Microwave dielectric characteristics of tungsten bronze-type Ba4Nd28/3Ti18-yGa4y/3O54 ceramics with temperature stable and ultra-low loss

Abstract

A series of high-k Ba4Nd28/3Ti18-yGa4y/3O54 (0≤y≤2, BNTG) ceramics with temperature stable and ultra-low dielectric loss were synthesized via the conventional solid-state reaction. The main phase of all BNTG ceramics demonstrated an orthorhombic tungsten-bronze structure, but the impurity phase (gallium-rich phase) was found in BNTG (y = 2) ceramic. Partial substitution of Ga3+ for Ti4+ in B-site was a valid method to improve the temperature stability and dielectric loss of BNTG ceramics. The variation of εr values of BNTG ceramics was dominated by the ionic polarizability. The ultra-low dielectric loss (ultra-high Q × f values) was associated with grain size, suppression of Ti3+ and impurity phase. The decrease of TCF values was highly dependent on the tilting of Ti-O octahedra and impurity phase. Finally, outstanding combination dielectric characteristics were achieved for BNTG microwave ceramics at y = 1.5 (εr = 72.8, Q × f = 14,600 GHz, TCF=+4.1 ppm/°C) and at y = 2 (εr = 70.3, Q × f = 15,500 GHz, TCF=+3.9 ppm/°C).