Electromechanical Characterization of Lanthanum Doped Sodium Bismuth Titanate Ceramics

The effect of lanthanum doping is studied on electromechanical properties of lanthanum doped sodium bismuth titanate. The ferroelectric system under investigation is Na_1/2 (La _x Bi _1−x )_1/2 TiO₃ ceramics, with x = 0, 0.1, 0.15 and 0.2. Dielectric and impedance studies have been carried out in the temperature region ranging from room temperature to 550°C and in the frequency range of 100 Hz to 1 MHz. The relaxation behaviour of the charge entities in the above samples is studied as a function of temperature. The structural phase transitions present in the samples showed interesting changes with composition frequency and temperature.

Admittance measurements were carried out in the frequency range of 100 Hz to 13 MHz and in the temperature range of room temperature to 550°C. Combined impedance and admittance spectroscopy was used to analyze admittance data. The electromechanical parameters were calculated from the resonant and anti resonant frequencies obtained from vector admittance plots. The electromechanical coefficients for pure sodium bismuth titanate ceramic samples were found to be much larger than the reported values. And also, it is observed that the lanthanum doping decreased the values of electromechanical coupling coefficients.

Acknowledgments

Paper originally presented at AMF-4, Bangalore, India, December 12–15, 2003