DIELECTRIC MEASUREMENTS AND IMPEDANCE SPECTROSCOPY OF Ba-MODIFIED (Na 0.5Bi0.5)TiO₃ PREPARED BY THE HYDROTHERMAL METHOD

Abstract

1-x)(Na 0.5 Bi 0.5 )TiO 3-x BaTiO 3 , Rietveld refinement, Hydrothermal method, Nyquist impedance plot, Diffuse ferroelectric behaviour Sodium bismuth titanate (Na 0.5 Bi 0.5 )TiO 3 perovskite is presented as a lead-free concurrent for electro-ceramic engineering technologies. In this paper, (1-x)(Na 0.5 Bi 0.5 )TiO 3-x BaTiO 3 type ceramic materials were obtained by the hydrothermal process at a very low heat treatment temperature of around 200 °C and for times up to 24 hours. The structural, microstructural, and dielectric properties of the ceramic materials were investigated. The X-ray diffraction analysis confirms the formation of the rhombohedral phase of NBT with space group R3c. Based on the Rietveld refinement, the morphotropic phase boundary (MPB) was determined for the composition x (%) = 5 and 7. The grains increase in size from 11 to 23 µm and their distribution widens with an increasing barium concentration in the morphotropic phase boundary. The dielectric constants were measured from room temperature to 600 °C for various frequencies in the range of 1 kHz -2 MHz. From the Nyquist impedance plot, the effect of the grain and the grain boundaries on the electrical properties was studied. At high temperatures, the Uchino law modified by Echatoui et al. allows one to describe the thermal variation of the permittivity. This diffuse character is attributed to a cationic disorder due to the distribution of Na + /Bi 3+ and Ba 2+ ions in the A site.