = VTF) regimes. If the effect of substitution is rather mild and monotonous within each transport regime and crystallographic phase, an abrupt change in the Arrhenius parameters between the alpha- and beta-type phases is observed.
Corbel
Gwenaël
G
Laboratoire des Oxydes et Fluorures, UMR-6010 CNRS, Université du Maine, Avenue Olivier Messiaen, Le Mans Cedex 9, France. gwenael.corbel@univ-lemans.fr
Chevereau
Elodie
E
Kodjikian
Stéphanie
S
Lacorre
Philippe
P