1 shows the XRD pattern of 0.2BFO + 0.8LNMFO composite. It is observed from the
XRD pattern that the composite confirms the presence of the ferrite and
ferroelectric phases. The lattice parameter of ferroelectric phase is measured
by solving different sets of three equations corresponding to three consecutive
peaks. Then by taking the average the accurate value of the lattice parameter
is obtained. The values of lattice parameter of all the peaks for the ferrite
phase obtained for each reflected plane are plotted against the Nelson–Riley
, where ? is Bragg’s
angle. A straight line has been obtained and the accurate value of the lattice
parameter has been determined from the extrapolation of these lines to
1: XRD pattern of 0.2BFO + 0.8LNMFO composite sintered at 900 °c.
2: Variation of Density and Porosity for 0.2BFO + 0.8LNMFO composite.
2 shows the variation of ?B
and P as a function of sintering temperature. The bulk density of the composite
increases with Ts up to 900°C
then decreases for further increasing Ts.
On the other hand, porosity shows the
opposite trend of density as shown in fig. 2. The increase in ?B with Ts is
expected. This is because during the sintering process, the thermal energy
generates a force that drives the grain boundaries to grow over pores, thereby
decreasing the pore volume and denser the material. A further increase of Ts
at 9250C, the ?B decreases because the intragranular porosity
increase resulting from the increase of thickness of grain boundary where pores
or vacant sites are trapped.
Fig. 3: The FESEM microstructure of 0.2BFO +
0.8LNMFO composite sintered at (a) 850,
(b) 875, (c) 900 and (d) 925 °C.
The FESEM images of 0.2BFO + 0.8LNMFO composite
sintered at various Ts are shown in Fig. 3. It is noticed that the optimum
temperature of the composite is 900°C.
The average grain size has been calculated by linear intercept technique. The D
is significantly decreases with Ts. The uniformity in the grain size
can control materials properties such as the magnetic permeability. The
behavior of grain growth reflects the competition between the driving forces
for grain boundary movement and the retarding force exerted by pores 18. When
the driving force of the grain boundary in each grain is homogeneous, the
sintered body attains a uniform grain size distribution; in contrast,
discontinuous grain growth occurs if this driving force is inhomogeneous.
Fig. 7(a) shows the
variation of ?? with frequency at room temperature for 0.2BFO + 0.8LNMFO
composite. It is observed that the value of ?? decreases rapidly with
the increase in frequency and remain constant at higher frequency. This dielectric dispersion at low frequency
is due to Maxwell–Wagner 27,28 type interfacial polarization in agreement
with Koop’s phenomenological theory 29. The interfacial polarization
originates due to the inhomogeneities of the sample resulting from impurities,
porosity, interfacial defects and grain structure. These inhomogeneities are
generated in the sample during high temperature calcination and sintering
processes. At higher frequencies, ?? remains almost frequency
independent due to the inability of electric dipoles to follow up the fast
variation of the alternating applied electric field 30.