Effect of Ba2+ in BNT ceramics on dielectric and conductivity properties

Abstract

The polycrystalline (Na0.5Bi0.5)1-xBaxTiO3 (x = 0.026, 0.055 & 0.065) (BNBT) ceramics have been synthesized by conventional solid state sinter-ing technique. The tolerance (t) factor of the BNBT composition have been estimated and found to be 0.988, 0.990 and 0.991 for x = 0.026, 0.055 and 0.065 respectively, revealing system is stable perovskite type structure. The com-pound has a rhombohedral-tetragonal Morphtropic Phase Boun- dary (MPB) at x = 0.065. XRD re-sults indicated the crystalline structure of the investigated materials are of single phase with rhombohedral structure and the average parti-cle size of the calcined powder is found to lie between 45 nm - 60 nm. The effect of Ba2+ on dielectric and conductivity properties in Bis-muth Sodium Titanate (BNT) has been studied. The variation of dielectric constant with fre-quency (45 Hz-5 MHz) and temperature (35℃-590℃) has been performed. The value of Tm and Td are found to decrease with increase of concentration of Barium in BNT. The value of tan in the studied materials is found to be the order of 10-2 indicating low loss materials. The evaluated Curie constant in the composi-tion is found to be the order of 105 revealing the materials belong to oxygen octahedra ferro-electrics. The theoretical dielectric data of the studied composition have been fitted by us- ing Jonscher’s dielectric dispersion relation: . The pre-factor a(T), which indicates the strength of the po-larizability showed a maximum at transition temperature (Tm). The exponent n(T) which gives a large extent of interaction between the charge carriers and polarization is found to be minimum in the vicinity of Tm. The A.C. and d.c conductivity activation energies have been eva- luated; the difference in activation energies could be due to the grain boundary effect. The activation enthalpy energies, have been esti-mated and found to be Hm = 0.37 eV, 0.26 eV and 0.25 eV for BNBT-26, BNBT-55 and BNBT-65 respectively.