Engineering Electro-Optic BaTiO 3 Nanocrystals via Efficient Doping.

Electro-optic (EO) modulators provide electrical-to-optical signal conversion relevant to optical communications. Barium titanate (BaTiO ) is a promising material system for EO modulation in light of its optical ultrafast nonlinearity, low optical loss, and high refractive index. To enhance further its spontaneous polarization, BaTiO can be doped at the Ba and Ti sites; however, doping is often accompanied by ion migration, which diminishes EO performance. Here, donor-acceptor doping and its effect on EO efficiency are investigated, finding that La-doped BaTiO achieves an EO coefficient of 42 pm V at 1 kHz, fully twice that of the pristine specimen; however, it is also observed that, with this single-element doping, the EO response falls off rapidly with frequency. From impedance spectroscopy, it is found that frequency-dependent EO is correlated with ion migration. Density functional theory calculations predict that the ion-migration barrier decreases with La doping but can be recovered with further Mn doping, a finding that prompts to prevent ion migration by incorporating Mn into the Ti-site to compensate for the charge imbalance.