Structure evolution and τf influence mechanism of Bi1–xHoxVO4 microwave dielectric ceramics for LTCC applications

Bi 1– x Ho x VO 4 (0.1 ≤ x ≤ 0.9) ceramics were prepared via a solid-state reaction method, and all the ceramics could be well densified in the 920–980 °C range. The ceramics with 0.1 ≤ x < 0.4 were composed of both monoclinic scheelite (M) and tetragonal zircon (T) phases, and a single M phase could be obtained in the range of x ≥ 0.4. The measured ε r decreased from 58.9 ( x = 0.1) to 14.7 ( x = 0.9), so do the calculated values ( ε r(C − M) = 34.3–12.1), and the main reason for ε r > ε r(C − M) was the rattling of Ho 3+ in the dodecahedron. Two points with zero τ f appeared in Bi 1 – x Ho x VO 4 (0 ≤ x ≤ 1) ceramics, and the best microwave dielectric properties with ε r = 16.6, Q × f = 18,400 GHz ( f = 10.69 GHz), and τ f = +3.29 ppm/°C were obtained in the Bi 0.2 Ho 0.8 VO 4 ceramic. The change in temperature coefficient of ionic polarizability ( τ αm ) caused by the rattling effect of cations is the physical essence that affects τ f . Therefore, the rattling effect can be used as an effective mechanism to regulate τ f in low- ε r materials. Furthermore, there was no chemical reaction between Bi 1 – x Ho x VO 4 and Ag electrode, which indicates potential applications in low-temperature co-fired ceramic (LTCC) technology.