Crossover from classical to relaxor ferroelectrics in BaTi_1−xHf_xO₃ ceramics

In this paper we report the successful preparation of hafnium substituted barium titanate, i.e. BaTi_1−xHf_xO₃ (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 (ε^' and ε^'') 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 ε^'–T and ε^''–T behaviour has been observed for x<0.3 whereas for x≥0.3 highly diffusive and depressive ε^'–T and ε^''–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.