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 varioustemperatures. 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
x
constant improved with the rise in the time of heat treatment. This
increase in crystallinity shows higher value of dielectric constant.
