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

Abstract

In this work, a series of V-modified Ba 3 Ta 4 Ti 4 O 21 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 BaTa 2 O 6 was formed with x increasing further. In the Ba 3 Ta 4-x V x Ti 4 O 21 (0-0.6) system, the V 5+ substitution for Ta 5+ exhibited a significantly reduction in sintering temperature (1350 to 1150 o C), and a slightly change in lattice parameter. Bond valence theory demonstrated that the V 5+ substitution for Ta 5+ resulted a more strength rattling effect for Ti 4+ and Ta 5+ , which might be a key factor for the large deviation between ε r and ε th . Moreover, the intrinsic dielectric properties of Ba 3 Ta 4- x V x Ti 4 O 21 ( x = 0.2, 0.4, 0.6) ceramics were investigated by infrared reflectivity spectra, indicating that replacing Ta 5+ by V 5+ can reduce the dielectric loss. And the optimum dielectric performances were obtained at x = 0.6 ( ε r ~ 44.4, Q × f = 13,800 GHz, τ f ~ + 60.3 ppm/°C) sintered at 1150 o C for 6 h.