Improvement of the piezoelectric and ferroelectric properties of (K, Na)0.5NbO3 ceramics via two-step calcination–milling route

A second calcination–milling step was introduced in the conventional processing of (K, Na)0.5NbO3 (KNN) ceramics (sintered in air) to further homogenenize the particle size distribution of the pre-sintered powders. The ceramic derived from the powders prepared by the two-step route possesses grains with better uniformity and is more compact. The relative density of the bulk ceramic reached 96.9%. Excellent properties are obtained in as-prepared KNN ceramics with kp=44%, d33=111 pC/N, tanδ=0.85%, ε33T/εo=311, Qm=193, Pr=25.4 μC/cm2, d33⁎=251 pm/V, which are superior to those of the ceramics derived from the powders calcined once as used in the traditional processing. These results indicate that twice-calcination–milling route is shown to be a facile and effective way to simultaneously improve the piezoelectric and ferroelectric properties of KNN ceramics without sintering aids.