Synthesis and characterizations of novel antiferroelectric and relaxor materials for energy storage applications

For technological applications such as portable electronics and automobiles, materials that exhibit high power density and high energy density at a low applied electric field are needed. Conventional dielectric capacitors have been widely used for pulse power applications due to their high charge/discharge speed, high power density, wide temperature range applicability and insensitivity to magnetic fields, but unfortunately, their energy density is low, especially at low electric fields. To address these issues, in this thesis work, novel oxide perovskite solid solutions of antiferroelectric properties and relaxor behaviour have been designed, synthesized, characterized, and explored in terms of crystal structures, dielectric, ferroelectric, antiferroelectric and relaxor properties, and energy storage performance. The prototypical antiferroelectric (AFE) lead hafnate PbHfO3 is first investigated for its room temperature and high temperature energy storage performance. The recoverable energy density (Wrec) at room temperature is found to be 286 % higher than the values reported so far, and the AFE characteristics of the intermediate (IM) phase are revealed for the first time. Next, the solid solution after AFE PbZrO3 and ferroelectric BiAlO3 is synthesized and characterized. It is found that the substitution of BiAlO3 results in an IM phase that is different from the IM in PbZrO3. Then, the solid solution of (1-x) PbHfO3-xBiAlO3 is designed and synthesized to soften the AFE order in PbHfO3, resulting in a Wrec = 0.24 J/cm3 at room temperature (130 kV/cm). To investigate the nature of dielectric relaxation and freezing behaviour in weakly ferroelectric AgNbO3, the solid solution of (1-x)AgNbO3-xPbZrO3 is prepared to tune the M-phases at/below room temperature. An improper reentrant relaxor behaviour is discovered at the M1↔M2 phase transition for the first time. Moreover, a new solid solution of (1-x)PbHfO3-xAgNbO3 is designed based on the concept of dipole frustration, and synthesized in the form of ceramics. It produces high maximum polarization (55 μC/cm2 for x = 0.027) at low electric field due to significantly enhanced A-site cation displacement, resulting in Wrec = 4.8 J/cm3, which is the highest energy storage density at a relatively low applied field of 173 kV/cm compared with other AFEs. Lastly, a novel relaxor-ferroelectric solid solution of (1-x)BaZr0.3Ti0.7O3-xBiAlO3 is prepared and investigated. The substitution of BiAlO3 is found to enhance the dielectric relaxation, leading to a Wrec that is 96 % higher than that of pure BaZr0.3Ti0.7O3.