Insight For The Construction of R-T Phase Boundary in KNN Piezoceramics From The View of Energy Band Structure

The crystal structures and associated energy band structures of classic lead-based PZT (PbZr 0.5 T i0.5 O 3 ) and lead-free KNN (K 0.5 Na 0.5 NbO 3 ) piezoelectric ceramics prepared by a solid-state method are systematically studied based on the First-principles calculations. For better understanding relations between energy band structures and the phase structures in the PZT and KNN, the components PT (PbT i O 3 )/PZ (PbZrO 3 ) and KN (KNbO 3 )/NN (NaNbO 3 ) are also calculated. The results suggest that the vital contribution to R-T morphotropic phase boundary (MPB) in PZT comes from the hybridization of A-site and B-site ions, which causes stretching and tilting of oxygen octahedron and therefore leads to the formation of R and T phases. The KNN behaves differently. Moreover, it’s concluded that the band structure highly inherited from tetragonal PT plays an important role in the construction of the R-T phase boundary according to the comparison of PZT and KNN. In general, the work inspires an idea from the view of energy band structure to realize R-T phase coexistence as well as improved piezoelectric properties in KNN-based lead-free piezoceramics.