Grain Growth Behavior and Electrical Properties of 0.96(K(0.46−x)Na(0.54−x))Nb(0.95)Sb(0.05)O(3)–0.04Bi(0.5)(Na(0.82)K(0.18))(0.5)ZrO(3) Ceramics

This study investigated the causes of microstructural changes and the resultant electrical properties according to the sintering temperature of 0.96(K(0.46−x)Na(0.54−x))Nb(0.95)Sb(0.05)O(3)-0.04Bi(0.5)(Na(0.82)K(0.18))(0.5)ZrO(3) lead-free ceramics by analyzing the correlation between vacancy concentrations and 2D nucleation. When sintered for 4 h, no grain growth occurred for the x = 0.000 composition over a wide temperature range, demonstrating that the existence of initial vacancies is essential for grain growth. As x increased, that is, as the vacancy concentration increased, the critical driving force (ΔG(C)) for 2D nucleation decreased, and abnormal grain growth was promoted. The number and size of these abnormal grains increased as the sintering temperature increased, but at sintering temperatures above 1100 °C, they decreased again owing to a large drop in ΔG(C). The x = 0.005 specimen sintered at 1085 °C exhibited excellent piezoelectric properties of d(33) = 498 pC/N and k(p) = 0.45 due to the large number of large abnormal grains with an 83% tetragonal phase fraction. The x = 0.000 specimen sintered at 1130 °C with suppressed grain growth exhibited good energy storage properties because of its very high relative density and small grain size of 300 to 400 nm.