Effect of grain boundary and Ar-H-2 atmosphere on electrical conductivity of bulk a-La2Mo2O9 studied by impedance and x-ray photoelectron spectroscopy

The effect of grain boundary on electrical conductivity of alpha-La2Mo2O9 (LAMOX) over the temperature range of 300 degrees C to 400 degrees C has been investigated in this paper. Grain boundary effect characterisation for the mentioned temperature range has been done by electrochemical impedance spectroscopy (EIS). The calculated values of grain boundary width and specific grain boundary conductivity for alpha-La2Mo2O9 are 14.6 nm and 0.0146 mu S/cm respectively. Total ionic conductivity calculated by EIS for alpha-La2Mo2O9 at 300 degrees C is 1 mu S/cm. Resulting electrical conductivity of grain boundary comes out to be two orders less than the total electrical conductivity suggesting high activation energy requirement for grain boundary conduction. The electrical conductivity of alpha-La2Mo2O9 treated in Ar-H-2 atmosphere (2.5 mS cm(-1) at 200 degrees C) is approximately three orders higher than the electrical conductivity of LAMOX treated in air atmosphere. This may be attributed to reduction of Mo6+ to lower valance states in LAMOX as confirmed by x-ray photoelectron spectroscopy (XPS). Therefore, the low ionic conductivity nature of monoclinic phase of La2Mo2O9 has been explained on the basis of grain boundary conduction mechanism in the present study