DescriptionThis thesis contains several research works on ferroelectric and ferro-rotational domains in complex oxides. The first chapter starts with a review on the history of ferroelectricity and a brief introduction on the concept of proper and improper ferroelectricity. The relatively new concept of hybrid improper ferroelectricity is extensively discussed with the showcase of several associated oxide systems. In the second chapter, we demonstrate that the flux-method-grown CsBiNb₂O₇ single crystals exhibit the largest spontaneous polarization ever found in the like of hybrid improper ferroelectrics. Ferroelastic domain wall motion under high voltage poling is also observed. In the third chapter, we systematically investigate the domain topology of floating-zone-grown BiFeO₃ single crystals and the conductivity of 109° and 71° domain walls. Chapter 4 and 5 focus on a recently defined new ferroic order, ferro-rotational order, and a specific ilmenite system. An innovative domain imaging method utilizing a special sample polishing technique was introduced in Chapter 4. The selective coupling between the microscopic ferro-rotational order and a macroscopic circular rotation is reported for the first time. Another two methods exploiting the same mechanism were also utilized to reveal the ferro-rotational domain patterns. Chapter 5 follows the content of chapter 4 and quantitatively investigates the relationship between the domain density and the sample cooling rate across the transition temperature. The result agrees well with the prediction of Kibble-Zurek mechanism in the three-dimensional Ising universality class.