Cobalt ions doped PNN-PHT ceramics with excellent piezoelectric properties

In this study, Co-doped 0.49 Pb(Ni_1/3Nb_2/3)O₃-0.51 Pb(Hf_0.3Ti_0.7)O₃ ceramics with high piezoelectric constants, electromechanical coupling coefficients, and low dielectric losses were prepared by conventional solid-phase reaction method for use as piezoelectric energy harvesters in both resonant and non-resonant working states. XRD results showed the dissolution of Co ions in the crystal lattice, thereby replacing B-sites and transforming the crystal phase into tetragonal phase. Valence states of Co obtained from fitted XPS data confirmed the existence of Co as Co²⁺ in the lattice. The introduction of Co²⁺ effectively increased grain size, improved ferroelectric properties, reduced leakage current density, and enhanced electromechanical coupling coefficient k_p. Impacts of Co-doping on properties of the as-obtained ceramics were discussed. The optimal performances were obtained at x = 1.25, with piezoelectric constant d₃₃~780 pC/N, electromechanical coupling coefficient k_p~0.62, and dielectric loss tan δ = 0.78%. In sum, the excellent piezoelectric properties of Co-doped PNN-PHT ceramics look promising for use as piezoelectric energy harvesters.