Improved piezoelectricity in ternary potassium-sodium niobate lead-free ceramics with large strain
Although potassium-sodium niobate (KNN)-based ceramics with good piezoelectric performance have been obtained by phase engineering strategy, a low electric field-induced strain (<0.2%) even applying large electric fields is observed in the ceramics prepared by normal sintering, which hardly satisfies practical applications demands. Here, a ternary lead-free material system of (0.965-x)K0.5Na0.5Nb0.975Sb0.25O3-0.035Bi0.5Na0.5ZrO3-xBiFeO3 (KNNS-BNZ-xBF, 0 ≤ x ≤ 0.008) ceramics with excellent overall performance has designed, aiming to achieve the balanced development between piezoelectric and strain property. A systematic study about phase structure, electric properties and temperature stability is carried out in the ceramics, and the optimal electric properties (eg., d33 ≈ 511 pC/N, Suni ≈ 0.202%, d33* ≈ 505 pm/V, and Tc ≈ 269 oC) are obtained at x=0.007 owing to the large tetragonality and R-T phase structure with low polarization anisotropy as well as weak energy barriers. Moreover, a new approach used to evaluate coercivity (Ec) qualitatively provides more choices to identify Ec in ferroelectrics. We believe that it may promote the application process of lead-free piezoelectric materials.