High-entropy microwave dielectric ceramic (CaSrNaBiLiY)1/6MoO4 with an ultra-low sintering temperature

Abstract

Dielectric ceramics with low sintering temperatures and superior performances are essential for electronic device applications. However, it is challenging to obtain glass-free microwave dielectric ceramics with ultra-low sintering temperatures. Herein, we introduce a low-firing high-performance scheelite ceramic, (CaSrNaBiLiY)_1/6MoO₄, using high-entropy design to manipulate the grain boundary energy and reduce the intrinsic sintering temperature. A single phase high-entropy ceramic with tetragonal scheelite structure is formed in (CaSrNaBiLiY)_1/6MoO₄, as demonstrated by X-ray diffraction and transmission electron microscopy analyses. (CaSrNaBiLiY)_1/6MoO₄ shows an ultra-low sintering temperature of 580°C, good microwave dielectric properties with a permittivity of 21.1, a Q × f value of 10 200 GHz, and a temperature coefficient of resonant frequency value of 43.7 ppm/°C, and excellent chemical compatibility with Ag/Al electrode materials. The influences of high entropy on sintering temperatures and performances are discussed from the perspective of thermodynamic laws and lattice distortion effects. The grain boundary region with a thickness of ∼10 nm is rich in Ca element and the lattice distortion from multiple cations in A site increases the permittivity of high-entropy ceramics. The microwave dielectric properties of (CaSrNaBiLiY)_1/6MoO₄ are mainly derived from polarized optical phonons. This work provides a route for the development of glass-free ceramics with reduced sintering temperatures using high-entropy design.