Microstructure and bidirectional dielectric tunability behaviour of Nd³⁺-doped KSr₂Nb₅O₁₅ lead-free ceramics

The luminescence modulation behaviour under the in-situ electric field of rare-earth doped KSr₂Nb₅O₁₅ ceramics opened a new door for the development of dielectric materials. Where the understanding the effect of rare-earth doping on the electric properties of host, especially at the similar doping concentration with luminescence researches (low concentrations) is very important for the exploration of mechanism of electric-luminescent coupling effect. In this work, Nd³⁺-doped KSr₂Nb₅O₁₅ (KSN-xNd) ceramics were synthesized, and the electric properties were investigated systematically. Our results suggest that the Nd³⁺ doping slightly increased the phase transition temperatures and improved the piezoelectric response of KSr₂Nb₅O₁₅. Most importantly, a bidirectional dielectric tunability is revealed in KSr₂Nb₅O₁₅. The dielectric permittivity can be adjusted by the DC electric bias, with tunability ranging from −12.3% to 21.9%. The related mechanism and relationship between the bidirectional dielectric tunability and ferroelectricity are revealed by temperature-dependent dielectric and ferroelectric characterization. The researches of electric properties and bidirectional dielectric tunability of KSN-based ceramics paved the way to further exploration of electric-luminescent coupling mechanism.