Large piezoelectricity in NaNbO-based lead-free ceramics tuning oxygen octahedral tilt.

The development of high-performance lead-free piezoceramics for replacing Pb-based perovskites has attracted lots of attention, and comparable room-temperature piezoresponse has been realized in (Na,K)NbO and BaTiO-based ceramics with local structure heterogeneity adjusting polymorphic phase boundary. In this work, a new method of oxygen octahedron tilt design is used in NaNbO-based lead-free ceramics, which usually shows complex oxygen octahedron tilt information inherited from NaNbO. The substitution of Ba(FeNb)O and BaTiO with high tolerance factor into NaNbO leads to a gradual elimination of anti-parallel cation displacement and anti-phase tilt along the three axes; as a result, a single tetragonal phase with 4 space group and only in-phase tilt along axis is achieved in 0.88NaNbO-0.04Ba(FeNb)O-0.08BaTiO ceramic. Accompanying the decreased oxygen octahedral tilt degree, a drastically improved up to 367 pC N (over ten times that of NaNbO ceramic) is obtained, reaching a record high in NaNbO-based lead-free ceramics. Together with temperature insensitive piezoresponse originating from thermally stable oxygen octahedral tilt structure, the studied NaNbO-based materials show large potential for replacing Pb-based ceramics in some electronic devices. The oxygen octahedron tilt engineering would be used for designing more high-performance lead-free ceramics with high piezoresponse and excellent thermal stability simultaneously.