Effect of V5+ substitution for Ta5+ on the bond valence, structure and microwave dielectric properties of Ba3Ta4Ti4O21 ceramics

In this work, a series of V-modified Ba3Ta4Ti4O21 microwave dielectric ceramics were obtained by a solid-state reaction method. XRD combined with Rietveld refinement confirmed that a single phase can be remained within x value of 0-0.6, and a secondary phase BaTa2O6 was formed with x increasing further. In the Ba3Ta4_xVxTi4O21 (0-0.6) system, the V5+ substitution for Ta5+ exhibited a significantly reduction in sintering temperature (1350-1150 degrees C), and a slightly change in lattice parameter. Bond valence theory demonstrated that the V5+ substitution for Ta5+ resulted a more strength rattling effect for Ti4+ and Ta5+, which might be a key factor for the large deviation between er and eth. Moreover, the intrinsic dielectric properties of Ba3Ta4-xVxTi4O21 (x = 0.2, 0.4, 0.6) ceramics were investigated by infrared reflectivity spectra, indicating that replacing Ta5+ by V5+ can reduce the dielectric loss. And the optimum dielectric performances were obtained at x = 0.6 (er -44.4, Q x f = 13,800 GHz, if -+ 60.3 ppm/degrees C) sintered at 1150 degrees C for 6 h.