Entropy regulation in LaNbO<sub>4</sub>-based fergusonite to implement high-temperature phase transition and promising dielectric properties
Deqin Chen, Na Yan, Xuefeng Cao, Fengrong Li, Laijun Liu, Qinghua Shen, Huanfu Zhou, Chunchun Li
Abstract
High-entropy effect is a novel design strategy to optimize properties and explore novel materials. In this work, (La<sub>1/5</sub>Nd<sub>1/5</sub>Sm<sub>1/5</sub>Ho<sub>1/5</sub>Y<sub>1/5</sub>)NbO<sub>4</sub> (5RNO) high-entropy microwave dielectric ceramics were successfully prepared in the sintering temperature (S.T.) range of 1210–1290 ℃ via a solid-phase reaction route, and medium-entropy (La<sub>1/3</sub>Nd<sub>1/3</sub>Sm<sub>1/3</sub>)NbO<sub>4</sub> and (La<sub>1/4</sub>Nd<sub>1/4</sub>Sm<sub>1/4</sub>Ho<sub>1/4</sub>)NbO<sub>4</sub> (3RNO and 4RNO) ceramics were compared. The effects of the entropy (<i>S</i>) 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 ℃ for 4 h with a relative density of 98.2% and microwave dielectric properties of dielectric permittirity (<i>ε</i><sub>r</sub>) = 19.48, quality factor (<i>Q</i>×<i>f</i>) = 47,770 GHz, and resonant frequency temperature coefficient (<i>τ</i><sub>f</sub>) = –13.50 ppm/℃. This work opens an avenue for the exploration of novel microwave dielectric material and property optimization via entropy engineering.