Influence of milling speed of high energy mechanochemical technique on microstructure and electrical properties of K_0.5Na_0.5NbO₃ ceramics

The preparation of K_0.5Na_0.5NbO₃ (KNN) ceramics with submicron grain size and higher density was accomplished by adjusting the high energy ball milling process’s parameters, considerably enhancing the preparation efficiency and the electrical properties of ceramics. Different rotation speed of high energy ball milling have a significant impact on the electrical properties and microstructure of ceramics, but little impact on the phase structure of ceramics. Pure KNN ceramics can be obtained at 325–800 rpm of milling speed, showing a typical orthorhombic symmetry at room temperature with an average grain size of 0.21 μm at the milling speed of 600 rpm and sintering temperature of 1140 °C. It also has a good electric characteristics and increased energy storage density at the rotation speed of 600 rpm, i.e., the total energy storage density (W_tol = 3.79 J/cm³) were 91% greater than the KNN by traditional methods, it can be mainly ascribed to the large P_max (62 µC/cm²) and dielectric breakdown strength (E_DBS = 110 kV/cm). Moreover, the dielectric and ferroelectric properties of the optimized KNN ceramics exhibit strong dependence on the particle size of the initial powders. This results shown that the optimization milling speed of high energy ball milling are helpful to achieve dense ceramics with outstanding electrical properties, thus significantly enhancing the preparation efficiency and the energy storage properties of KNN-based ceramics.