Phase structures, PPT region and electrical properties of new lead-free KNLNTS-BCTZ ceramics fabricated via the solid-state combustion technique

(1−x)[(K0.44Na0.52Li0.04)(Nb0.84Ta0.10Sb0.06)O3]-x[(Ba0.85Ca0.15)(Ti0.90Zr0.10)O3]; (abbreviate to (1−x)KNLNTS-xBCTZ) lead-free piezoelectric ceramics were prepared via the solid state combustion technique and the effects of adding BCTZ compound (0≤x≤0.030 wt%) on the phase formation, morphology and electrical behavior of the compound ceramics were investigated. The X-ray diffraction (XRD) results at room temperature of all samples exhibited a single perovskite phase and the BCTZ efficiently diffused into the KNLNTS lattice during the sintering process to produce a solid solution. The crystal structure of these ceramics changed from O+T phases to higher T phase (0≤x≤0.020) and then began to change to a cubic phase when the x content increased from 0.025 to 0.030. A polymorphic phase transition (PPT) of (1−x)KNLNTS-xBCTZ ceramics was observed at an x content of 0.015 and the ratio of the orthorhombic and tetragonal phase was close to equal. Adding BCTZ compound at a ratio ≤ 0.015 promoted better morphology and higher densification. When the BCTZ compound was > 0.015, the microstructure and density of the samples deteriorated. The TO-T and TC of (1−x)KNLNTS-xBCTZ samples reduced continuously with increasing x content. Moreover, the (1−x)KNLNTS-xBCTZ showed a typical relaxor ferroelectric behavior with high BCTZ content. The optimum electrical properties, such as; the highest dielectric behavior (εr at Tr = 2194 and εm at TC = 6812), excellent ferroelectric properties (Pr = 27.9 µC/cm2 and EC= 9.9 kV/cm) and the highest d33 (295 pC/N) were obtained by the sample with x content of 0.015 wt%, this sample composition was confirmed to be in the PPT region. The addition BCTZ is a new alternative for improving densification, microstructure, ferroelectric and piezoelectric properties of KNLNTS ceramics.