Fig.1 shows the XRD pattern of 0.2BFO + 0.8LNMFO composite.
It is observed from theXRD pattern that the composite confirms the presence of the ferrite andferroelectric phases. The lattice parameter of ferroelectric phase is measuredby solving different sets of three equations corresponding to three consecutivepeaks. Then by taking the average the accurate value of the lattice parameteris obtained. The values of lattice parameter of all the peaks for the ferritephase obtained for each reflected plane are plotted against the Nelson–Rileyfunction 17: , where ? is Bragg’sangle. A straight line has been obtained and the accurate value of the latticeparameter has been determined from the extrapolation of these lines to . Fig.
1: XRD pattern of 0.2BFO + 0.8LNMFO composite sintered at 900 °c.
Fig.2: Variation of Density and Porosity for 0.2BFO + 0.8LNMFO composite.
Fig.2 shows the variation of ?Band P as a function of sintering temperature. The bulk density of the compositeincreases with Ts up to 900°Cthen decreases for further increasing Ts.On the other hand, porosity shows theopposite trend of density as shown in fig. 2.
The increase in ?B with Ts isexpected. This is because during the sintering process, the thermal energygenerates a force that drives the grain boundaries to grow over pores, therebydecreasing the pore volume and denser the material. A further increase of Tsat 9250C, the ?B decreases because the intragranular porosityincrease resulting from the increase of thickness of grain boundary where poresor vacant sites are trapped. 3.2 Microstructure 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 compositesintered at various Ts are shown in Fig. 3. It is noticed that the optimumtemperature of the composite is 900°C.
The average grain size has been calculated by linear intercept technique. The Dis significantly decreases with Ts. The uniformity in the grain sizecan control materials properties such as the magnetic permeability. Thebehavior of grain growth reflects the competition between the driving forcesfor grain boundary movement and the retarding force exerted by pores 18. Whenthe driving force of the grain boundary in each grain is homogeneous, thesintered body attains a uniform grain size distribution; in contrast,discontinuous grain growth occurs if this driving force is inhomogeneous.3.5 DielectricProperties Fig.
7(a) shows thevariation of ?? with frequency at room temperature for 0.2BFO + 0.8LNMFOcomposite. It is observed that the value of ?? decreases rapidly withthe increase in frequency and remain constant at higher frequency. This dielectric dispersion at low frequencyis due to Maxwell–Wagner 27,28 type interfacial polarization in agreementwith Koop’s phenomenological theory 29.
The interfacial polarizationoriginates due to the inhomogeneities of the sample resulting from impurities,porosity, interfacial defects and grain structure. These inhomogeneities aregenerated in the sample during high temperature calcination and sinteringprocesses. At higher frequencies, ?? remains almost frequencyindependent due to the inability of electric dipoles to follow up the fastvariation of the alternating applied electric field 30.