Role of ferroelectric polarization during growth of highly strained ferroelectrics revealed by in-situ x-ray diffraction

TL;DR

This study reveals that ferroelectric polarization influences the growth dynamics and properties of thin films, suggesting polarization engineering as a new approach alongside strain engineering.

Contribution

It demonstrates how ferroelectric polarization affects growth mechanisms and properties in multilayer thin films, introducing polarization engineering as a novel growth control method.

Findings

Polarization impacts growth rates and relaxation mechanisms.

In-situ x-ray diffraction reveals polarization effects during growth.

Energy considerations explain polarization-driven growth changes.

Abstract

Strain engineering of perovskite oxide thin films has proven to be an extremely powerful method for enhancing and inducing ferroelectric behavior. In ferroelectric thin films and superlattices, the polarization is intricately linked to crystal structure, but we show here that it can also play an important role in the growth process, influencing growth rates, relaxation mechanisms, electrical properties and domain structures. We have studied this effect in detail by focusing on the properties of BaTiO$_{3}$ thin films grown on very thin layers of PbTiO$_{3}$ using a combination of x-ray diffraction, piezoforce microscopy, electrical characterization and rapid in-situ x-ray diffraction reciprocal space maps during the growth using synchrotron radiation. Using a simple model we show that the changes in growth are driven by the energy cost for the top material to sustain the polarization imposed upon it by the underlying layer, and these effects may be expected to occur in other multilayer systems where polarization is present during growth. Our research motivates the concept of polarization engineering during the growth process as a new and complementary approach to strain engineering.