Corbel Gwenaël, Chevereau Elodie, Kodjikian Stéphanie, Lacorre Philippe
Laboratoire des Oxydes et Fluorures, UMR-6010 CNRS, Université du Maine, Avenue Olivier Messiaen, Le Mans Cedex 9, France.
Inorg Chem. 2007 Aug 6;46(16):6395-404. doi: 10.1021/ic700876d. Epub 2007 Jul 4.
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.
采用温控X射线粉末衍射、差热分析和复阻抗谱研究了用三价铕部分替代镧（替代量高达x = 0.4）对La2Mo2O9的相稳定性、热膨胀和输运性质的影响。在低铕含量（x≤0.1）时，观察到α-β相变温度取决于样品成型方式（粉末、颗粒等）。在高铕含量（x≥0.25）时，无论成型方式如何，样品均保持立方相（β相）。在铕含量的中间范围（x = 0.15、0.2），相稳定性对热历史和样品成型高度敏感，成型/烧结过程抑制了双反向β-α-β转变。在低温（阿仑尼乌斯）和高温（沃格尔-塔曼-富尔彻=VTF）区域研究了铕含量对输运机制和参数的影响。如果在每个输运区域和晶体相内替代效应相当温和且单调，则在α型和β型相之间观察到阿仑尼乌斯参数的突然变化。
