Structures and properties of Gd3+ doped modified BiFeO3-BaTiO3 high-temperature lead-free piezoelectric ceramics

Abstract

Piezoelectric acceleration sensors are used for monitoring the vibration state of high-temperature components of some important technical equipment, such as aero engines and heavy gas turbines. These sensors require a high Curie temperature piezoelectric ceramic as a sensitive element, and "lead-free"electronic components are an urgent requirement for environmental protection. Gd/Mn co-doped high-temperature lead-free piezoelectric ceramics((0.67BiFeO3-0.33Ba1-xGdxTiO3)+0.5%(mass fraction)MnO2, x=0-0.02, BF-BT) were prepared by a traditional solid-state reaction process. The effects of doping concentration x of Gd3+ on the phase composition, microstructure, piezoelectric property, dielectric relaxation behavior and AC impedance characteristic of BF-BTceramics were investigated. The results show that all samples have pure perovskite structure with coexistence of tripartite phase (R) and tetragonal phase (T), and the T phase content increases with the increasing Gd3+ doping concentration. Moderate amount(x < 0.02)of Gd3+ dopant diffusing into the perovskite lattice would also promote the grain growth of BF-BT ceramics. Gd3+ doped samples exhibit enhanced relaxation phase transition behavior. The phase transition temperature (Tm) decreases with the increase of x, while the dielectric relaxation degree (ΔTrelax) increases with the increase of x. The R-CPE equivalent circuit model has been utilized to match the complex impedance spectra(Cole-Cole diagrams) of the BF-BTceramics, indicating that the AC impedance of samples at high temperature is mainly contributed by the grain boundary. The activation energy of dielectric relaxation increases with the increasing Gd3+ doping concentration, demonstrating the substitution of Gd3+ for Ba2+ can reduce the donor doping effect.In general, when x=0.01, the sample exhibits the optimized electrical properties, including TC=425 ℃, d33=126 pC/N, kp=25.9%, and tanδ=0.059. The Gd3+ doped BF-BTceramics are expected to be used as a promising high-temperature piezoelectric material.

Keywords

• bifeo3-batio3
• high-temperature lead-free piezoelectric ceramics
• ion doping
• dielectric relaxation
• ac impedance