Conventional solid state reaction technique was used to synthesize Ca1-xSrx(Fe0.5Ta0.5)O3 multiferroic ceramics (where x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5). Powder of ingredients was mixed thoroughly in stoichiometric...Conventional solid state reaction technique was used to synthesize Ca1-xSrx(Fe0.5Ta0.5)O3 multiferroic ceramics (where x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5). Powder of ingredients was mixed thoroughly in stoichiometric amount and calcined at 1150°C for 5 h. Disk and toroid shaped samples prepared from each composition were sintered at 1450°C for 5 h. The XRD analysis confirms that all compositions are single phase cubic perovskite structure. The theoretical and bulk density increases with increase of Sr content, which may be attributed to the fact that the atomic weight and density of Sr are larger than those of Ca. The average grain size increased with increasing Sr content up to x = 0.2, and then decreased with further increase of Sr content. Frequency dependent dielectric constant shows usual dielectric dispersion at lower frequencies due to Maxwell-Wagner type interfacial polarization. The higher values of real and imaginary part of impedance at lower frequencies are also due to the fact that all kinds of polarization mechanism are present and increase with Sr content indicating the enhancement property of the composition. The continuous dispersion on increasing frequency contributes to the conduction phenomena. Two semicircles correspond to the grain boundary and grain resistance separately. The complex modulus analysis reveals the polaron hopping and negligibly small contribution of electrode effect. The continuous dispersion on increasing frequency may be contributed to the conduction phenomena. The ac conductivity, σac, was derived from the dielectric measurement and it increases with increase of frequency for all the compositions and can also be explained on the basis of polaron hopping mechanism. At higher frequencies conductive grains are more active, and thereby increases of hopping of charge carrier contribute to rise in conductivity. The real part of initial permeability increased with increasing Sr content up to x = 0.2, and then decreased further increasing the Sr content. Firstly, it increased due to the higher values of grain size, and then decreased with the Sr content due to the lowering the grain size. The saturation magnetization, Ms, increases for x = 0.2 and then decreases with increasing Sr content due to the pore acted as a pinning centre of electron spin;thereby Ms decreases also due to the grain size which is well supported by the permeability results. The decrease of magnetoelectric voltage coefficient αME with content may be attributed to the increased porosity in the sample. The presence of the pores breaks the magnetic contacts between the grains. The highest value of αME is 42.22 mV·cm-1·Oe-1 for the composition x = 0.2 which is attributed to the enhanced mechanical coupling. It was revealed that there is a dramatic influence of Sr with content x = 0.2 and also has strong correlations on grain size as well as magnetic and magnetoelectric properties.展开更多
Frequency-dependent dielectric constant,dielectric loss,AC conductivity values and complex impedance spectra of V_(2)O_(5)-added Ni-Co-Zn ferrites(Ni_(0.62)Co_(0.03)Zn_(0.35)Fe_(2)O_(4)+xV_(2)O_(5),where x=0,0.5,1 and...Frequency-dependent dielectric constant,dielectric loss,AC conductivity values and complex impedance spectra of V_(2)O_(5)-added Ni-Co-Zn ferrites(Ni_(0.62)Co_(0.03)Zn_(0.35)Fe_(2)O_(4)+xV_(2)O_(5),where x=0,0.5,1 and 1.5 wt.%)have been investigated at room tempera-ture.The dielectric properties of the samples follow the Maxwell-Wagner polarization model.An inverse relationship was found between dielectric constant and AC electrical resistivity for all the samples.The dielectric constants decreased with the addition of V_(2)O_(5),while the electrical resistivities of V_(2)O_(5)-added Ni-Co-Zn ferrites are found to be larger than that of pure Ni-Co-Zn ferrite.The AC conductivity was reduced with the addition of V_(2)O_(5)to Ni-Co-Zn ferrite at lower-frequency region.However,AC conductivity shows a sharp increase at higher-frequency region,which could be attributed to the enhancement of electron hopping between the Fe2+and Fe3+ions in the ferrite matrix due to the activity of the grains.The complex impedance spectroscopy results through Cole-Cole/Nyquist plot have demonstrated a single semicircular arc.It indicates that conduction mechanism takes place predominantly through the grain/bulk property,which could be ascribed to the larger grain size of V_(2)O_(5)-added Ni-Co-Zn ferrites.展开更多
