Abstract:
Various polycrystalline Ba1-xSrx(Fe0.5Ta0.5)O3 and Ca1-xSrx(Fe0.5Ta0.5)O3 ceramics (where
x=0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) were prepared by the standard solid state reaction
technique. Powder of ingredients were mixed thoroughly in stoichiometric amount and
calcined at 1150°C for 5 h. Pellet and ring shaped samples prepared from each
composition were sintered at 1400, 1450 and 1500°C for 5 h. The crystalline phase,
microstructure, dielectric properties, ac conductivity, impedance spectroscopy, M-H
hysteresis loop, complex initial permeability and magnetoelectric (ME) coefficient of the
compositions were investigated. X-ray diffraction (XRD) and Field Emission Scanning
Electron Microscopy (FESEM) were used to carry out the structural analysis and surface
morphology, respectively. The XRD analysis confirms that all compositions are single
phase perovskite structure. The lattice parameters of Ba1-xSrx(Fe0.5Ta0.5)O3 decreases with
increasing Sr content. But for the sample Ca1-xSrx(Fe0.5Ta0.5)O3 the lattice parameter
increases with increasing Sr content. The theoretical and bulk density also decreases for
the various Ba1-xSrx(Fe0.5Ta0.5)O3 but for the Ca1-xSrx(Fe0.5Ta0.5)O3 compositions
theoretical and bulk density increases. The average grain size increases for
Ba1-xSrx(Fe0.5Ta0.5)O3 with increasing Sr content up to x=0.1 then decreases with further
increasing Sr content.
The dielectric measurements as a function of frequency and composition were carried out
at room temperature. The dielectric constant ε′ decreases with increasing frequency. This
phenomenon can be explained by the Maxwell-Wagner model. For both compositions the
dielectric constant (ε′) decreases with increasing Sr content. The dielectric loss (tanδ) is
low at lower frequencies but increases with the increase of frequency for all the
compositions. The ac conductivity σac increases with increase of frequency for all the
composition. The complex impedance plot of Z′ Vs Z″ exhibits a tendency of formation
of double semicircular arc. A dominance of grain boundary resistance (Rgb) was observed
for both the compositions. The Rgb increases with increasing Sr content. The maximum
values of saturation and remnant magnetization were determined from M-H hysteresis
loops. For various Ba1-xSrx(Fe0.5Ta0.5)O3 sintered at 1450°C the maximum value of Ms
was found to be 1.9 emu/g for x=0.1. The complex initial permeability was improved
with increasing Sr concentration because of reduced oxygen vacancies which helped to
move the domain wall easily. An enhanced ME coupling was also observed in the studied
samples and the highest values of ME coefficient were found 65 and 42 mV.cm-1Oe-1for
Ca1-xSrx(Fe0.5Ta0.5)O3 and Ba1-xSrx(Fe0.5Ta0.5)O3 ceramics, respectively.
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