Related Articles Conductivity and frequency dependent specific absorption rate (original) (raw)
Related papers
2000
Particulate composites of ferrite and ferroelectric phases with xNiFe 2 O 4 (NF) and (1 À x)Pb 0.988 (Zr 0.52 Ti 0.48) 0.976 Nb 0.024 O 3 (where x ¼ 2, 10, 20, 30, 50, 70, and 100 wt. %) were prepared in situ by sol-gel method. The presence of a diphase composition was confirmed by X-ray diffraction while the microstructure of the composites was studied by scanning electron microscopy revealing a good mixing of the two phases and a good densification of the bulk ceramics. The dielectric permittivity shows usual dielectric dispersion behavior with increasing frequency due to Maxwell-Wagner interfacial polarization. AC conductivity measurements made in frequency range 1 Hz-1 MHz suggest that the conduction process is due to mixed polaron hopping. The effect of NF phase concentration on the P-E and M-H hysteresis behavior and dielectric properties of the composites was investigated. At low NF concentration a sharp ferro-paraelectric transition peak can be observed at around 360 C while for higher NF concentrations a trend to a diffuse phase transition occurs. All the composite samples exhibit typical ferromagnetic hysteresis loops, indicating the presence of ordered magnetic structure. V
Ferroelectric and dielectric properties of ferrite-ferroelectric ceramic composites
Journal of Applied Physics, 2013
Particulate composites of ferrite and ferroelectric phases with xNiFe 2 O 4 (NF) and (1 À x)Pb 0.988 (Zr 0.52 Ti 0.48 ) 0.976 Nb 0.024 O 3 (where x ¼ 2, 10, 20, 30, 50, 70, and 100 wt. %) were prepared in situ by sol-gel method. The presence of a diphase composition was confirmed by X-ray diffraction while the microstructure of the composites was studied by scanning electron microscopy revealing a good mixing of the two phases and a good densification of the bulk ceramics. The dielectric permittivity shows usual dielectric dispersion behavior with increasing frequency due to Maxwell-Wagner interfacial polarization. AC conductivity measurements made in frequency range 1 Hz-1 MHz suggest that the conduction process is due to mixed polaron hopping. The effect of NF phase concentration on the P-E and M-H hysteresis behavior and dielectric properties of the composites was investigated. At low NF concentration a sharp ferro-paraelectric transition peak can be observed at around 360 C while for higher NF concentrations a trend to a diffuse phase transition occurs. All the composite samples exhibit typical ferromagnetic hysteresis loops, indicating the presence of ordered magnetic structure. V C 2013 American Institute of Physics.
Bull. Mater. Sci., Vol. 30, No. 4, August 2007, pp. 357–363.
Ferroelectromagnetic composites with compositions, X Ni 0⋅5 Zn 0⋅5 Fe 1⋅95 O 4-δ + (1 -X) Ba 0⋅8 Pb 0⋅2 TiO 3 , in which X varies as 0, 0⋅005, 0⋅010, 0⋅015, 0⋅020, 0⋅040, 0⋅060, 0⋅080 and 1 in mole %, were prepared by conventional ceramic double sintering process. The presence of two phases was confirmed by X-ray diffraction. The temperature variation of dielectric constant, ε , dielectric loss, tan δ, d.c. conductivity, a.c. conductivity, elastic and anelastic behaviour of ferrite-ferroelectric composites were studied in the temperature range 30-350°C. The a.c. conductivity measurements on these composites in the frequency range 100 Hz-1 MHz at room temperature reveal that the conduction mechanism is due to small polaron hopping. The dielectric and elastic data were discussed in the light of phase transitions.
Multiferroic composites with equal weight fractions of bismuth ferrite/manganese doped bismuth ferrite and nickel-zinc ferrite with the chemical formulae, 0.5(BiFeO 3 )-0.5(Ni 0.5 Zn 0.5 Fe 2 O 4 ) and 0.5(Bi 0.95 Mn 0.05 FeO 3 )-0.5(Ni 0.5 Zn 0.5 Fe 2 O 4 ) have been prepared using sol-gel autocombustion and solid state methods and investigated to understand the effects of manganese on various structural, dielectric and impedance properties. X-ray diffraction analysis of the composites reveals the formation of di-phase compounds while retaining the spinel and rhombohedrally distorted perovskite phases for the nickel-zinc ferrite and bismuth ferrite/manganese doped bismuth ferrites, respectively. Scanning electron microscopy measurements on the sintered surfaces of the samples display uniformly well knitted fine grained microstructures with thin grain boundaries. Dielectric properties of the composites have been studied in a wide range of frequencies from 1 Hz to 1 MHz and at different temperatures in the range from 30 to 350 1C. Observed temperature dependent diffuse dielectric anomalies, one at around 180-270 1C and the other at around 270-340 1C, were attributed to structural inhomogeneities and dipole induced charge carrier hopping motions at low temperature, and to magnetic phase transitions at high temperatures. Impedance analysis on the samples help to understand the contributions of electrical conductivity and interfacial polarization, and the observed results are in support of the arguments made during the analysis of dielectric properties. The results of all these measurements clearly emphasize the presence of Mn to bring about significant changes in the microstructure, conductivity and impedance properties leading to reduced dielectric losses.
