Effect of Na/K ratio on structure evolution, dielectric and energy storage properties of potassium sodium niobate-based borate glass-ceramics

Abstract

To reduce carrier mobility and optimize crystal phase species, 0.9((1-x)K2O-xNa2O-Nb2O5)-0.1B2O3 glass-ceramics were prepared by the traditional melting method. By introducing Na2O, Na0.9K0.1NbO3 ferroelectric phase increases, and the “rice-like” morphology grains transfer to the cubic grains gradually. As the radius of Na+ is smaller than K+, the ability of Na+ to provide free oxygen is weaker, which reduces the fracture degree of [BO3] and makes the glass network structure tend to compact. As a result, the stable high permittivity (158) and low dielectric loss (tanδ ≤ 0.04) are obtained in the broad frequency range (20 Hz to 1 MHz) and temperature range (25–200 °C). In addition, these samples also reveal a relatively high energy-storage density (1.64 J/cm3) under breakdown strength (490 kV/cm), which is mainly attributed to the dense glass network and optimized crystalline phase. Pulse discharge testing further verifies that the 0.9(0.5K2O-0.5Na2O-Nb2O5)-0.1B2O3 glass-ceramic achieves high actual energy-storage density (0.09 J/cm3) at lower electric field strengths, and fast charging and discharging speed (τ0.9 = 15 ns).