Poling and depoling influence on the micro-stress states and phase coexistence in KNN-based piezoelectric ceramics

Abstract

In this work a microstructural qualitative and quantitative study of spatial stress distributions in modified KNN ceramics (K0.44Na0.52Li0.04)1-xCox/2 (Nb0.86Ta0.10Sb0.04)O3, according to the polarization state is shown. X-ray diffraction reflects a perovskite crystalline structure with coexistence of Tetragonal and Orthorhombic phases (T/O). Confocal Raman microscopy shows that these crystalline phases are distributed in randomly micrometric regions through the ceramic volume. Tetragonal regions show higher piezoelectric coefficient and exhibit a higher micro-stress that hardens the ferroelectric response. By the contrary, the occurrence of orthorhombic micro-regions softened the ferroelectric behavior and reduced their piezoelectric coefficients. The ferroelectric response of ceramics is studied, where poling is also shown as a factor that affects the spatial micro-stress distributions. Finally, a model that relates the results obtained by Raman characterization with the ferroelectric properties and stress states is proposed.