Domain Engineering Enabled Giant Linear Electro-Optic Effect and High Transparency in Ferroelectric KTa_1−xNb_xO₃ Single Crystals

A giant linear electro-optic (EO) effect and high transparency in ferroelectric potassium tantalate niobate [((Formula presented.)), KTN] crystal is achieved via a thermally controlled domain engineering method. It involves a two-step thermal annealing process: 1) a rapid cooling process that forms polar nano-regions (PNRs), i.e., a cooling rate of (Formula presented.) from (Formula presented.) to (Formula presented.) where (Formula presented.) is the Curie temperature; and 2) a slow cooling process that facilitates abnormal domain growth (AGG) i.e., a cooling rate of (Formula presented.) from (Formula presented.) to (Formula presented.). Since PNR can have a faceted boundary and high anisotropy, it can promote AGG within single crystals to realize solid-state domain conversion macroscopically from a multi-domain to single-domain crystal within a slow cooling process. The resultant KTN crystal offers high transparency that is equivalent to its paraelectric phase; and a linear EO coefficient ((Formula presented.)) as large as (Formula presented.), which is five times the value of conventional KTN crystals with similar composition. This giant linear EO coefficient represents a major technical advance in EO materials and significantly reduces the driving voltage, power, and footprint of many types of EO devices.