Impedance and AC Conductivity Study of (Bi_0.5Na_0.5)TiO₃ –Ba(Zr_0.25Ti_0.75)O₃ Lead-Free Ceramics

Abstract

The polycrystalline (1-x)(Bi_0.5Na_0.5)TiO₃-xBa(Zr_0.25Ti_0.75)O₃ (x = 0.01, 0.03, 0.05 & 0.07) (abbreviated as BNT-BZT) ceramics have been synthesized by conventional solid state sintering technique. X-ray diffraction analysis indicated that a solid solution is formed when Ba(Zr_0.25Ti_0.75)O₃ diffuses into the (Bi_0.5Na_0.5)TiO₃ lattice and a morphotropic phase boundary (MPB) co-existing between rhombohedral and tetragonal region at x = 0.05. The microstructure indicated that the grain size reduces and the shape changes from rectangular to quasispherical with increasing in Ba(Zr_0.25Ti_0.75)O₃ content. Complex Impedance Spectroscopy analysis suggested the presence of temperature-dependent relaxation process in the materials. The modulus mechanism indicated the non-Debye type of conductivity relaxation in the materials, which is supported by impedance data. The ac conductivity was found to obey the universal power law. The activation energies have been calculated from impedance, electric modulus studies and dc conductivity which suggests that the conductions are ionic in nature. The activation energy increases with increasing of BZT content up to x = 0.03 and then decreases which also indicates the presence of morphotropic phase boundary at x = 0.05.

Keywords:

• Morphtropic Phase Boundary (MPB)
• Impedance Spectroscopy
• Electrical Modulus
• Relaxations
• Conductivity

Acknowledgments

Communicated by Dr. Deborah J. Taylor