Permittivity boosting by induced strain from local doping in titanates from first principles

Area of Science:

• Materials Science
• Solid State Physics
• Computational Materials Science

Background:

• Parતelectric titanates exhibit interesting dielectric properties.
• Understanding factors influencing ionic dielectric constant is crucial for advanced materials.
• Previous studies have explored doping effects on dielectric properties.

Purpose of the Study:

• To investigate the impact of isovalent substitutions and co-doping on the ionic dielectric constant of various titanate structures.
• To identify mechanisms responsible for enhanced dielectric permittivity.
• To propose new materials with potential for colossal permittivity.

Main Methods:

• Density Functional Perturbation Theory (DFPT) was employed.
• Analysis of perovskite, Ruddlesden-Popper, and rutile titanate phases.
• Investigation of structure-property relationships, including local strain and bond lengths.

Main Results:

• Isovalent substitutions and co-doping increase the ionic dielectric constant (εion) of titanates.
• Dynamically stable structures with εion ranging from 10^2 to 10^4 were identified.
• Local defect-induced strain and maximum Ti-O bond length were found to be key factors.
• The Ti-O phonon mode, crucial for high dielectric constants, is tunable via strain and symmetry lowering.

Conclusions:

• The study attributes the colossal permittivity in co-doped rutile to the lattice polarization mechanism.
• Maximum Ti-O bond length serves as a descriptor for enhanced ionic permittivity.
• New perovskite- and rutile-based systems with potential for colossal permittivity were identified.