Origin of high piezoelectricity in low-temperature sintering PZT-based relaxor ferroelectric ceramics

Highlights: • 940 °C sintering PZT have high piezoelectricity: d₃₃ = 640 pC/N, T_c = 303 °C. • The larger the CTP, the lower the E_a. • The larger the CTP, the higher the piezoelectric response. • The lower the E_a, the smaller the domain size. • The smaller the domain size, the higher the piezoelectric response. -- Abstract: Multilayer piezoelectric devices need to co-sinter the piezoelectric ceramic layers and the Ag-rich Ag–Pd internal electrode layers at a low temperature (less than the Ag melting point of 961.78 °C), and need to use Sn–Zn-based lead-free solder to weld the components at 260 °C. This requires low-temperature sintering of high-performance piezoelectric ceramics with a Curie temperature (T_c) higher than 260 °C. Thereby low-temperature (940 °C) sintering 0.09 Pb(Ni_1/3Nb_2/3)O₃‒ 0.03 Pb(Mg_1/2W_1/2)O₃‒0.88 Pb(Zr_0.5Ti_0.5)O₃ ceramics are prepared via the solid-state reaction method. Samples added with different Ta₂O₅ contents are fabricated and compared in terms of phase structure, microstructure, piezo-/ferro-electric properties, and dielectric relaxation. High piezoelectric properties (d₃₃ = 640 pC/N, d₃₃∗ = 676 p.m./V, T_c = 303 °C) are achieved in the 0.70 wt% Ta₂O₅ added ceramic with a minimum activation energy of domain wall movement (E_a) of 0.025 eV. Rietveld refinement and Raman spectroscopy show that all the ceramics exhibit rhombohedral-tetragonal (R-T) coexistence and the distortion degree of crystal structures increases with the increase of Ta₂O₅ content. Our results show that the larger the content of the tetragonal phase (CTP), the lower the E_a, the smaller the domain, and the higher the piezoelectric response. Low E_a favors orientation and extension of polar regions and facilitates the formation of the nanometer-size domain structure (polar nanoregions) which is observed by using piezoresponse force microscopy, thus resulting in high piezoelectric properties. This mechanism associated with the CTP, the E_a and the domain structure reveals the origin of the high piezoelectricity in the low-temperature sintering PZT-based relaxor ferroelectric ceramics.