Structure and chemical bond characteristics of two low-ε microwave dielectric ceramics LiBO2 (B = Ga, In) with opposite τ

MSO4 (M = Ca, Sr, Ba) microwave dielectric ceramics with low dielectric constant

“…The low ε r , high Qf value, and near‐zero τ f , W of BaSO 4 ceramic indicate that it is a promising candidate as millimeter‐wave dielectric ceramics, and the low sintering temperature also reveals its attraction for low‐temperature cofired ceramic technology. Besides, SrSO 4 ceramic has a large positive τ f , W of 101.6 ppm/°C, which is also unusual in low‐ ε r single‐phase microwave dielectric ceramics that are usually of large but negative τ f 1,15–18 . Therefore, SrSO 4 may be applicable as a compensator for adjusting the negative τ f of low‐ ε r ceramics to near‐zero.…”

“…Therefore, it is an important issue to explore the single‐phase microwave dielectric ceramics with low ε r and near‐zero τ f . Besides, single‐phase microwave dielectric ceramics with low ε r and positive τ f are rare, and they may be better compensators for adjusting τ f to near‐zero than those with high ε r and positive τ f , as the increase in ε r of the composites is expected to be suppressed 15–18 …”

“…Besides, single-phase microwave dielectric ceramics with low ε r and positive τ f are rare, and they may be better compensators for adjusting τ f to near-zero than those with high ε r and positive τ f , as the increase in ε r of the composites is expected to be suppressed. [15][16][17][18] Microwave dielectric ceramics with strong covalent bonds tend to exhibit low dielectric constant, 6,19,20 as the dielectric constant of low-loss microwave dielectric ceramics originates from the intrinsic polarization mechanisms, including ionic polarization and electronic polarization, and the former can greatly be suppressed by the strong covalent bonds. In the past years, a lot of low-ε r oxide microwave dielectric ceramics rich in nonmetallic elements with strong covalent bonds between nonmetallic cations and O 2− have been explored, such as SiO 2 polymorphs, borates, silicates, and phosphates, 5,6,8,[19][20][21][22][23][24][25][26][27][28][29] as shown in Table 1.…”

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

“…[1][2][3] In previous work, a low sintering characteristic LiInO 2 microwave dielectric ceramic with a α-LiFeO 2 tetragonal structure phase was obtained, exhibiting a relative density of 85.6% and microwave dielectric properties of ε r (∼9.6), Q × f (∼39 600 GHz), and τ f (∼ 9.8 ppm/ • C). 4 And to eliminate the effect of pores on microwave dielectric properties, LiF was selected as an additive to improve the density, and favorable microwave dielectric properties (ε r = 13.6, Q × f = 52 500 GHz, τ f = +18.1 ppm/ • C) were obtained in LiInO 2 +3 wt.% LiF ceramic sintered at 890 • C. 5 To best of our knowledge, low ε r microwave dielectric materials usually possess a negative τ f . Thus, LiInO 2 ceramic with a low ε r and a positive τ f is an abnormal phenomenon, and the intrinsic mechanisms are necessary to investigate.…”

“…In previous work, the Phillips-Van Vechten-Levine chemical bond theory and bond valence were used to investigate the bond ionicity and bond valence of In-O and Li-O bonds in LiInO 2 ceramic, indicating that the τ f is closely related to the rattling effect of cations. 4,5 On F I G U R E 1 Crystal structure of (A) LiInO 2 and (B) LiInO 2 ceramic. the other hand, Harrop et al 6,7 have reported that the τ f of microwave dielectric materials can be regulated by the dilution of the average ionic polarizability.…”