Crossover from classical to relaxor ferroelectrics in BaTi1-xHfxO3 ceramics

In this paper we report the successful preparation of hafnium substituted barium titanate, i.e. BaTi1-xHfxO3 (BHT) ceramics with (x = 0.05, 0.1, 0.2, 0.3 and 0.4). X-ray diffraction measurements followed by Reitveld analysis show the single-phase nature of these ceramics undergoing a tetragonal to cubic phase transformation for x >= 0.10. Temperature dependent dielectric properties (epsilon' and epsilon) of these single-phase BHT ceramics have been studied in the temperature range 90-375 K and frequency range 0.1-100 kHz. Dispersionless but hysteric epsilon'-T and epsilon-T behaviour has been observed for x < 0.3 whereas for x >= 0.3 highly diffusive and depressive epsilon'-T and epsilon-T behaviour has been observed. The three different phase transitions of pure BaTiO3 get pinched into a single diffused round peak along with frequency dispersion for x >= 0.3. This clearly indicates an evolution of classical to relaxor ferroelectrics crossover with increasing x in these BHT ceramics. The parameters characterizing the relaxor behaviour have been analysed. The mechanism for the dielectric relaxation process and pinching of phase transition and their effect on ferroelectric behaviour is discussed.