Thermal and transport properties of La_2–xNd_xMo₂O₉

闫柏军¹，任志华^1,2，侯新梅¹

1. Department of Physical Chemistry of Metallurgy, University of Science and Technology Beijing2. School of Chemical Engineering,Qingdao University of Science and Technology

摘 要：Single-phase La_2–xNd_xMo₂O₉（0≤x≤1.8） compounds were prepared using solid-state reaction technique. Their structural and thermal p roperties were characterized by room and high temperatures X-ray diffraction（XRD）, thermo gravimetric analysis-differential scanningcalorimetry（TG-DSC）, and high temperature Raman spectra. The transport properties were investigated using D.C. four-probe technique and Hebb-Wagner polarization method. The substitution limit of Nb³⁺ in La_2–xNd_xMo₂O₉ was determined to be in the range of 1.8<x<1.9, and the cubic lattice parameter of La_2–xNd_xMo₂O₉ decreased linearly with the increasing of x. When the Nb³⁺ substitution content x was larger than 0.6, the α/β phase transition could be depressed to such a great degree that the phase transition thermal enthalpy was not detected by DSC. The temperature dependence of electrical conductivities for La_1.4Nd_xMo₂O₉ below 873 K and that for LaNdMo₂O₉ below 923 K obeyed the Arrhenius law, while above 873 and 923 K Vogel-Tammann-Fulcher（VTF） model could describe the conduction behaviors satisfactorily. The transition of transport mechanism from Arrhenius to VTF was caused by the change of structure, which was supported by the high temperature XRD and Raman results. The ionic transport number of La_1.4Nd_xMo₂O₉ in air was larger than 0.99 at 1073 K, and with the increasing of temperature it was close to 0.98 at 1173 K. In view of the phase transition, thermal expansion and conductivity properties, La_1.4Nd_xMo₂O₉ should be a promising electrolyte material in La_2–xNd_xMo₂O₉ series.

关键词：