Phase transitions in ferroelectrics are of large technological importance for modern electronic devices as they allow for exceptional functional properties such as giant dielectric, piezoelectric, and electrocaloric responses. Designing materials with optimal responses requires the control of phase stabilities, transition temperatures, critical field strengths to induce a transition, and the thermal hysteresis of the transition. Material systems with compositional complexities have commonly been used to tune the phase stabilities and transition temperatures, however, less is known on the impact of the microstructure. Even with advances in experimental tools, it is still challenging [1]. In this theoretical work, we use \textit{ab initio} based molecular dynamics simulations to explore how the microstructures (defects, inhomogeneities, domain walls) and non-collinear electric fields may be used to optimize the phase stabilities and the properties of the ferroelectric-to-ferroelectric phase transition in (Ba,Sr)TiO$_3$ solid solutions.

[1] A. Grünebohm, M. Marathe, R. Khachaturyan, R. Schiedung, D. Lupascu, and V. Shvartsman. Interplay of domain structure and phase transitions: Theory, experiment and functionality. J. Phys.: Condens. Matter, 2021.