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

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 (Tc) higher than 260 °C. Thereby low-temperature (940 °C) sintering 0.09 Pb(Ni1/3Nb2/3)O3‒ 0.03 Pb(Mg1/2W1/2)O3‒0.88 Pb(Zr0.5Ti0.5)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, Tc = 303 °C) are achieved in the 0.70 wt% Ta2O5 added ceramic with a minimum activation energy of domain wall movement (Ea) 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 Ea, the smaller the domain, and the higher the piezoelectric response. Low Ea 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 Ea and the domain structure reveals the origin of the high piezoelectricity in the low-temperature sintering PZT-based relaxor ferroelectric ceramics.