Effects of ZnO nanoneedles addition on the mechanical and piezoelectric properties of hard PZT-based composites

Hard PZT (PZT4)-based composites embedded by ZnO nanoneedles (denoted as PZT/ZnO_n) were fabricated by a solid state sintering technique. The characteristic diffraction peaks of the perovskite PZT and ZnO phases were identified from the studied composites, indicating the retention of ZnO_n. With increasing ZnO_n content, the grain size of the composites was reduced gradually. In contrast with the pure PZT, the PZT/ZnO_n composites possessed more excellent mechanical properties, while the piezoelectric properties were reduced by a certain extent. The best mechanical properties of PZT/ZnO_n composites were obtained by sintering at 1,150 °C with 1.5 wt% ZnO nanoneedles addition: fracture toughness K _IC ~ 2.04 MPa m^1/2, flexural strength σ _f ~ 105.44 MPa, compressive strength σ _c ~ 543.89 MPa. The piezoelectric properties of the PZT/ZnO_n composites were found to be lower than that of the pure PZT with dielectric permittivity ε _r of 768–893, piezoelectric coefficient d ₃₃ of 240–260pC/N, mechanical quality factor Q _m of 340–650 and planar electromechanical coupling k _p of 0.5–0.55.