| Recently, great attentions have been paid to BiScO3-PbTiO3and BaTiO3-based perovskite-type ferroelectric solid solutions for their excellent properties and special structure in the compositions near Morphotropic Phase Boundary (MPB). The ternary ceramic systems related to the two materials have been studied extensively. Generally, it is an effective mean for searching new piezoelectric materials according to the known material and to control of the composition and structure of the material. If a guiding rule or parameters of performance and characteristics can be obtained to excute preliminary theoretical judgment, the MPB would be determined to guide experimental design. In addition, it will be instructive to reduce the experimental cost and to eliminate blind development in the course of studying performance and mechanism. In this paper, the phase transition behavior, dielectric, ferroelectric, piezoelectric, electric field-induced strain and their microscopic mechanism are studied in order to improve electrical properties for the Pb(Ni1/3Nb2/3)O3-BiScO3-PbTiO3(PNN-BS-PT) and BaTiO3-CaTiOs-BaHfO3(BT-CT-BH/BCHT) piezoelectric ceramics.The BS-PT system ceramics at MPB possess good piezoelectric property and a high Curie temperature as a kind of excellent piezoelectric material. For the new ternary PNN-BS-PT system, the compositions in xPNN-(1-x)(0.30BS-0.70PT) ceramics were selected in its ternary phase diagram, which close to the line connecting two MPB compositions, i.e. BS-0.64PT and PNN-0.36PT, respectively. Compositions with enhanced electrical properties can be conveniently exploited in the ternary system as its generality. The relationship of composition-structure-properties is investigated to identify the MPB with coexisting R-T phases, which is located at approximately x=0.34-0.36. The optimum composition shows enhanced properties with piezoelectric coefficient d33=490pC/N, electromechanical coupling factor kp=44%, and electric field-induced strain Smax (%)=0.30%. With increasing PNN content, it is found to decerase the Curie temperature TC and increase the d33and Smax (%) with comparing the MPB composition in BS-PT ceramics. On the other hand, the ceramics in the ternary system have a wider range of sintering temperature.Firstly,0.52Ba(Hf0.16Ti0.84)O3-0.48(Ba0.70Ca0.30)TiO3(abbreviated as BH0.16T-0.48BC0.30T) ceramics were prepared by a conventional solid-state reaction method based on BH-BT and BT-CT systems. The effect of sinering temperature on the microstructure and electrical properties were investigated. Lead-free BCHT-xCu piezoelectric ceramics have been fabricated by a solid-state reaction process using CuO as the sinering aid, which results in a reduction of sintering temperature from1480℃to1350℃. The excellent piezoelectric property was achieved for the CuO-doped BCHT ceramics, which d33and kp of BCHT-xCuO ceramics increases from372to461pC/N,48.8%to53.7%(higher than50%of PZT-8) respectively, with the increase of CuO content from0to0.50mol%.Microstructure, phase structure, and electrical properties are studied for BH0.16T0.84-xB0.7C0.30T ceramics, including its phase transition behavior and characteristics. The results indicate the change of phase structural in ceramics from R phase to O phase and then to the zone of O-T coexistence (x=0.48). The BCHT system showed the existence of three types of dielectric behavors in the BT-rich region based on the dielectric behaviors. The enhanced piezoelectric property is confirmed to be related to the O-T coexisting intrinsic properties. Meanwhile, the (Ba0.90Ca0.10)(HfxTi1-x)O3ceramics were fabricated to analyze their dielectric relaxor behaviors based on empirical parameters (△Tm,and△Trelax, respectively).In this study, we designed three composition groups with a head-to-tail arrangement, i.e. BH0.16T-xBC0.20T, BH0.16T-xBC0.30T, BH0.20T-xBC0.30T in the BCHT system for the transition complexity of BaTiO3-CaTiO3-BaB’O3(B’=Zr, Hf, Sn), to understand the variation of the intermediate O-phase region and its effect on the electrical properties. The composition-temperature phase diagrams in three composition groups have been proposed based on the X-ray diffraction patterns and the temperature-dependent dielectric behaviors. The O-phase zone exists in every phase diagram in spite of its small O-phase volume occupancy. The high dielectric and piezoelectric properties are believed to originate from O-T coexistence, which the possible physical mechanisms are analyzed according to the evolution of phases. The linear rule of the compositions with O-T phase boundary has been presented in the ternary system. In addition, a quantitative relation between the phase boundary composition and atomic mole ratio of Hf to Ca (Rm) is proposed, which the Rm value corresponding to the phase boundary is about0.58. This simple but powerful rule is further supported by other similar system, providing new clues for designing BT-based piezoelectric materials with enhanced piezoelectric property. |
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