| Bismuth layer-structured lead-free piezoelectric ceramics have the widely studied owing to their high Curie temperature,high mechanical quality factor and low dielectric loss and other advantages.But the disadvatages is that bismuth layered ceramics have low piezoelectric property,which is difficult to be applied in life.In order to improve the piezoelectric properties of bismuth layered ceramics,researchers use ions with similar valence or radius for doping,or improve the preparation process by texture.According to the literature,doping modification mainly includes A,B,or A/B complex doping,as well as additive.In this work,Bi4Ti3O12(Tc?675oC)ceramic was selected as matrix materials,and the effect of A and B doped ions on the structure,microstructure and electrical properties of Bi4Ti3O12 ceramics was systemically investigated.The research contents of this dissertation mainly include the following three parts:Firstly,bismuth layer-structure piezoelectric ceramics of Bi4Ti3-x Wx O12(BITW,0.00?x?0.16)ceramics were synthesized by solid-state reaction method.The effect of W6+ modification on microstructure and electrical properties of the Bi4Ti3O12(BIT)ceramics was studied.It was found that the grains of the BIT ceramics were refined and the microstructure was homogenized at the optimal doping concentration of W6+.As a consequence,both the conductivity and dielectric loss of the ceramics were reduced,while the piezoelectric and electromechanical properties were enhanced,due to the improved densification of the materials.When the WO3 doping concentration was x=0.14,the ceramics exhibited optimum electrical properties with d33 = 16 p C/N,kp = 8.1%,Qm = 1942,?r = 160(at 100 k Hz),tan? = 1.6%(at 100 k Hz),TC = 632 oC and ? = 9.4 × 107?·cm at 500 oC,indicating that the BITW ceramics could have potential in high temperature applications.Secondly,based on the optimized composition of Bi4Ti2.86W0.14O12 ceramics,the sodium and cerium was introduced to the A-site of the crystal lattice,and the(Na0.5Ce0.5)x Bi4-x Ti2.86W0.14O12(abbreviated as NC100x-BITW,x=0?0.12)ceramics were prepared.The effect of(Na0.5Ce0.5)modification on microstructure and electrical properties of the Bi4Ti2.86W0.14O12 ceramics was studied.XRD results indicated that the NC100x-BITW ceramics possess a pure three-layer Aurivillius-type structure.(Na0.5Ce0.5)addition first increases and then decreases the grain size which can be observed by scanning electron microscopy.With the increase of(Na0.5Ce0.5)addition,the Curie temperature(Tc)was gradually decreased from 632 oC to 595 oC.The piezoelectric properties can be enhanced while the dielectric loss decreased after(Na0.5Ce0.5)addition,and the optimal properties were obtained as follows when x=0.06: d33=21.1 p C/N,kp=7.2%,Qm=4978,?r=147(@100 k Hz),tan?=0.27%(@100 k Hz),Tc=614oC and resistivity of 4.3×108?·cm at 500 oC.The improvement of piezoelectric constant and resistivity can expand the application of the material on high temperature sensing applications.Finally,based on the optimized composition of Bi4Ti2.86W0.14O12 ceramics,the potassium and cerium was introduced to the A-site of the crystal lattice of the ceramics,and the(K0.5Ce0.5)x Bi4-x Ti2.86W0.14O12(abbreviated as KC100x-BITW,x=0?0.1)ceramics were prepared.The effect of(K0.5Ce0.5)modification on microstructure and electrical properties of the Bi4Ti2.86W0.14O12 ceramics was studied.XRD results indicated that the KC100x-BITW ceramics possess a pure three-layer Aurivillius-type structure.An appropriate amout of(K,Ce)doped,the grain size becomes decreases and the dielectric loss decreases,the piezoelectric and electromechanical properties of ceramics are improved.The optimized properties were obtained as follows when x=0.08: d33=24 p C/N,kp=5.2%,tan?=0.28%(@100 k Hz),Qm=6766 and Tc=611oC.Moreover,the dielectric spectroscopy and thermal annealing studies indicated that the(K0.5Ce0.5)x Bi4-x Ti2.86W0.14O12 ceramic possesses stable piezoelectric and dielectric properties,indicating that the material is promising candidates on high temperature piezoelectric devices. |
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