| Bismuth layer-structured compounds, possessing unique structural features and high Curie temperature Tc, have been given more attention. The bismuth layer-structured lead-free piezoelectric ceramic materials have the wide application prospects in ferroelectric storage, high temperature and high frequency situations, filter, energy converter, and so on. However, the piezoelectric property of the ceramics is low because the rotation of the spontaneous polarization is restricted to the a-b planar plane. In this thesis, representative bismuth layer-structured piezoelectric materials of Na0.5Bi4.5Ti4O15(Tc?655?) ceramics were investigated, we engaged in the improvement of the piezoelectric activity in Na0.5Bi4.5Ti4O15 ceramics without producing a large decrease in their high TC. Good performance A or B (A/B)-site modified Na0.5Bi4.5Ti4O15 piezoelectric ceramic materials, with relatively high Tc(> 600??) and excellent electrical properties were obtained by using the traditional preparation and the conventional mixed oxide processing route procedure (at the pressure of< 18 MPa).Firstly, the Srx(Na0.5Bi0.5)1-xBi4TiO15 (SNBT-100x,0?x?0.200) bismuth layer-structured piezoelectric ceramics, the Sr replaced the A-site Na and Bi of the Na0.5Bi4.5Ti4O15(NBT) ceramics, were prepared by the solid state reaction method. It is found that the orthorhombic bismuth oxide layered structure of the ceramics can not change by the Sr modification. The electromechanical and electrical properties of NBT ceramics were improved by an appropriate amount of Sr addition. When x= 0.100, the ceramics achieves an optimum performance:the mechanical quality factor Qm=3519, piezoelectric constant d33=20 pC/N, planar electromechanical coupling coefficient kp=5.192%, thickness electromechanical coupling coefficient kt= 6.240%, dielectric permittivity ?r=162, dielectric loss tan ?= 0.657%, and Curie temperature Tc=626?. Moreover, the piezoelectric properties of the Sr modified-NBT(x= 0.100), which exhibits high piezoelectric stability, is improved.Secondly, the Na0.5Bi0.5-x(Nd,Ce)x/2Bi4Ti4O15 (NBT-x,0.0?x?0.4) bismuth layer-structured piezoelectric ceramics, which designed by using Nd and Ce co-replaced the A-site Bi of NBT ceramics, were prepared. It is found that all ceramics have an orthorhombic bismuth oxide layered structure. After an appropriate amount of (Nd,Ce) modification, the size of grain becomes small and the dielectric loss tan? reduces, meanwhile, the phase dispersion is observed, the piezoelectric and electromechanical properties of NBT-based ceramics are improved. When x=0.2, the ceramics achieves an optimum performance:d33=28 pC/N, Qm=3239, ?r=147,tan? =0.32%,Tc=630 ? kp=6.6%, and kt= 14.8%. Moreover, the researches on dielectric spectroscopy and thermal annealing studies indicated that the Na0.5Bi0.3(Nd,Ce)0.1Bi4Ti4O15 ceramic possesses stable piezoelectric and dielectric properties, demonstrating that the ceramic is the promising candidates for high-temperature piezoelectric devices applications.Finally, the Na0.5Bi4.5Ti4O15+x mol%Co2O3+y mol%MnCO3 (NBT-CM-x, y=0.1x, 0.0?x?7.0) ceramics, which designed by using CO2O3 and MnCO3 co-modified the NBT ceramics, were investigated. It is found that the ceramics with x?3.0 have a bismuth oxide layered structure. With the Co and Mn co-modification, the grain size of the ceramics increases. The Curie temperature (TC), higher than 635?, increases with the increasing amount of Co and Mn co-modification. The Cole-Cole plots show the presence of two semicircular arcs, suggesting the existence of grain and grain-boundary effects. The Variation of DC conductivity ?DC and the dielectric loss tan? are reduced, meanwhile, the comprehensive electrical properties are improved by a moderate amount of Co and Mn co-modification. When x=3.0, the ceramics achieves an optimum performance:d33=24 pC/N, Pr=11.70 ?C/cm2, Qm=3117, ?r= 198, tan?=0.19%, kp=9.9%, and kt=14.7%, which indicates that the ceramic has a good application potential. |
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