The relationship between crystal structure and modified microwave dielectric properties of Ca₃SnSi_2‐xGe_xO₉ ceramics

Abstract

Ca3SnSi2‐xGexO9 (0 ≤ x ≤ 0.8) and (1–y) Ca3SnSi1.6Ge0.4O9 – y CaSnSiO5 – 2 wt% LiF (y = 0.4 and 0.5) microwave dielectric ceramics were prepared by traditional solid‐state reaction through sintering at 1250°C–1425°C for 5 h and at 875°C for 2 h, respectively. Ge4+ replaced Si4+, and Ca3SnSi2‐xGexO9 (0 ≤ x ≤ 0.4) solid solutions were obtained. At 0.1 ≤ x ≤ 0.4, the Ge4+ substitution for Si4+ decreased the sintering temperature of Ca3SnSi2‐xGexO9 from 1425 to 1300°C, the SnO6 octahedral distortions, and the average CaO7 decahedral distortions, which affected the τf value. The large average decahedral distortions corresponded with nearer‐zero τf values at Ca3SnSi2‐xGexO9 (0.1 ≤ x ≤ 0.4) ceramics. The τf value and sintering temperature of Ca3SnSi2‐xGexO9 (x = 0.4) ceramic were adjusted to near‐zero by CaSnSiO5 and decreased to 875°C upon the addition of 2 wt% LiF. The (1 – y) Ca3SnSi1.6Ge0.4O9 – y CaSnSiO5 – 2 wt% LiF (y = 0.5) ceramic sintered at 875°C for 2 h exhibited good microwave dielectric properties: εr = 10.3, Q × f = 14 300 GHz (at 12.2 GHz), and τf = ‒5.8 ppm/°C.

Phase composition, crystal structure, and microwave dielectric properties of LiIn1‐xAlxO2 ceramics

“…Generally, ionic substitution was used to enhance the density, regulate the crystal structure and phase transition, and thus to optimize their microwave dielectric properties of ceramics. [8][9][10][11][12][13][14] For example, in the Li 2 Sn 1-x Ge x O 3 system, 11 appropriate Ge 4+ substitution for Sn 4+ could slightly lower the sintering temperature from 1325 • C (x = 0) to 1175 • C (x = 0.7), increase the average grain sizes, decrease the porosity, and improve their microwave dielectric properties simultaneously. In the SmNb 1-x V x O 4 system, 14 the V 5+ substitution for Nb 5+ could induce the phase transition of monoclinic fergusonite to tetragonal zircon phase, while effectively reducing the phase transition temperature.…”

“…Therefore, the intrinsic mechanisms of τ f in LiInO 2 ceramic can be investigated based on the rattling effect of cations and the dilution of the average ionic polarizability. Generally, ionic substitution was used to enhance the density, regulate the crystal structure and phase transition, and thus to optimize their microwave dielectric properties of ceramics 8–14 . For example, in the Li 2 Sn 1‐ x Ge x O 3 system, 11 appropriate Ge 4+ substitution for Sn 4+ could slightly lower the sintering temperature from 1325°C ( x = 0) to 1175°C ( x = 0.7), increase the average grain sizes, decrease the porosity, and improve their microwave dielectric properties simultaneously.…”