Phase transformation, thermal expansion and electrical conductivity of lanthanum chromite

This paper addresses discrepancies pertaining to structural, thermal and electrical properties of lanthanum chromite. Experimental evidence is provided to support the hypothesis for poor densification in air as well as reduction in electrical conductivity in reducing atmosphere. Sintering condition for the synthesis of LaCrO3 was optimized to 1450 degrees C and 10 h. Thermo-analytical (differential scanning calorimetry - DSC) and high temperature X-ray diffraction (HT-XRD) studies show that orthorhombic lanthanum chromite transforms into rhombohedral structure at similar to 260 degrees C and cubic structure above 1000 degrees C. Co-existence of the structural phases and the variation in each polymorph with temperature in both air and 3%H-2-Ar atmosphere is reported. Presence and absence of Cr-rich phase at inter-particle neck are observed in oxidizing and reducing atmospheres respectively. The linear thermal expansion coefficient was calculated to be 10.8 +/- 0.2 x 10(-6) degrees C-1 in the temperature range of RT-1400 degrees C. Electrical conductivity of lanthanum chromite was found to be 0.11 S/cm in air. A decrease in electrical conductivity (0.02 S/cm at 800 degrees C) of LaCrO3, as observed in reducing atmosphere (3%H-2-Ar), corresponds to lattice volume change as indicated by peak shift in HT-XRD results. (C) 2013 Elsevier Ltd. All rights reserved.