Crystal structural dependence of microwave dielectric characteristics of novel BaM2N3O10 trisilicate ceramics
Kang Du, Zheyu Liu, Tailai Wen, Mengdie Zhou, Changzhi Yin, Yiyang Cai, Mingfei Cheng, Gang Wang, Wei Zhu, Shengxiang Wang, Wen Lei
Abstract
The crystal structure, phase compositions and microwave dielectric properties of the novel Ba M 2 N 3 O 10 ( M = Sc, Yb, Er, Y, Ho and Gd; N = Si and Ge) ceramics were investigated. Single-phase compositions could be obtained in Ba M 2 Si 3 O 10 ( M = Sc, Yb, Er, Y, Ho and Gd) and Ba M 2 Ge 3 O 10 ( M = Sc, Yb, Er, Y and Gd) ceramics, and the small content of second phase existed in the BaHo 2 Ge 3 O 10 ceramic. The monoclinic crystal structure with the P 2 1 /m space group of Ba M 2 N 3 O 10 ( M = Sc, Yb, Er, Y, Ho and Gd; N = Si and Ge) ceramics was confirmed via selected-area electron diffraction and Rietveld refinement . The Phillips-Van Vechten-Levine (P-V-L) theory, Clausius-Mossotti (C-M) equations and bond valence theory were used to reveal the relationships between the crystal structural parameters and microwave dielectric properties of Ba M 2 N 3 O 10 ceramics. The ε r-exp of Ba M 2 N 3 O 10 ceramics was significantly affected by ionic polarisability and relative density, and the C-M equations rather than P-V-L theory were more suitable for evaluating the theoretical permittivity of Ba M 2 N 3 O 10 trisilicate ceramics. The Q × f values of Ba M 2 N 3 O 10 ceramics were mainly related to the total lattice energy , and the large total lattice energy corresponded to the high Q × f values. The average bond valence of N -O bonds and M O 6 octahedral distortion played an important role in controlling the τ f values of Ba M 2 N 3 O 10 ceramics. The high − V N and large M O 6 octahedral distortion corresponded to the small |τ f | values of Ba M 2 N 3 O 10 ceramics. A low permittivity (8.8), an ultra-high Q × f value (95,601 GHz) and a small negative τ f value ( 28.2 ppm/°C) were obtained in the novel BaYb 2 Si 3 O 10 ceramic when sintered at 1400 °C for 5 h.