Study of the structural and multiferroic properties of D1-xSrx(Fe0.5Ta0.5)O3 [D=Ba and Ca] ceramics

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. I