Piezoelectric, ferroelectric and mechanical properties of Li-doped PNN-PHT ceramics

Piezoelectric ceramics are widely used in aviation, aerospace, communications, weapons, electronics and other high-tech fields. This study focuses on high piezoelectric Pb(Nb_2/3Ni_1/3)O₃-Pb(Hf_1/2Ti_1/2)O₃ (PNN-PHT) binary ceramic as the research matrix. By doping Li₂CO₃, the Curie temperature is increased, and the effects of doping concentration on microstructure, phase structure, and electrical performances of the ceramics are discussed. The study found that all ceramics were rhombohedral -tetragonal mixed phases, and no impurity phases were generated. When x = 0.20, the samples have the best mass density ρ = 8.0291 g/cm³, the best piezoelectric constant d₃₃ = 702 pC/N, the largest signal piezoelectric constant d₃₃* = 943 pm/V, the largest strain value S = 0.56%, the highest electromechanical coupling coefficient k_p = 51.9%, excellent hardness H = 4.5221 GPa and fracture toughness K_IC = 1.06 MPa•m^0.5, and a higher Curie temperature T_C = 155 ^oC. At the same time, the x = 0.20 sample has excellent temperature stability in 20 ~ 150 ^oC, achieving a balance and compromise between piezoelectric properties and temperature stability.