Microstructural and high-temperature electrical characterization of La1-xSrxFeO3-δ

Strontium-doped lanthanum ferrites (LSF) were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), 4-point D.C. electrical conductivity and bulk property measurements. The results were compared to those of previous studies as well as selected processing conditions. The investigation focused on effects of sintering temperature, time, atmosphere (air, O-2 and N-2) and composition of La1-xSrxFeO3-delta (x = 0.2-0.9), on the sintering behavior, microstructural development and electrical conductivity. An oxalate precipitation method was used to prepare lanthanum ferrite powders. Simultaneous thermogravimetric and differential thermal analysis (TGA/DTA) studies found calcination temperatures of 800 and 850 degrees C were necessary to form single-phase crystalline powders, as determined by XRD. Specimens were sintered from 1300 to 1400 degrees C with dwell times from 1/2 to 2 hrs. Results from SEM/EDS analysis showed the presence of a second phase in the samples fired in air or oxygen. The second phase was not detected by x-ray diffraction due to the small amount of material present. Samples fired in nitrogen had the lowest conductivity while those fired in oxygen had the highest. A composition of x = 0.5 resulted in the highest conductivity, 352 S/cm, at an operating temperature of 550 degrees C in air. High strontium additions (x = 0.9) lowered the linear shrinkage of LSF.