BaTiO3 thin films as transitional ferrroelectrics with giant dielectric response

TL;DR

This paper demonstrates that BaTiO3 thin films exhibit giant, temperature-independent dielectric responses due to a unique coexistence of phases enabling polarization rotation, offering a new class of transitional ferroelectrics.

Contribution

It introduces a simple material approach to achieve giant dielectric responses in BaTiO3 thin films through phase coexistence, avoiding complex chemistry and lead-based compounds.

Findings

Giant dielectric response observed in BaTiO3 thin films.

Phase coexistence enables continuous polarization rotation.

Distinct behavior from other ferroelectric materials.

Abstract

Proximity to phase transitions (PTs) is frequently responsible for the largest dielectric susceptibilities in ferroelectrics. The impracticality of using temperature as a control parameter to reach those large responses has motivated the design of solid solutions with phase boundaries between different polar phases at temperatures (typically room temperature) significantly lower than the paraelectric-ferroelectric critical temperature. The flat energy landscapes close to these PTs give rise to polarization rotation under external stimuli, being responsible for the best piezoelectrics so far and a their huge market. But this approach requires complex chemistry to achieve temperature-independent PT boundaries and often involves lead-containing compounds. Here we report that such a bridging state is possible in thin films of chemically simple materials such as BaTiO3. A coexistence of tetragonal, orthorhombic and their bridging low-symmetry phases are shown to be responsible for the continuous vertical polarization rotation, recreating a smear in-transition state and leading to giant temperature-independent dielectric response. These features are distinct from those of single crystals, multi-domain crystals, ceramics or relaxor ferroelectrics, requiring a different description. We believe that other materials can be engineered in a similar way to form a class of ferroelectrics, in which MPB solid solutions are also included, that we propose to coin as transitional ferroelectrics.