Liquid‐phase sintering, microstructural evolution, and microwave dielectric properties of Li₂Mg₃SnO₆–LiF ceramics

Abstract

The liquid‐phase sintering behavior and microstructural evolution of x wt% LiF aided Li2Mg3SnO6 ceramics (x = 1‐7) were investigated for the purpose to prepare dense phase‐pure ceramic samples. The grain and pore morphology, density variation, and phase structures were especially correlated with the subsequent microwave dielectric properties. The experimental results demonstrate a typical liquid‐phase sintering in LiF–Li2Mg3SnO6 ceramics, in which LiF proves to be an effective sintering aid for the Li2Mg3SnO6 ceramic and obviously reduces its optimum sintering temperature from ~1200°C to ~850°C. The actual sample density and microstructure (grain and pores) strongly depended on both the amount of LiF additive and the sintering temperature. Higher sintering temperature tended to cause the formation of closed pores in Li2Mg3SnO6‐x wt% LiF ceramics owing to the increase in the migration ability of grain boundary. An obvious transition of fracture modes from transgranular to intergranular ones was observed approximately at x = 4. A single‐phase dense Li2Mg3SnO6 ceramic could be obtained in the temperature range of 875°C‐1100°C, beyond which the secondary phase Li4MgSn2O7 (<850°C) and Mg2SnO4 (>1100°C) appeared. Excellent microwave dielectric properties of Q × f = 230 000‐330 000 GHz, εr = ~10.5 and τf = ~−40 ppm/°C were obtained for Li2Mg3SnO6 ceramics with x = 2‐5 as sintered at ~1150°C. For LTCC applications, a desirable Q × f value of ~133 000 GHz could be achieved in samples with x = 3‐4 as sintered at 875°C.

Low‐temperature sintering of microwave ceramics with high Qf values through LiF addition

“…But the preparation of the raw CaMgSi 2 O 6 glass needs a high temperature (~1500°C) and the final glass‐ceramics generally yields low Qf values . LiF, which has a low melting point (~848°C), is often utilized in the development of low‐temperature fired dielectric ceramics, such as Li 2 Mg 3 SnO 6 , BaTiO 3 , BaFe 0.5 Nb 0.5 O 3 , MgO and Ba(Mg 1/2 W 1/2 )O 3 ‐TiO 2 system, for LTCC applications . Through moderate LiF addition, low‐sintering temperature and excellent microwave dielectric properties were achieved simultaneously in these dielectric ceramics.…”

Li2+xZrO3Fx (0 ≤ x ≤1.25): A new high‐Q × f and temperature‐stable microwave dielectric ceramic system for LTCC applications

“…Considering the sintering temperature, MDPs, and chemical compatibility with Ag electrode, the Li 2+ x ZrO 3 F x ceramics are undoubtedly promising LTCC candidate materials. LiF is usually used as a sintering additive for MDCMs, as it is simply expected to provide liquid phase at elevated temperatures and accelerate the densification process of the ceramic samples 46–48 . In the present work, we succeeded in the optimization of the sinterability and MDPs of L 2 ZrO 3 by the use of LiF, which acts as a key member of the binary solid solution system of L 2 ZrO 3 ‐LiF with a rock‐salt structure.…”

“…LiF is usually used as a sintering additive for MDCMs, as it is simply expected to provide liquid phase at elevated temperatures and accelerate the densification process of the ceramic samples. [46][47][48] In the present work, we succeeded in the optimization of the sinterability and MDPs of L 2 ZrO 3 by the use of LiF, which acts as a key member of the binary solid solution system of L 2 ZrO 3 -LiF with a rock-salt structure. Therefore, further study can focus on exploring more new LiF-containing rock-salt-structured ceramic systems with excellent MDPs.…”

Sc Modification Induced Short-range Ordering in ZnGa2O4&nbsp;Spinel Leading to High Microwave Dielectric Performance

“…This type of crystal structure has a great variability because of variety cation selections, and possibilities in cation ordering such as common spinel (AB2O4), inverse spinel (B(AB)O4) and mixed-type spinel. So far, spinel structured ceramics for high frequency application include M2SnO4 [13][14], M2SiO4 [15][16], MAl2O4 (M=Zn, Mg) [17][18] and MGa2O4 (M = Zn, Mg) [19][20][21][22][23].…”