Advances in Condensed Matter Physics, 2010
Novel ferromagnetic-dielectric particulate composites of Ni0.5Zn0.5Fe1.95O4−δ(NZF) and PbZr0.52Ti0.48O3(PZT) were prepared by conventional ceramic method. The presence of two phases in composites was confirmed by XRD technique. The variations of dielectric constant () with frequency in the range of 100 kHz–1 MHz at room temperature and also with temperature at three different frequencies (50 kHz, 100 kHz, and 500 kHz) were studied. Detailed studies on the dielectric properties were done confirming that the magnetoelectric interaction between the constituent phases may result in various anomalies in the dielectric behaviour of the composites. It is proposed that interfaces play an important role in the dielectric properties, causing space charge effects and Maxwell-Wagner relaxation, particularly at low frequencies and high temperatures. The piezoelectricd33constant was studied at room temperature, and thed33constant value decreased with ferrite content. Magnetic properties likeB-Hlo...
Ceramics International, 2013
Composites having general formula 0.1Ni 0.8 Zn 0.2 Fe 2 O 4-0.9Pb 1−3x/2 Sm x Zr 0.65 Ti 0.35 O 3 with x ¼0, 0.01, 0.02 and 0.03 were synthesized by a conventional solid state reaction route. X-ray diffraction analysis was carried out to confirm the coexistence of individual phases and microstructural study was done by using a scanning electron microscope. Dielectric properties were studied as a function of temperature and frequency. To study ferroelectric and magnetic ordering in composite samples, P-E and M-H hysteresis loops were recorded respectively. Maximum magnetoelectric coupling coefficient of 22.5 mV/cm Oe was observed for sample with x ¼0.03. A significant improvement in dielectric, ferroelectric, piezoelectric and magnetoelectric properties was observed for Sm substitution.
The presence of superlattice reflections and detailed analyses of the powder neutron and x-ray diffraction data reveals that La rich (BF 0.50 -LF 0.50 ) 0.50 -(PT) 0.50 (BF-LF-PT) has ferroelectric rhombohedral crystal structure with space group R3c at ambient condition. The temperature dependence of lattice parameters, tilt angle, calculated polarization (P s ), volume, and integrated intensity of superlattice and magnetic reflection show an anomaly around 170 K. Extrapolation of P s vs. T curve indicates that the ferroelectric transition temperature in this La rich BF-LF-PT solid solution is at T c FE = 523 K. Impedance spectroscopy, dielectric spectroscopy and ac conductivity measurements were performed in temperature range 473K≤T≤573K to probe the origin of large remnant polarization and frequency dependent broad transitions with large dielectric constant near T c FE . Results of impedance spectroscopy measurements clearly show contributions of both grain and grain boundaries throughout the frequency range (10 2 Hz ≤ f ≤ 10 7 Hz).
Electrical behavior of Pb(Zr0.52Ti0.48)0.5(Fe0.5Nb0.5)0.5O3 ceramics
Materials Chemistry and Physics, 2011
Polycrystalline sample of Pb(Zr 0.52 Ti 0.48 ) 0.5 (Fe 0.5 Nb 0.5 ) 0.5 O 3 (PZTFN) ceramics was prepared by a hightemperature solid-state reaction technique. Preliminary X-ray diffraction analysis confirms the formation of single phase compound with tetragonal crystal structure. The dielectric behavior of the material was studied in a wide frequency (100 Hz-1 MHz) and temperature (30-500 • C) range. The relationship between dielectric constant ε r and temperature showed a single Curie transition temperature (T c = 255 • C), with as large a ε r value as 4200 at T c . A low value of dissipation factor (tan ı), as small as 0.04 up to temperature above than T c (frequency f = 1 kHz), with good insulating properties made the sample for prospective applications in microwave dielectric components and high-power-density capacitors. The higher diffusivity (␥ ∼ 1.6) value of the dielectric peak in the material indicates the greater disordering in the system. The signature of ac conductivity depending upon frequency and temperature exhibits the presence of different type of charge species. It is observed that oxygen vacancy plays an important role for high temperature conduction mechanism and dynamics of polarization of the system.