  A series of (1-x)[(2BaO-0,5Na2O)-1P2O5] -xNb2O5 (BNPN, x=0,41, 0,43, 0,45,
0,48) glass-ceramics based on phosphate glasses have been prepared via a
controlled-crystallization route. The structure, dielectric properties,
interfacial polarization, and energy storage properties were systematically
investigated. The x-ray diffraction results showed the simultaneous presence of
Ba2NaNb5O15 tungsten bronze structure (TTB) and the NaNbO3 perovskite. A stable
dielectric constant over a temperature range from 25-200{\deg}C, low dielectric
losses less than 0,03, and excellent frequency stability at room temperature
were obtained. The decrease in niobium content promoted TTB crystallization
with the improvement of the high dielectric properties of the system. The
optimum of the dielectric constant and recoverable energy storage density were
obtained for BNP41 crystallized at 1000{\deg}C. Analyses of the complex
impedance indicated that the niobium content and crystallization temperature
affect the interfacial polarization.
