Structural and electrical properties of La2-xSrxMo2O9-δ

Sr-doped La₂Mo₂O₉ were prepared by solid state reaction and characterized by XRD, impedance spectroscopy and Hebb- Wagner polarization method. XRD patterns of the samples indicated that the solubility limit of Sr²⁺ in La_2–xSr_xMo₂O_9–δ was in the range of 7 mol.% to 7.5 mol.%, i.e., the maximum stoichiometric coefficient x in La_2–xSr_xMo₂O_9–δ was larger than 0.14 and less than 0.15. The cubic lattice parameter of La_2–xSr_xMo₂O_9–δ (0<x≤0.14) increased linearly with the content of dopant Sr²⁺ increasing and the relationship could be expressed as: a=0.7154+0.00451x (mm). The total conductivities of Sr-doped La₂Mo₂O₉ were measured by impedance spectroscopy method in argon and air atmosphere, respectively. The results indicated that substituting Sr²⁺ for La³⁺ could suppress the first order phase transform of La₂Mo₂O₉ and stabilize the cubic structure to room temperature, and the conductivities of Sr-doped La₂Mo₂O₉ were more sensitive to the change of atmosphere than that of undoped La₂Mo₂O₉. The conductivity variation of Sr-doped La₂Mo₂O₉ with the dopant content exhibited similar trend in air and argon atmosphere, firstly decreased and then increased with the dopant content increasing, and a minimum value appeared at x=0.1. The electronic conductivities of Sr-doped La₂Mo₂O₉ were measured using Hebb-Wagner polarization method in argon atmosphere. It could be found that Sr-doping caused the increase in electronic conductivity and decrease in oxide-ion transport numbers, but the conducting species were predominantly oxide ions. And the oxide-ion transport numbers of some Sr-doped La₂Mo₂O₉ samples could also reach 0.99.