Crystal structures, ferroelectric properties, and piezoelectric properties of Sn-doped epitaxial BaTiO₃ thin films

We investigated the crystal structures, ferroelectric properties, and piezoelectric properties of Sn-doped BaTiO₃ (SBTO) thin films on Pt/MgO substrates. Epitaxially c-oriented SBTO thin films with Sn doping concentrations of 0, 5, 10, and 15% were. The SBTO thin films with Sn doping concentrations of 10 and 15% showed a mixed state of a-domains and c-domains, where the a-domain concentration increased with the Sn doping concentration. In the ferroelectric hysteresis loop of the SBTO thin films, the remanent polarization and saturation polarization of the SBTO thin film with the Sn concentration increased to 5% increased significantly. On the other hand, the SBTO thin films with increased Sn concentrations of 10% and 15% have remanent polarizations reduced by the formation of a-domains. In particular, in the piezoelectric hysteresis loops of the SBTO thin films, the piezoelectric coefficients increased as the concentration of a-domains increased because the mixture of a-domains and c-domains indicates the formation of 90° domains. The SBTO thin film with a Sn concentration of 15% exhibited the highest piezoelectric coefficient due to the high a-domain concentration.