Study On Modified Preparation And Properties Of New-type Potassium Sodium Niobate-based Lead-free Piezoelectric Ceramics

In the rapid development of information technology today, piezoelectric ceramics have become a hot research topic in the world due to their extensive and irreplaceable applications in electronics, optoelectronics, etc. a plurality of high-tech fields. And with the rapid development and special needs in the related fields, the piezoelectric ceramic is gradually developing towards lead-free, composite and nano-oriented, and so on. However, the application of piezoelectric ceramics is still dominated by PZT-based piezoelectric ceramics, which is a challenge to carry out the sustainable development of human beings and strengthen environmental protection. But after 2000, there was a qualitative change that use of traditional PZT lead based piezoelectric ceramics is proposed in the world, the use of traditional PZT-based piezoelectric ceramics has been put forward related ban in the world, and China has enforced the implementation of electronic information products pollution prevention and control measures in July 2006, and the study of lead-free piezoelectric ceramics included in the latest national strategic planning. For nearly 20 years of research, in the current research of several lead-free piezoelectric ceramics, potassium sodium niobate based piezoelectric ceramics have a good development potential, but it has been difficult to obtain dense ceramics by traditional sintering technology. This research of the paper is based on the research progress of KNN based lead-free piezoelectric ceramics at home and abroad and the previous research of our research group. On the one hand, the new system is put forward by ion substitution. On the other hand, the high properties, high density KNN-based lead free piezoelectric ceramics are obtained by adding composite sintering additives. The main research contents are as follows in this paper:1. By improving the sintering properties of KNN piezoelectric ceramics and its compactness, so as to obtain new high properties lead-free piezoelectric ceramics. In this research, we used the traditional ceramics processing technology, trace LiSbO3 as an additive was put forward for the first time at home and abroad, and SrTiO3 as a second component collectively modified KNN piezoelectric ceramics, the new KNN-ST-x lead-free piezoelectric ceramics were successfully prepared by using conventional ceramic preparation technology. XRD, SEM and other modern test analysis show that the KNN-ST-x (x=2-10% mol) ceramics have a high density and presents a single perovskite structure of tetragonal phase, which reveal a small amount of SrTiO3 and LiSbO3 composite modified, can effectively improve the density and electrical properties of KNN lead free piezoelectric ceramics. In particular, when x=0.04, KNN-ST piezoelectric ceramics doped with 6%mol LiSbO3 shows high density and excellent electrical properties, they are respectively d33=267pC/N, =46%, er-1168, tanδ=2.1%,P4=30.3μC/cm2, =1.98kV/mm.2. Envisaged through designing new phase boundary of KNN-based piezoelectric ceramics, in order to can enhance electrical properties of KNN-based piezoelectric ceramics. In this research, we first proposed that the KNN ceramics were collectively modified by B position substitution of Ni ions and the doping of second component SrTiO3. XRD, SEM and other modern test analysis show that the trace substitution of Ni ions not only did not appear any second impurity phase, but in the whole scope of the study can form a pure perovskite structure, and in the range of 0.02< x< 0.06, KNNN-ST-x ceramics exist a morphotropic phase boundary (MPB) between orthorhombic and tetragonal phases, and thus a high density and high properties of KNNN-ST piezoelectric ceramics were obtained when x=0.04, they are respectively *3=243pC/N, kp=47%, εr=1079, tanδ=2.3%, Pr= 26.4μ/cm2, =2.07kV/mm. This suggesting that the B position substitution of small amount of Ni ions and synchronous incorporation of SrTiO3, that can increase the density and the electrical properties of KNN piezoelectric ceramics and ensure the purity of the perovskite phase. At the same time, it is proved that establishing the new phase boundary is one of the effective methods to improve the KNN piezoelectric ceramics.3. Envisaged through B position substitution measures, so as to improve the sintering properties of KNN piezoelectric ceramics. In this research, we used the traditional ceramics preparation technology, the variable Sn ions and Sb ions at the same time to replace the Nb ions of B position for the first time was put forward, a new, high properties, high density of piezoelectric ceramic KNNSS were successfully prepared. XRD, SEM and other modern test analysis show that the KNNSS ceramics can form a pure perovskite structure of orthorhombic phase in the whole research range, and a moderate amount of Sn ions in the B position substitution, which can effectively enhance the liquid phase sintering, promote grain evenly growing, improve the density of ceramics, and effectively overcome the evaporation of K ion and Na ion in the high temperature. The results show that KNNSS piezoelectric ceramics presents an excellent electrical properties at x=0.03,they are respectively d33=288pC/N, kP=48%,ζr=1286, tanδ=2.9%,Pr=30.1μC/cm2, EC=1.01kV/mm, Tc=419℃. These results show that the moderate amount of oxygen vacancies result from the substitution of low valence ions for the Nb ions in the B position, that can improve the density and electrical properties of the KNN piezoelectric ceramics.4. Envisaged through the synchronous substitution measures in A position and B position, so as to obtain a new phase boundary of MPB. In this research, the effect of the the synchronous substitution in A and B positions with the second component LiTaO3 modification is obtained by using the traditional solid phase sintering technology. XRD, SEM and other modern test analysis show that a moderate amount of LiTaO3 substitution, that can obtain a single perovskite structure, and effectively promote the growth of the grain, increase the density of the ceramics, and greatly improve the piezoelectric properties of KNNSST ceramics. In particular, in the 0.025 < x< 0.045, piezoelectric ceramics KNNSST appeared a morphotropic phase boundary (MPB) of the orthorhombic-tetragonal phases coexist, and at x=0.035, piezoelectric ceramic KNNSST get excellent properties, they are respectively d33=348pC/N, kp=46%, εr=1316, tanδ=2.6%, Pr=25.8μC/cm2, =1.88kV/mm.5. Envisaged through adding sintering additives to achieve low temperature sintering preparation, in order to overcome the volatilization of sodium ions and potassium ions in the high-temperature preparation, so as to improve the density and electrical properties of KNN-based piezoelectric ceramics. This research uses traditional solid-state sintering technology, a high density, high properties lead-free piezoelectric ceramics KNNSC were successfully prepared with sintering additives CuO. XRD, SEM and other modern test analysis show that a moderate amount of CuO doped in the range of research can form a single perovskite structure, not found any second phase, and can promote grain evenly growing and improve the sintering properties of KNN-based piezoelectric ceramics.6. Envisaged through low temperature sintering technology to control the volatilization of sodium ions and potassium ions in the high-temperature preparation, in order to obtain the excellent physical properties of ceramics. In this research, we used the traditional ceramics preparation technology, KNN-based lead-free piezoelectric ceramics were prepared by using CuO and Na2O as the collective additives for the first time at home and abroad and under lower sintering temperature (1020℃) conditions. XRD, SEM and other modern test analysis show that the KNANTC ceramics can form a pure perovskite structure of tetragonal phase in the whole research range when 0.01mol Na2O as a supplement to the A position of KNN piezoelectric ceramics, and a moderate amount of CuO doping can enhance the liquid phase sintering, promote grain growing, improve the density of ceramics, and can obtain excellent electrical properties at the same time. The test results of KNANTC piezoelectric ceramics show a good electrical properties when x=0.035, they are respectively d33=343pC/N, kp=49%,εr=1382, tanδ=1.1%, Pr=24.9μC/cm2, =1.92kV/mm,Tc=306℃. These results indicate that KNANTC-x is a promising lead-free piezoelectric ceramics, which can gradually replace the traditional PZT based piezoelectric ceramics in the future.