Structural, microstructural and electrical properties evolution of (K,Na,Li)(Nb,Ta,Sb)O3 lead-free piezoceramics through NiO doping

Excellent piezoelectric properties have been reported in the (K,Na)NbO3–LiTaO3–LiSbO3 system and have been regarded as a new candidate of lead-free piezoelectric material. Nevertheless, there are still some structural and electrical aspects that remain controversial with respect to the role of dopants in this system. NiO doping modifies the (K,Na,Li)(Nb,Ta,Sb)O3 structure, giving rise to the appearance of the TTB-like secondary phase and to changes on the orthorhombic to tetragonal phase transition temperature. The microstructural characterization reveals that sintering process is assisted by a transient liquid phase. The presence of Ni in the liquid phase indicates that NiII ions could act as new nucleus for the secondary phase crystallization. Thus, as higher the amounts of liquid phase, higher the secondary phase appearance. The modifications on the structure and microstructure of the system cause a reduction of the piezoelectric constant, which is accompanied by an increase on the mechanical quality factor.