Phase transition,electrical properties and large strain response in lead-free (1-x-y)BNT-xBKT-yKNN ceramics

Abstract

Lead-free piezoelectric composition ceramics of (1-x-y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃–yK_0.5Na_0.5NbO₃; (1-x-y)BNT-xBKT-yKNN (with 0.18≤x?≤?0.26 and 0≤y?≤?0.07) were fabricated using the solid-state combustion method. The structure exhibited co-existing rhombohedral and tetragonal phases for all samples. Increasing of x and y contents, the average grain size decreased from 1.42?μm to 1.02?μm and 1.25?μm to 0.70?μm, respectively. The diffuseness exponent (γ) of the ceramics was between 1.817 and 1.939 for x composition and between 1.766 and 1.999 for y composition indicating that the (1-x-y)BNT-xBKT-yKNN solid solutions had diffuse phase transition behavior. The change in the P-E loops of the ceramics indicated that the long-range ferroelectric order of the samples was disturbed and turned to the polar nano-regions (PNRs) with increased x and y contents. The polarization hysteresis loop transformed from well saturated typical ferroelectric, to pinched, and then to the relaxor state with increased x and y content. The addition of BKT and KNN contents significantly enhances the field-induced strain in BNT ceramics. The largest S_max of 0.25% corresponded to a high-field effective d₃₃* of 509?pm/V, which was found in the composition of 0.79BNT-0.20BKT-0.01KNN.     

Phase Formation,Dielectric, Ferroelectric and Magnetic Properties of Cr2O3 Doped (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 Ceramics

Abstract

In this paper, we studied the effect of Cr₂O₃ doping (0–0.8?wt%) on the phase formation, dielectric, ferroelectric and magnetic properties of (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ (BCTZ) ceramics prepared by the solid state combustion method. All samples were prepared with a calcined and sintered temperature of 1050?°C and 1450?°C, respectively, for 2?h. The results of the XRD patterns showed the coexistence between the tetragonal (T) and orthorhombic (O) phases for all samples, and the tetragonal phase increased with increasing amounts of Cr₂O₃. The dielectric constant decreased when Cr₂O₃ increased. The P-E hysteresis loops of the BCTZ ceramics doped with Cr₂O₃ between 0 and 0.2?wt% showed slim and saturated loops. By increasing Cr₂O₃ doping from 0.4 to 0.8?wt%, the P-E loops were unsaturated and a leakage current was produced. The undoped BCTZ ceramics exhibited diamagnetic behavior. The sample with 0.2?wt% Cr₂O₃ showed ferromagnetic behavior. Increasing Cr₂O₃ doping from 0.4 to 0.8?wt%, caused the ceramics to exhibit paramagnetic behavior. Doping with Cr₂O₃ led to improper ratios between the tetragonal and orthorhombic phases, decreased density and increased porosity which caused a decrease in the electric properties.     

Phase formation and electrical properties of Ba(ZrxTi1−x)O3 ceramics synthesized through a novel combustion technique

High quality Ba(Zr_xTi_1?x)O₃ (BZT, 0.025≤x≤0.150, step=0.025) ceramic has been prepared by the combustion technique. The raw materials were mixed with CH₄N₂O and calcined at 1000 °C and sintered at 1375 °C. For Ba(Zr_xTi_1?x)O₃ with x=0.025, the ceramics exhibited orthorhombic structure at room temperature. The crystal structure was transformed to rhombohedral, tetragonal and cubic phase, respectively with increasing zirconium content. The effect of x on dielectric properties has been studied intensively. It is found that the phase formation, which was affected from zirconium substitution, strongly influences the dielectric behavior. The rhombohedral phase decreases the maximum dielectric constant while the tetragonal phase enhances it. An extrapolation studied revealed the phase transition peaks merged into one peak at x ～0.094. The highest diffuseness constant of 1.95 was observed in BZT with 0.075 mol% zirconium. This was caused by the broadest dielectric peak of ferroelectric phase transition and the imminent diffusion between ferroelectric phase transition peak and Curie phase transition peak. The ferroelectric properties were sensitive to the phase exhibited in BZT system.