Abstract

• Perovskite based transition metal oxides has been focused since the last few decades because of its wide range of applications in the environmental catalyst, gas sensors, oxygen permeation membranes, electrode materials in solid oxide fuel cells (SOFCs) etc. The aim of the research work is to study the structural, optical and electrical properties of perovskite type LaCoO3 and LaFeO3. These nanocrystalline powders were synthesized by citrate sol-gel method by using metal nitrates as starting materials and citric acid as the chelating agent. The dried precursor powders of LaCoO3 and LaFeO3 were amorphous and their thermal decomposition occurs stepwise upon heating to 600 .C by TG-DTA analysis. Pure perovskite type single phase LaCoO3 and LaFeO3 powders are formed after heating at 450 .C. The pellets prepared from calcined powders were sintered at 800, 900 and 1000 .C and crystalline pellets were characterized by XRD, FT IR, EDXRF, SEM, UV-Visible spectrometer and LCR meter. The XRD data confirms that the LaCoO3 has hexagonal structure with space group R3c and LaFeO3 has orthorhombic structure with space group Pnma. SEM micrograph shows that nanostructure and EDXRF analysis confirms that the all elements of the sample were present in good agreements with stoichiometric ratio. The optical properties of LaCoO3 and LaFeO3 were studied from UV-Visible spectrophotometer and the optical band gaps were also estimated by using Tauc’s relation. The band gap values of these samples are 2.10eV and 2.40 eV respectively and these values are lie within semiconductor band-gap range. Frequency dependence of dielectric behaviour of the two perovskite samples was examined by LCR meter within the frequency range of 100 kHz- 1000 kHz. Dielectric loss tangent and dielectric loss were found to decrease with increase of frequency. The ac conductivity was dependent on the dielectric nature of the prepared samples and it was gradually increased with increase of frequency. The resistivity of LaCoO3 sample is lower than that of LaFeO3 sample. The dc and ac conductivities of LaCoO3 are higher than that of the LaFeO3 sample.