Entropy regulation in LaNbO₄-based fergusonite to implement high-temperature phase transition and promising dielectric properties

High-entropy effect is a novel design strategy to optimize properties and explore novel materials. In this work, (La_1/5Nd_1/5Sm_1/5Ho_1/5Y_1/5)NbO₄ (5RNO) high-entropy microwave dielectric ceramics were successfully prepared in the sintering temperature range of 1210-1290 ℃ via the solid-phase reaction route, and medium-entropy (3RNO and 4RNO) ceramics were compared. The effects of entropy on crystal structure, phase transition, and dielectric performances were evaluated. Entropy increase yields a significant increase in the phase transition temperature (from monoclinic fergusonite to tetragonal scheelite structure). Optimal microwave dielectric properties were achieved in the high-entropy ceramics (5RNO) at the sintering temperature of 1270 °C for 4 h with a relative density of 98.2%, and microwave dielectric properties of ε_r = 19.48, Q×f = 47,770 GHz, τ_f = -13.50 ppm/°C. This work opens an avenue for the exploration of novel microwave dielectric materials and property optimization via entropy engineering.