Investigation of crystal structure and variable range hopping conduction mechanism in Gd doped Na0.5Bi0.5TiO3 ceramics

Abstract

We report the crystal structure, dielectric, and conductivity properties of Gd doped Na0.5Bi0.5TiO3 i.e., [Bi(1-x)Gdx]0.5Na0.5TiO3 (x: 0.00, 0.01, 0.02, 0.03 and 0.04) ceramics prepared by solid-state reaction method. Rietveld refinement results of X-ray diffraction data suggest that all the sample exhibit rhombohedral crystal structures with the R3c space group. We have adopted the Megaw and Darlington formalism of atomic positions for the R3c space group to refine the crystal structure. The primary XRD reflection around 32° i.e., (104)/ (110) initially shifts to a higher angle up to x ≤ 0.02 and then moves towards a lower angle for a higher doping level, indicating the presence of an amphoteric nature. The deconvolution of the Raman peak was carried out using the Lorentz function and a broadening in the Raman modes with a raise in Gd percentage was observed. The temperature-dependent dielectric data show that the temperature corresponding to maximum dielectric permittivity (Tm) increases with Gd content whereas the Td declines with increasing composition. The variation of conductivity as a function of the temperature of the samples was examined by Arrhenius's equation and Mott's variable-range hopping mechanism. Above x = 0.02, activation energy values at high temperature increase in Gd content, which suggest ferroelectric hardening that resulted due to acceptor type Gd3+ doping. The parameters like hopping length (RH), the density of states (N(EF)), and hopping energies (WH) were calculated from the fitting of the model. The above results are expected to provide the fundamental importance of ferroelectric hardening and p-type conductivity in Na0.5Bi0.5TiO3-based perovskites.