Lead-free perovskite (Bi 0.5 Na 0.5 ) 0.94 Ba 0.06 TiO 3 (BNBT06) was prepared by conventional ceramic fabrication technique at 1160 • C/3h in air atmosphere. The crystal structure, microstructure, dielectric, polarization, piezoelectric properties, and ac conductivity of the sample were studied. X-ray diffraction data confirmed the formation of a single phase tetragonal unit cell. Williamson-Hall plot was used to calculate the lattice strain and the apparent particle size. The experimental relative density of BNBT06 was found to be ∼96-97% of the theoretical one with an average grain size ∼4 μm. Room temperature dielectric constant and loss factor at 1 kHz were found to be equal to 781 and 0.085, respectively. Longitudinal piezoelectric charge coefficient of the poled sample under 2.5 kV/mm at 80 • C in silicone bath was found to be equal to 124 pC/N. Complex impedance and electric modulus spectroscopic analyses showed the dielectric relaxation in the material to be of non-Debye type. The Nyquist plots and conductivity studies showed the NTCR character of BNBT06. The correlated barrier hopping model (CBHM) as well as jump relaxation model (JRM) was found to successfully explain the mechanism of charge transport in BNBT06. The ac conductivity data were used to evaluate the minimum hopping length, apparent activation energy, and density of states at Fermi level.
Lead-free piezoelectric perovskite ceramic (Bi0.5Na0.5)0.95Ba0.05TiO3 (BNT-BT0.05), prepared by conventional high temperature solid state reaction technique at 1160 °C/3h in air atmosphere, is investigated by impedance and modulus spectroscopy in a temperature range 35–400 °C, over a frequency range 100 Hz–1 MHz. The crystal structure, microstructure, and piezoelectric properties as well as the AC conductivity of the sample were studied. Powder X-ray diffraction pattern derived from the resulting data at the room temperature subjected to Rietveld refinements and Williamson-Hall plot analysis confirmed the formation of phase pure compound with monoclinic unit cells having a crystallite-size ~33.8 nm. Observed SEM micrograph showed a uniform distribution of grains inside the sample having an average grain size ~3 mm. Longitudinal piezoelectric charge coefficient of the sample poled under a DC electric field of ~ 2.5 kV/mm at 80 °C in a silicone oil bath was found to be equal to 95 pC/N. The frequency and temperature dependent electrical data analysed in the framework of AC conductivity, complex impedance as well as electric modulus formalisms showed negative temperature coefficient of resistance (NTCR) character of the material and the dielectric relaxation in the material to be of non-Debye type. Double power law for the frequency-dependence of AC conductivity and Jump Relaxation Model (JRM) were found to explain successfully the mechanism of charge transport in BNT-BT0.05
The present work describes the piezoelectric, impedance, and conductivity studies of (Na0.5Bi0.5)1−xBaxTiO3; (1-x)BNT-xBT (0≤x≤1) ceramics. The ceramics were prepared by conventional ceramic fabrication technique. X-ray diffraction data confirmed the formation of a pure compound in all the compositions. Williamson-Hall plot yielded the apparent crystallite sizes ~26–52 nm, and SEM micrograph showed grain sizes ranging between 1.8–3.5 μm for the material samples. Values of longitudinal piezoelectric charge coefficients of the samples poled under a dc electric field of about 2.5 kV/mm at 80°C/15 min indicated that their piezoelectric properties near the MPB are rather sensitive to the phase composition and reach preferred values at x=0.08, where the relative content of the tetragonal phase is significantly higher than that of the monoclinic phase. Complex impedance/modulus spectroscopic analyses indicated the presence of grain-boundary effect along with the bulk contribution and also confirmed the presence of non-Debye type of multiple relaxations in the materials. The temperature dependent electrical conductivity data suggest the negative temperature coefficient of resistance behaviour. The activation energy studies allow insight into the nature of the conduction mechanisms occurring in the materials system which are explained on the basis of hopping model of charge carriers.
The present study addresses the problem of quantitative prediction of effective complex relative permittivity and ac conductivity of (Bi 0.5 Na 0.5 ) 0.94 Ba 0.06 TiO 3 -Polyvenylidene Fluoride (BNBT06-PVDF) 0-3 composite samples (prepared by solution cast method at an elevated temperature) having 10, 20 and 30 volume percentage of BNBT06 powder. SEM micrographs of the fractured surfaces showed that the particle distribution in the grains is not strictly homogeneous. Some areas of agglomeration of particles in the grains are also seen in the micrographs. EDAX patterns confirmed the presence of different constituent elements of the composite samples. The resulting data for room temperature real and imaginary parts of relative permittivity as well as real part of ac conductivity showed an increasing trend with increasing volume fraction of the ceramic filler. The 30 vol. % of BNBT06-PVDF composite had the highest dielectric constant of 75.3 and dielectric loss of ~6.09 i.e., loss tangent ~0.08. Among the dielectric mixing models presented, Rother-Lichtenecker model showed the best fit to the experimental data for the test composite. Similar equations for effective ac conductivity in terms of conductivity of the constituent phases of the composite were proposed in the present work to be fitted to find that none except Rother-Lichtenecker equation fitted the experimental data well. First order exponential growth type of equation applicable to all the three properties fitting the experimental data excellently is also proposed in the present work.
Abstract:The present work describes the use of ac complex impedance and electric modulus spectroscopy techniques to obtain the electrical parameters like electrical conductivity and activation energy of (Bi 0.5
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