Defect engineering by annealing: Managing the trade-off relationship between photochromic and electrical properties in KNN-based translucent ceramics

Rare-earth-doped transparent ferroelectrics exhibit outstanding optical transparency, photoluminescence (PL), photochromic (PC) and various electrical properties, showing potential for use in optoelectronic applications. However, there is an inevitable trade-off relationship between optical and electrical coupling during the integration of multifunctionality. In this work, Ba ²⁺, Ho ³⁺ and Yb ³⁺ were codoped in KNN translucent-ferroelectric ceramics (as a model material) to overcome the contradiction between optical (transparency/PC) and electrical properties (resistivity/ferroelectricity). The defects (mainly oxygen vacancies) within the ceramics can be effectively regulated through annealing under different atmospheres. At the cost of a slight decrease in PC performance, the electrical properties significantly improved; i.e., for the optimal ceramic annealed in an oxygen atmosphere, both the maximum and remnant polarizations nearly doubled, and the resistivity significantly decreased compared to that of the original sample. A mechanism for regulating these properties was proposed. This research serves as a valuable example for adjusting the optical and electrical properties of other ferroelectrics through annealing.