Ultrahigh strain in textured BCZT-based lead-free ceramics with CuO sintering agent

Abstract

• CuO as a sintering agent lowers the sintering temperature of 125 °C, and maintains BCZT-1.0 at a high texture degree of ∼99%. • CuO-based liquid phases eliminate boundaries between templates and matrix powders, release local stress, decrease grain sizes, and increase dielectric dispersion coefficient. • Maximum strain s max of 0.38% and low h s of 5.2% along with homogeneous d 33 ∼780 pC/N and large d 33 * ∼2950 pm/V was obtained in textured BCZT-1.0. Textured BaTiO 3 (BT)-based lead-free ceramics have gained significant attention due to their high piezoelectric coefficient ( d ) and very large field induced strain ( S ). However, costly nano-size raw materials, excessively high sintering temperature and low Curie temperature ( T c ) hinder their device applications. In this work, highly [001] c -oriented (Ba 0.95 Ca 0.05 )(Zr 0.04 Ti 0.96 )O 3 ceramics with x mol% CuO ( x = 0.25, 0.5, 1.0, 2.5) denoted as BCZT- x were synthesized by templated grain growth using micro-sized raw powders. The introduction of CuO sintering agent lowered the sintering temperature by 125 °C to 1450 °C, and the BCZT-1.0 achieved a high texture degree of ∼99%. In addition, the CuO-based liquid phases eliminated boundaries between BT templates and BCZT matrix powders. Such liquid-phase sintering reduced sintering stresses, decreased the average grain size of BCZT-1.0 from 16 μm down to 13 μm, and increased the dielectric dispersion coefficient γ to 1.63. The almost smoothed out T O-T anomaly in the temperature dependence of dielectric permittivity and comparably high T c (> 102 °C) lead to better temperature stability. The narrower grain orientation distribution with full width at half maximum (FWHM) of ∼5.9° and smaller domains with the size of 0.1–0.5 μm in width and 3–8 μm in length were obtained, a high field induced maximum strain S max of 0.38% and low H s of 5.2% have been achieved in BCZT-1.0 textured ceramics together with a high and homogeneous piezoelectric stress coefficient d 33 ∼780 pC/N and very large d 33 * ∼2950 pm/V.