Syed Mahboob

Impedance and a.c. conductivity studies on Ba(Nd0.2Ti0.6Nb0.2)O3 ceramic prepared through conventional and microwave sintering route

Electrical conduction studies on Ba(Nd0.2Ti0.6Nb0.2)O3 ceramic samples prepared through conventional and microwave sintering route are presented in this paper. D.C. and a.c. conductivities of these samples as a function of temperature from 300–900 K have been studied. Two types of conduction processes are evident from the frequency dependant conductivity plots, i.e. low-frequency conduction due to short-range hopping and high-frequency conduction due to the localized relaxation (reorientational) hopping mechanism. Grain and grain boundary contributions to the conductivity in these samples are obtained from impedance/admittance measurements via equivalent circuit modelling.

Electrical conduction in (Na0.125Bi0.125 Ba0.65Ca0.1)(Nd0.065Ti0.87Nb0.065)O3 ceramic)O3 ceramic

Polycrystalline ceramic samples of sodium bismuth titanate with simultaneous doping at A and B sites have been studied for the influence of these dopants on the electrical conduction mechanism. A.C. conductivity measurements were done on the prepared sample in a wide range of frequency and temperature. These studies revealed that the conduction in the sample arises due to hopping of bound charges. Four-term power law is used to characterize the frequency dependence of a.c. conductivity. From the temperature dependence of the exponents, the a.c. conduction in the samples is explained.

Dielectric Properties of BaTiO3 Based Lead Free Relaxor Prepared Through Conventional and Microwave Sintering

Dielectric ceramics with compositions belonging to the Ba(Nd x Ti1−2x Nb x )O 3 with varying concentration of x were prepared through Solid State Sintering route using both conventional and microwave sintering. The phase transformations were studied by dielectric measurements in a wide range of temperature and frequency. The relaxor behaviour is almost favoured as the composition deviates more from BaTiO 3 and as the substitution is heterovalent in the 6-coordination number crystallographic site.

Dielectric and Piezoelectric Properties of Microwave Sintered Ba1-xRexTiO3 Ceramics

Lead free piezoelectric ceramic Ba1-xRexTiO3 (Re = Ce and Pr with x = 0.003) were prepared through microwave sintering route using 5% SiO2 as sintering aid. The dielectric, impedance and piezoelectric properties were studied over a wide range of temperature. Pr doped barium titanate showed higher value of dielectric constant around 15,099. The electromechanical coupling factors at 225°C are 0.9985 and 0.9978 for Ce and Pr doped barium titanate ceramics respectively. The d33 values for Ce and Pr doped barium titanate ceramics at 225°C are 368 nm.V−1 and 470 nm.V−1 respectively. The d33 value decreased with the increase of temperature and the values at 600°C are 10 nm.V−1 and 8 nm.V−1 for Ce and Pr doped barium titanate ceramics respectively.

DEGREE OF DIFFUSED PHASE TRANSITION AND NON-DEBYE DIELECTRIC RELAXATION IN Ba(NdxTi1-2xNbx)O3 CERAMICS

Dielectric measurements were made over the temperature range 80–300 K at different frequencies (10 kHz, 50 kHz, 100 kHz, 500 kHz and 1 MHz). The degree of relaxor behavior and diffuseness of phase transition were correlated to the cationic disorder at lattice site B. Non-Debye dielectric behavior was observed in the present samples and a modified Arrhenius relation proposed by Chen et al. was found to best describe the frequency dependent dielectric maxima temperature.

Modified Lorentz and Gauss Equations to Describe the Dielectric Behaviour of Sr1-2xNaxNdxBi4Ti4O15 Normal Ferroelectric Compounds

Modified Lorentz and Gauss equation is proposed to describe the temperature dependence of dielectric constant for bismuth layered structure ferroelectric materials i.e. Sr1-2xNaxNdxBi4Ti4O15. The validity of the proposed equation was checked from the regression value obtained. The activation energy for orientation of dipoles, static dielectric constant and infinite dielectric constant obtained from the non linear curve fitting to experimental data by using modified Lorentz and Gauss equation have reasonable values. Modified Lorentz equation is found to be the best fit to the experimental dielectric data. The above modified equations may also be used to describe the dielectric behaviour of other normal ferroelectric materials which show sharp transitions.

