Role of Cu and Y in sintering, phase transition, and electrical properties of BCZT lead-free piezoceramics

Lead-free (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3-xwt%CuOywt%Y2O3 (BCZT-CuxYy) ceramics with high piezoelectricity were synthesized by the conventional solid-state reaction method. The role of Cu and Y (Cu/Y) in sintering, phase transition, and electrical properties of such ceramics was systematically studied. The results indicated that the sintering temperatures of BCZT-CuxYy decreased by at least 100 °C due to the low melting point of CuO. The promotion effect of Cu/Y on phase transition lied in the improvement of TC by 5-15 °C and the coexistence of O+T phase near room temperature. The contribution of Cu/Y to electrical properties was mainly ascribed to the grains growth, the formed oxygen vacancies and lattice distortions, and the donor doping effect of Y3+. Adding 0.10 wt% Cu2+ and 0.06 wt% Y3+ into BCZT dramatically improved the electrical properties as following: d33 = 552 pC/N, εm = 10175, εr = 4546, tanδ = 0.016, TC = 100 °C, kp = 0.475, Qm = 157.2, Pr = 10.82 μC/cm2 and EC = 2.33 kV/cm. A plausible mechanism was obtained to explain the reaction process and the favorable performances of BCZT-CuxYy. Co-doping Cu2+ and Y3+ into BCZT could be a promising method to improve and balance the sintering, phase transition, and electrical properties for potential practical applications of lead-free piezoceramics.