Temperature stable and fatigue resistant lead-free ceramics for actuators

Abstract

Lead-free ceramics with the composition 0.91K1/2Bi1/2TiO3–0.09(0.82BiFeO3-0.15NdFeO3-0.03Nd2/3TiO3) were prepared using a conventional solid state, mixed oxide route. The ceramics exhibited a high strain of 0.16% at 6 kV mm−1, stable from room temperature to 175 °C, with a variation of <10%. The materials were fabricated into multilayer structures by co-firing with Pt internal electrodes. The prototype multilayer actuator exhibited constant strains up to 300 °C with a variation of ∼15%. The composition showed fatigue resistant behaviour in both monolithic and multilayer form after bipolar loading of 106 cycles.

Designing pseudocubic perovskites with enhanced nanoscale polarization

“…As reported previously [8], the 91KBT-09BNFT composition exhibits dielectric relaxation and slim P-E loops consistent with those of relaxor ferroelectrics. This material generates high, temperature-stable electromechanical strain (S), which makes it of interest for practical applications.…”

“…The archetype system of this type is lead zirconium titanate [1], the properties in which are amplified at the rhombohedral-tetragonal morphotropic phase boundary (MPB). For decades, the search for commercially viable formulations has focused on such MPB compositions but, recently, a different class of perovskite oxides has emerged that also exhibits technologically attractive functional properties [e.g., [2][3][4][5][6][7][8][9][10][11]. These materials are multicomponent metal components) solid solutions of distorted end-members but which by powder diffraction appear to have the cubic (pseudocubic) symmetry of an ideal ABO3 perovskite structure (space group Pm3m, lattice parameter a Å .…”

“…In some of the known pseudocubic perovskite solid solutions, the distortions are coherent over a scale of only a few nanometers (or less), whereas in others their coherence extends over a longer range but remains weak and, therefore, unresolvable even with high-resolution diffractometers. Examples of the first type of structures can be found in BaTiO3-BiMO3 (M=Sc, Mg½Ti½, Zn½Ti½) systems [11], which yield dielectric properties of interest for high-energy capacitor applications; and in Bi½K½TiO3-(Bi,Nd)FeO3 ceramics that generate strong, temperature-stable electromechanical responses [8]. An example of the second type is (K,Bi)(Nb,Fe)O3, which displays a widely tunable band gap in a long-range but weakly correlated ferroelectric structure [9].…”

“…The Fe 3+ (R=0.645 Å) ions are non-ferroelectric but support large lattice distortions in the tetragonal PbTiO3-BiFeO3 phase [21,22], and, thus, may not necessarily act species. While the pseudocubic phase in KBT-BNFT has been reported previously [8], we included it here for consistency and a more detailed characterization of its structure.…”

High strain (0.4%) Bi(Mg2/3Nb1/3)O3‐BaTiO3‐BiFeO3 lead‐free piezoelectric ceramics and multilayers

“…Comparison of the variation with PZT and other PbO free materials is given in Table . These results suggest that BBTF may have the potential to operate at higher temperatures than typical for PbO‐free ceramics which often have low depolarising temperatures or a decrease in piezoactivity as temperature increases …”