Comparative study on microstructure and electrical properties of (K_0.5Na_0.5)NbO₃ lead-free ceramics prepared via two different sintering methods

Two different sintering methods, i.e., a hot-press sintering method and a conventional sintering method, were utilized to prepare (K_0.5Na_0.5)NbO₃ lead-free piezoelectric ceramics. Microstructure, dielectric, ferroelectric, and piezoelectric properties of the ceramics obtained via the two methods were comparatively studied. Both the ceramics exhibit a single orthorhombic phase. The ceramic via the conventional sintering method shows micron-sized grains and poor densification with many pores. By means of the hot-press sintering, the mean size of grains decreases to 0.1 μm and relative density increases to 96%. The evolution of domains with electrical field was detected via a scanning probe microscope, indicating field-induced domain switching on the microscale. Compared to the conventional sintering, the hot-press sintering causes an increase in the dielectric constant from 183 to 830, remnant polarization from 8.5 to 17.3 μC cm⁻², piezoelectric constant from 60 to 120 pC N⁻¹, and helps a decrease in the dielectric loss from 0.46 to 0.02, coercive field from 20 to 16 kV cm⁻¹. The hot-press sintering facilitates improving the electrical properties of the (K_0.5Na_0.5)NbO₃ ceramic.