Electrical anisotropy in the hot-forged CaBi_4Ti_4O_(15) ceramics

摘要

Textured CaBi_4Ti_4O_(15) (CBT) ceramics have been fabricated via a hot-forging technique. The effect of grain orientation on the dielectric and electrical properties is studied by impedance (Z*) and modulus (M*) spectroscopy. The degree of orientation (F) calculated from X-ray diffraction pattern is found to be 89.4 percent along the c-axis of the crystal structure. The permittivity was measured along both perpendicular and parallel directions of the forging axis. The ratio of permittivity along perpendicular to parallel direction is found to be approx 3 at the Curie temperature of 797 deg C. The non-superimposition of the normalized Z" and M" vs. frequency plot revealed the conduction in the material is localized and deviate from ideal Debye behavior. The power law exponent n of the material has been explained on the basis of jump relaxation model and revealed the conduction through grain boundary. Activation energy (E_a) is obtained from Arrhenius plots of the dc conductivity for both the ceramics and it is found to be 0.89 eV and 0.78 eV for CBT (||) and CBT (perpendicular), respectively.