Stabilization of the morphotropic phase boundary in (1−x)BNT-xBCTS ceramics prepared by the solid-state combustion technique

Abstract Producing lead-free Bi0.5Na0.5TiO3 (BNT)-based ceramics with a composition near the morphotropic phase boundary (MPB) region is highly important to optimize the piezoelectric properties. Therefore, a range of the ceramic compositions, designed to be near the MPB region were attempted and investigated to confirm the phase was at MPB for the lead-free BNT-based ceramics, which is needed to improve the piezoelectric performance. The aim of this work is to study the design of (1-x)Bi0.5Na0.5TiO3-x(Ba0.945Ca0.055)(Ti0.91Sn0.09)O3 ((1-x)BNT-xBCTS)) ceramics by forming ceramics with compositions around the MPB region (x = 0.03–0.09), synthesized via the solid-state combustion technique using glycine as the fuel. The influence of the x content on phase formation, local structure, microstructure, and electrical properties of (1-x)BNT-xBCTS ceramics was investigated. The X-ray diffraction (XRD) patterns exhibited coexisting phases between the rhombohedral (R) and tetragonal (T) phases in all compositions and the T phase increased with increasing x content. Rietveld analysis of the XRD data and the X-ray absorption spectroscopy (XAS) with the EXAFS technique confirmed the stable formation of a coexisting R + T perovskite phase for all ceramics and the ratio of R:T phases was obtained for both techniques with nearly identical values. The ceramic with x = 0.07 exhibited a MPB region with a coexisting R + T perovskite phase at room temperature (with ratio of R and T phases close to 50:50), this composition showed the highest density and the highest electrical parameters (er ≅ 1998, em ≅ 6995, Pr ≅ 32.67 μC/cm2, Ec ≅ 17.54 kV/cm, Smax ≅ 0.199% d 33 ∗ ≅ 308 pm/V and d33 ≅ 202 pC/N). These findings make the (1-x)BNT–xBCTS lead-free ceramics produced with a composition near the MPB zone are very promising as candidates for lead free piezoelectric materials.