| Because lead zirconate titanate (PZT) and PZT-based piezoelectric ceramics possess excellent electrical and piezoelectric properties, they have been widely used in various applications. But as is well-known to all, the lead element is harmful to environment and human health, so it is necessary and urgent to develop lead-free ceramics with excellent piezoelectric properties to replace lead-containing ceramics. The alkalis niobate piezoelectric ceramics is thought to be one of the candidates of the alternative lead-containing ceramics system. In this work, it mainly discusses three new piezoelectric ceramics (K0.94-xNaxLi0.06)(Nb0.94Sb0.06)03(KNL NS-x),(K0.44Na0.5Li0.06)(Nb0.94-xTaxSb0.06)03(KNLNTS-x) and (1-x)NaNbO3-xBi0.5Li0.5TiO3(NN-BLT-x), they have been fabricated by conventional ceramics sintering technique, their structure, piezoelectric, dielectric and ferroelectric properties were studied in detail. The main conclusions from the present work are as follows:(1) New lead-free piezoelectric ceramics (TK0.94-xNaxLi0.06)(Nb0.94Sb0.06)03(KNL NS-x) are invented and have been fabricated by conventional ceramics sintering technique, effects of the ratio of Na/K on the ceramics were studied. The results of X-ray diffraction shows that all the ceramics can be well sintered and exhibit a dense, a single pure perovskite structure. In the crystal structure, the crystal phase of the ceramics gradually transformed from the orthorhombic transition to the tetragonal phase, and orthorhombic phase and tetragonal phase coexist in the KNLNS-x ceramics with0.35<x<0.55at room temperature. When x (the content of Na+) increases in the ceramic system, the sintering temperature gradually increases. All the KNLNS-x ceramics possess excellent ferroelectric properties. The result also shows the optimum poling condition is poling field E=4kV/mm, poling temperature T=20℃and poling time t=30min. Under the optimum technique, the ceramics with x=0.5exhibits the excellent piezoelectric and dielectric properties:d33=233pC/N, kp=49%, εr=1172, Tc=362℃and Pr=24μC/cm2.(2) Based on KNLNS-0.5ceramics, new lead-free piezoelectric ceramics (K0.44Na0.5Li0.06)(Nb0.94-xTaxSb0.06)O3(KNLNTS-x) were invented and prepared. All the KNLNTS-x ceramics can form a solid solution with a pure tetragonal perovskite structure, and the tetragonality decreases at high Ta5+doping level. When the content of Ta5+increases, the sintering temperature gradually increases, at the same time To-T and Tc gradually reduce. It suggests that when the concentration of Ta5+is lower, the properties can be improved, for the ceramic with x=0.05exhibits the excellent piezoelectric and dielectric properties:d33=248pC/N, kp=50%, εr=1634and Tc=330℃, it also possess good ferroelectric properties (Pr=22μC/cm2). The KNLNTS-0.05ceramic also exits very good temperature stability of piezoelectric properties. But when the concentration of Ta5+is higher, the piezoelectric, dielectric and ferroelectric properties decrease obviously.The (K0.44Na0.5Li0.06)(Nb0.89Ta0.05Sb0.06)O3+xwt%Ga2O3ceramics (KNLNTS-G a-x) were invented and fabricated, effects of the content of Ga2O3on the structure and properties for KNLNTS-0.05were studied. The results of X-ray diffraction analysis show that all the ceramics can be well-sintered and exhibit a dense microstructure and pure perovskite phase. All the ceramics possess good ferroelectric properties at0≤x≤2. After the addition of Ga2O3, the grains of the ceramics become smaller and Curie temperature Tc of the ceramics gradually increases. The ceramics exhibit poor piezoelectric properties. (3) New lead-free piezoelectric ceramics (1-x)NaNbO3-xBi0.5Li0.5TiO3(NN-BLT-x) have been prepared, the properties have been studied in detail. The Bi0.5Li0.5TiO3diffuses into NaNbO3lattices to form a peroskite solid solution with an orthorhombic symmetry at0.025≤x≤0.175, and the orthorhombicity decreases at high Bi0.5Li0.5TiO3doping level. The ferroelectricity of the ceramics is induced after the addition of Bio.5Lio.5TiO (x=0.025). It suggests that when the concentration of Bi0,5Li0.5Ti03is lower, the properties can be improved significantly, for the ceramics with x=0.075are normal ferroelectric and then the ferroelectric-paraelectric phase become diffusive with increasing x. The NN-BLT-0.075ceramic exhibits the relatively large piezoelectric constant (d33=59pC/N and kp=18%), high Curie temperature (Tc=228℃), good temperature stability and high Pr. When the content of Bi0.5Lio.5Ti03increases, Tc gradually reduces.The0.925NaNb03-0.075(Bi0.5Li0.5)TiO3+xmol%MnO2ceramics (NN-BLT-Mn-x) were invented, effects of the content of MnO2on the NN-BLT-0.075ceramics were studied. The results of X-ray analysis show that MnO2diffuses into NN-BLT-0.075lattices to form a peroskite solid solution at0≤x≤2. The effect of addition MnO2on the structure and piezoelectric of the NN-BLT-0.075ceramics is not significant. |
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