  Barium sodium niobate Ba$_2$NaNb$_5$O$_{15}$ (BNN) ceramics with different
amounts of BaO-Na$_2$O-Nb$_2$O$_5$-P$_2$O$_5$ (BNNP) glass were prepared via
the conventional solid-state method. The effect of glass content on the
structural, microstructure, and dielectric properties of BNN ceramics was
investigated. The XRD results showed that no secondary phase was formed after
adding BNNP glass. It was found that such additions reduce the average grain
size and refine the microstructure of the obtained ceramics. Moreover, the
samples exhibited a stable dielectric constant over the temperature range of
25$^\circ$C-150$^\circ$C, and their dielectric constants were significantly
improved. The ceramic with 7.5 wt% BNNP glass content showed a dielectric
constant which is more than twice as much as that of pure BNN ceramic, as well
as a low dielectric loss of less than 5%.
