Rattling effects on microwave dielectric properties of Ca3TiBGe3O12 (B = Mg, Zn) garnets

作者：Yang, Yang; Zhai, Yifan; Xiang, Huaicheng; Li, Jie; Tang, Ying^*; Fang, Liang^*

来源：Journal of the European Ceramic Society, 2022, 42(11): 4566-4572.

DOI：10.1016/j.jeurceramsoc.2022.04.054

• Garnet structure
• Microwave dielectric properties
• Bond valence
• Rattling effect

Herein two cubic garnet ceramics Ca3TiBGe3O12 (B = Mg, Zn) were prepared with optimal sintering temperatures of 1300 C and 1200 C, respectively. Both ceramics exhibited promising microwave dielectric properties as well as rather low coefficient of thermal expansion (alpha(L)) of epsilon(r) =11.95, Qxf = 83,000 GHz, tau(f )=-34.1 ppm/C and alpha L = 3.9 ppm/C for Ca3TiMgGe3O12, and epsilon r = 11.80, Qxf = 79,000 GHz, tau(f)=-42.9 ppm/C and alpha(L) = 4.0 ppm/ C for Ca3TiZnGe3O12. Bond valence calculation reveals that Ca2+ at the A-site is slightly compressed, Ge4+ at C site is rattling, and compressed Mg2+/Zn2+ coexists with rattling Ti4+ in the B-site. The large positive deviations (17.22% for Ca3TiMgGe3O12 and 10.90% for Ca3TiZnGe3O12) between the porosity corrected epsilon(r(Corr)) (12.32 and 12.41) and calculated epsilon(r(C-M)) (10.51 and 11.19) by the C-M equation were observed, which might be attributed to the combination of rattling effects in B-site and C-site. The relatively stronger rattling effect in Ca3TiMgGe3O12 leads to a higher epsilon r and a tau f closer to zero than those of Ca3TiZnGe3O12. Besides, the Qxf values of Ca3TiBGe3O12 (B = Mg, Zn) ceramics are mainly affected by relative density, packing fraction, and Raman mode (A(1 g)).

• 单位
  广西大学; y; 桂林理工大学