Terahertz Dielectric properties of (Ba,Sr)TiO3 systems from First principles

Dielectric permittivity, tunability and loss are dynamical properties of ferroelectrics with many important technological applications. Accurate first-principles based effective Hamiltonian simulations have proven to be an extremely useful tool to investigate these properties of ferroelectrics, since they can: lead to fundamental understanding of GHz/THz range dielectric spectra of materials; aid in optimization of materials for technological applications; resolve controversies’ for example, about exact ferroelectric phase diagram of Pb(Zr,Ti)O₃, or the existence of relaxation mode termed central mode (CM) in epitaxially strained SrTiO₃; predict in advance hitherto undiscovered characteristics; and help discover new more practicable materials for applications.
Room-temperature ferroelectricity in strained SrTiO₃ has been one of the exciting discoveries in recent times and (Ba,Sr)TiO₃ systems in general have been thoroughly spectroscopically investigated for their attractive room temperature dielectric properties. Molecular dynamics (MD) Simulations incorporating first-principles-based effective Hamiltonians for these systems, were conducted to investigate: effects of epitaxial strain and Ba introduction on the complex dielectric response of SrTiO₃ in the GHz/THz regime. Some important revelations from these investigations will be discussed.