The molar heat capacities of La2Mo209 and La1.9Sr0.1MO209-δ were obtained using the differential scanning calorimetry （DSC） technique in a temperature range from 298 to 1473 K. The DSC curve of La2Mo209 showed an endothermal peak around 834 K corresponding to a first-order monoclinic-cubic phase transition, and the enthalpy change accompanying this phase transition is 5.99 kJ/mol. No evident endothermal peak existed in the DSC curve of La1.9Sr0.1MO209-δ, but a broad thermal anomaly existed in its heat capacity curve at around 832 K. In addition, the heat capacity values of La2Mo209 and La1.9Sr0.1MO209-δ began to decrease at 1196 and 1330 K, respectively. The non-transitional heat capacity values of La2Mo209 and La1.9Sr0.1MO209-δ were formulated using multiple regression analysis in two temperature ranges.
Baijun Yan Jianhua Liu Yunduo Dai Qifeng Shu Zhihua Ren
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 La2-xSrxM02O9 -δ was in the range of 7 mol.% to 7.5 tool.%, i.e., the maximum stoichiometric coefficient x in La2~SrxMo209_a was larger than 0.14 and less than 0.15. The cubic lattice parameter of La2 xSrxM02Og-δ （0〈x〈4） increased linearly with the content of dopant Sr2＋ increasing and the relationship could be expressed as： a=0.7154＋0.0045 lx （ram）. The total conductivities of Sr-doped La2M0209 were measured by im- pedance spectroscopy method in argon and air atmosphere, respectively. The results indicated that substituting Sr2＋ fbr La3＋ could suppress the first order phase transform ofLa2M02O9 and stabilize the cubic structure to room temperature, and tile conductivities of Sr-doped La2M02O9 were more sensitive to the change of atmosphere than that of undoped La2M02O9. The conductivity variation of Sr-doped La2M02O9 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 La2M02O9 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 St-doped La2Mo2O9 samples could also reach 0.99.
Single-phase La_（2–x）Nd_xMo_2O_9（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 Nb^（3＋） in La_（2–x）Nd_xMo_2O_9 was determined to be in the range of 1.8
