Synthesis of LaFeO3 by Carbon Containing and Carbon free Precursors and Characterization

Abstract

In this work, Auto-combustion method and co-precipitation method is used to prepare LaFeO3. The Nano powder was successfully synthesized using chelating agent, precipitating agent and nitrates of iron and lanthanum. To explore the thermal growth of the crystalline phases, the as burnt sample and dry precipitates were kept in a furnace at 450oC, 600oC, 800oC and at 1000oC (in co-precipitation method) for four hours at each temperature. X-ray diffraction technique revealed that at temperature 450oC only the Fe (OH)3 and La (OH)3 were present there in powder dominantly in amorphous form. Increasing the treatment temperature caused the decomposition of these hydroxides into Fe2O3 and La2O3 accompanied by the formation of LaFeO3. The formation of LaFeO3 incomplete up to 800oC in Co-precipitation method and found crystalline LaFeO3 in combustion method at same temperature. LaFeO3 was obtained at 1000°C indicating that heating at 1000oC changes it into complete transformation of the oxides and hydroxides (of Fe and La) to LaFeO3 in co-precipitation method. For the sake of exploring the effect of variations in microstructure of samples prepared by precipitation method, the powder treated at 1000°C was pressed into several pellets of circular shape having the diameter of 10 mm and 1 mm thickness. The sintering temperature of the pellets was 1000oC selectively for 4, 8, 12 and 16 hours and were named as LF4, LF8, LF12 and LF16, respectively. Scanning electron microscopy (SEM) revealed that the particles possess spherical symmetry. The average grain size of LaFeO3 was found 200 nm and the grain size continue to grow by increasing the treatment time. The stability of carbonate residual precursors in combustion method has been explored by TGA. FTIR analysis of both method’s samples was done after treatment of heat at various temperatures. During heat treatment the continuous decomposition of these residuals occurred. The room temperature dielectric properties of LaFeO3 were analyzed and examined thoroughly at frequencies from 1 Hz to 10 MHz of both method’s samples and explored the effect of residual carbonate precursors on dielectric properties of combusted samples. The dielectric properties of combusted samples strongly affected by these amorphous carbonate residues. It was found that the value of dielectric constant improved wi th the rise in the t ime of heat t reatment . This increase in cryst al l ini ty shows higher value of di el ect ri c const ant .