Giant Piezoelectricity and High Curie Temperature in Nanostructured Alkali Niobate Lead-Free Piezoceramics through Phase Coexistence

Abstract

Because of growing environmental concerns, the development of lead-free piezoelectric materials with enhanced properties has become of great interest. Here, we report a giant piezoelectric coefficient ( d 33 ) of 550 pC/N and a high Curie temperature ( T C ) of 237 °C in (1– x – y )K 1– w Na w Nb 1– z Sb z O 3– x BiFeO 3– y Bi 0.5 Na 0.5 ZrO 3 (KN w NS z - x BF- y BNZ) ceramics by optimizing x, y, z, and w . Atomic-resolution polarization mapping by Z-contrast imaging reveals the intimate coexistence of rhombohedral (R) and tetragonal (T) phases inside nanodomains, that is, a structural origin for the R–T phase boundary in the present KNN system. Hence, the physical origin of high piezoelectric performance can be attributed to a nearly vanishing polarization anisotropy and thus low domain wall energy, facilitating easy polarization rotation between different states under an external field.