A new-type electro-optic crystal: K3Nb3B2O12

Electro-optical materials are crucial for lasers and modulators applications. Perovskite ferroelectric crystals, characterized by oxygen octahedrons and superior dipole migration capabilities, are recognized for their high electro-optic coefficients. However, the application of perovskite ferroelectric crystals is often limited by reduced optical transparency, which results from light scattering and reflection at domain walls. In this study, we implemented a structure dimensionality reduction strategy to successfully transform a three-dimensional structure KNbO₃ (KNO) crystal into a quasi-two-dimensional layered structure K₃Nb₃B₂O₁₂ (KNBO) crystal through BO₃ planar groups. This modification restricts the mobility of B-site ions within the layers while preserving significant spontaneous polarization along the interlayer direction, thus converting multipolar axis into a unipolar axis in the ferroelectric. This alteration in the direction of spontaneous polarization modifies the domain structure, thereby minimizing the scattering effects of the domain walls. As a result, the KNBO crystal exhibits a large effective electro-optic (EO) coefficient of 50.14 pm/V and a high transmittance exceeding 80% in the 330 nm to 2500 nm wavelength range. These properties surpass those of currently available commercial EO crystals. This research establishes a model for enhancing transparency and EO coefficient through structural design, offering potential applications to other EO crystals.