Observation of relaxor ferroelectric behavior in Sn doped BaTiO3 and their energy storage application

Abstract

The presence of particles inside the ferroelectric determines the properties of the material, one of the important functional materials. The unique ferroelectric properties are directly related to the long-range electric dipole arrangement of the ferroelectric domain and its response to external stimuli such as temperature and electric field. However, methods of solid solutions, such as doping, break the long-distance alignment of the dipoles, forming a material known as a relaxor ferroelectric. It shows very different physical properties compared to ferroelectricity. The origin and properties of relaxor ferroelectrics are very interesting from a fundamental point of view with their device applications. Relaxor ferroelectric complex oxide materials have attracted attention due to their dispersion of dielectric constant over a wide range of frequencies and ultrahigh piezoelectric properties has become central in designing electronic applications such as actuators, supercapacitors, and energy storage devices. Thus, the origin of relaxor ferroelectric together with a fundamental understanding enhance the possibility for future applications. Decades of theoretical and experimental studies have extensively explained that the possible existence of nanometer-sized polar clusters, called polar nano-regions (PNRs), are closely associated with fundamental properties. The presence of PNRs in relaxor systems seems to be doubtless; however, due to the lack of the experimental tools that decisively a fundamental question of how the randomly distributed and sized PNRs determine macroscopic characteristics of relaxor systems remains still not addressed. Direct probing of local polarization state of PNRs and their individual dynamics under external perturbation such as electric field will be valuable to address the key issues including the nanoscale polarity fluctuations and switching and the electromechanical response of PNRs. In the thesis, we report on insight into the structural evolution of PNRs and further elaborates on the scientific understanding of the origin of enhanced piezoelectric response in relaxor ferroelectric systems. Furthermore, it will be reported that the presence of these PNRs can be applied to energy storage applications of relaxor ferroelectrics. Despite the significant advancements of dielectric materials, the energy density values of dielectric capacitors are extremely low compared to those of other energy storage systems, e.g., batteries and fuel cells. The deposition of solid solution of ferroelectric and paraelectric multicomponent thin films are the most widely used approach to enhance the energy density of dielectric capacitors; however, it is extremely difficult to determine the optimized composition ratio of two or three components. In this study, we develop ultrahigh energy density single-component Sn-doped BaTiO3 (BTS) epitaxial thin film capacitors. An ultrahigh energy density of 92.5 J/cm3 and energy efficiencies above 78% was successfully achieved in (111)-oriented BTS epitaxial thin film capacitors. These excellent results were attributed to the formation of multi-nanodomains accompanied by delayed polarization saturation, low remnant polarization, high breakdown strength, and high cycling stability. Engineering multi-nanodomains through chemical doping and epitaxial orientation is a facile approach to develop energy-efficient ultrahigh energy density capacitors. This approach can be extended for the design of other single-component-based energy-efficient dielectric capacitors with ultrahigh energy density. We used a method called time resolved X-ray microdiffraction to confirm the structural and electrical changes of PNRs that determine the characteristics of relaxor ferroelectrics, and further confirmed that these characteristics can be applied as energy storage with high performance.