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, (La1/5Nd1/5Sm1/5Ho1/5Y1/5)NbO4 (5RNO) high-entropy microwave dielectric ceramics were successfully prepared in the sintering temperature (S.T.) range of 1210-1290 degrees C via a solid-phase reaction route, and medium-entropy (La1/3Nd1/3Sm1/3)NbO4 and (La1/4Nd1/4Sm1/4Ho1/4)NbO4 (3RNO and 4RNO) ceramics were compared. The effects of the entropy (S) on crystal structure, phase transition, and dielectric performance were evaluated. The entropy increase yields a significant increase in a 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 degrees C for 4 h with a relative density of 98.2% and microwave dielectric properties of dielectric permittirity (epsilon(r)) = 19.48, quality factor (Qxf) = 47,770 GHz, and resonant frequency temperature coefficient (tau(f)) = -13.50 ppm/degrees C. This work opens an avenue for the exploration of novel microwave dielectric material and property optimization via entropy engineering.