Characterization of Piezoelectric Ceramic [Ba(Nd0.1Ti0.8Nb0.1)O3]0.40[Na0.5Bi0.5TiO3]0.40[CaTiO3]0.20

[BaNd0.1Ti0.8Nb0.1O3]0.40[Na0.5Bi0.5TiO3]0.40[CaTiO3]0.20 ceramic was prepared through solid state sintering method. The phase and microstructure of ceramic sample were characterized by X-ray diffraction (XRD) and Scanning electron microscopy (SEM). The XRD results indicate that the ceramic sample have a cubic structure at room temperature. The average grain size was found to be 2 4 μm. The dielectric and piezoelectric properties were also investigated. From capacitance measurements, the values of Kt, Keff and d33 at room temperature were 0.816, 0.788 and 15.4 pm.V−1 respectively. From modulus data, the Kt and Keff at 325°C are 0.9995 and 0.9994 respectively. The piezoelectric constant (d33) decreased with the increase of temperature and the value of d33 at 325 °C was found to be 8.58 nm.V−1.

Dielectric Relaxor Ceramics – Solid Solution of Na0.5Bi0.5TiO3 with Ba(Nd0.1Ti0.8Nb0.1)O3

Ceramic compositions [Ba(Nd0.1Ti0.8Nb0.1)O3](1-x) [Na0.5Bi0.5TiO3]x with x = 0.0, 0.25, 0.40, 0.50, 0.55, 0.60, 0.65 and 0.70 were prepared by modifying the relaxor dielectric material Ba(Nd0.1Ti0.8Nb0.1)O3 with ferroelectric Na0.5Bi0.5TiO3 using conventional solid state sintering route. The X-ray diffraction studies revealed that the ceramic compositions with x = 0.0, 0.25 and 0.40 are of cubic structure at room temperature and the ceramic compositions with x = 0.60, 0.65 and 0.70 are of rhombohedral structure at room temperature. However, ceramic compositions with x = 0.50, 0.55 show extra peaks indicating that the compositions do not form in to single phase. Dielectric studies revealed that all the ceramic compositions exhibited typical relaxor behaviour and the dielectric maximum temperature is found to increase with the increase of x value. The transition temperatures, degree of relaxor behaviour and diffuseness of phase transitions are related to the steric effect and random distribution of cations at lattice sites respectively. Polarization studies are also done on the samples and results are discussed.

Dielectric, impedance and electromechanical studies on [Ba(Nd0.1Ti0.8Nb0.1)O3]1-y[Na0.5Bi0.5TiO3]y relaxor ceramics prepared through conventional and microwave sintering route

ABSTRACT [Ba(Nd0.1Ti0.8Nb0.1)O3](1-y)[Na0.5Bi0.5TiO3]y ceramics were prepared through solid state sintering (CS) and microwave sintering (MWS) route. The XRD results indicate that the ceramic samples have a cubic structure at room temperature. The dielectric, electromechanical and piezoelectric properties were also investigated. Relaxor behaviour was observed for the present ceramic samples prepared through both the sintering routes. The degree of diffusiveness of phase transition and relaxor behaviour are more for CS ceramic when compared to MWS ceramic with y = 0.40. From modulus measurements, the values of Kt, Keff and d33 at 623 K were 0.99983, 0.99980 and 5.273 nm.V−1 respectively for MWS ceramic with y = 0.25. The piezoelectric constant (d33) decreased with the increase of temperature. The d33 values are higher for the microwave sintered ceramic samples when compared to conventional sintered ceramic samples.

Modified Lorentz equation to describe the resonance and anti-resonance behaviour of piezoelectric ceramics

ABSTRACT Modified Lorentz equation is proposed to describe the resonance and anti-resonance behaviour of piezoelectric ceramics. It is applied to Ba(NdxTi1−2xNbx)O3, (Na0.5Bi0.5)(NdyTi1−2yNby)O3 and Sr1−2zNazNdzBi4Ti4O15 piezoelectric ceramics by non linear curve fitting to experimental data to check its validity. The validity is checked from the regression values obtained. The static dielectric constant, infinite dielectric constant, polarizability, piezoelectric charge constant and piezoelectric voltage constant obtained from the non linear curve fitting to experimental data by using modified Lorentz equation have reasonable values. The above modified equation may also be used to describe the resonance and anti-resonance behaviour of other piezoelectric ceramics.