文摘Conventional solid state reaction technique was used to synthesize Ca1-xSrx(Fe0.5Ta0.5)O3 multiferroic ceramics (where x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5). Powder of ingredients was mixed thoroughly in stoichiometric amount and calcined at 1150°C for 5 h. Disk and toroid shaped samples prepared from each composition were sintered at 1450°C for 5 h. The XRD analysis confirms that all compositions are single phase cubic perovskite structure. The theoretical and bulk density increases with increase of Sr content, which may be attributed to the fact that the atomic weight and density of Sr are larger than those of Ca. The average grain size increased with increasing Sr content up to x = 0.2, and then decreased with further increase of Sr content. Frequency dependent dielectric constant shows usual dielectric dispersion at lower frequencies due to Maxwell-Wagner type interfacial polarization. The higher values of real and imaginary part of impedance at lower frequencies are also due to the fact that all kinds of polarization mechanism are present and increase with Sr content indicating the enhancement property of the composition. The continuous dispersion on increasing frequency contributes to the conduction phenomena. Two semicircles correspond to the grain boundary and grain resistance separately. The complex modulus analysis reveals the polaron hopping and negligibly small contribution of electrode effect. The continuous dispersion on increasing frequency may be contributed to the conduction phenomena. The ac conductivity, σac, was derived from the dielectric measurement and it increases with increase of frequency for all the compositions and can also be explained on the basis of polaron hopping mechanism. At higher frequencies conductive grains are more active, and thereby increases of hopping of charge carrier contribute to rise in conductivity. The real part of initial permeability increased with increasing Sr content up to x = 0.2, and then decreased further increasing the Sr content. Firstly, it increased due to the higher values of grain size, and then decreased with the Sr content due to the lowering the grain size. The saturation magnetization, Ms, increases for x = 0.2 and then decreases with increasing Sr content due to the pore acted as a pinning centre of electron spin;thereby Ms decreases also due to the grain size which is well supported by the permeability results. The decrease of magnetoelectric voltage coefficient αME with content may be attributed to the increased porosity in the sample. The presence of the pores breaks the magnetic contacts between the grains. The highest value of αME is 42.22 mV·cm-1·Oe-1 for the composition x = 0.2 which is attributed to the enhanced mechanical coupling. It was revealed that there is a dramatic influence of Sr with content x = 0.2 and also has strong correlations on grain size as well as magnetic and magnetoelectric properties.
文摘Frequency-dependent dielectric constant,dielectric loss,AC conductivity values and complex impedance spectra of V_(2)O_(5)-added Ni-Co-Zn ferrites(Ni_(0.62)Co_(0.03)Zn_(0.35)Fe_(2)O_(4)+xV_(2)O_(5),where x=0,0.5,1 and 1.5 wt.%)have been investigated at room tempera-ture.The dielectric properties of the samples follow the Maxwell-Wagner polarization model.An inverse relationship was found between dielectric constant and AC electrical resistivity for all the samples.The dielectric constants decreased with the addition of V_(2)O_(5),while the electrical resistivities of V_(2)O_(5)-added Ni-Co-Zn ferrites are found to be larger than that of pure Ni-Co-Zn ferrite.The AC conductivity was reduced with the addition of V_(2)O_(5)to Ni-Co-Zn ferrite at lower-frequency region.However,AC conductivity shows a sharp increase at higher-frequency region,which could be attributed to the enhancement of electron hopping between the Fe2+and Fe3+ions in the ferrite matrix due to the activity of the grains.The complex impedance spectroscopy results through Cole-Cole/Nyquist plot have demonstrated a single semicircular arc.It indicates that conduction mechanism takes place predominantly through the grain/bulk property,which could be ascribed to the larger grain size of V_(2)O_(5)-added Ni-Co-Zn ferrites.
