| In this dissertation, the n(K)/n(Na) compositional ratio issue was examined. The n(K)/n(Na ratio influence on the microstructures, phase transitions, dielectric and piezoelectric properties in KxNa1-xNbO3 lead-free piezoelectric ceramics was investigated in the compositional range of x=0.44~0.51. The experimental results showed that K0.49Na0.51NbO3 (abbreviated as NKN) ceramics with the composition of n(K)/n(Na deviated from the 1:1 ratio has better piezoelectric properties. Furthermore, the different content of LiNbO3,LiSbO3 and LiTaO3 modified on the microstructures structures, phase transitions, dielectric and piezoelectric properties in NKN-based piezoelectric ceramic were investigated.The n(K) /n(Na) ratio influence on the electrical properties in KxNa1-xNbO3 was investigated in the compositional range of x=0.44~0.51. The experimental results showed that all samples show a pure perovskite structure phase with typical orthorhombic structure. The existence of a change in the line slopes of lattice parameter variation with x is disclosed in the vicinity of x=0.49. The lattice parameter discontinuity at x=0.49 was found in the compositional range. This lattice parameter discontinuous change can be considered two orthorhombic structure coexistence that morphtropic phase boundary (MPB). Because of such MPB behavior,the ceramic sample exhibits optimal piezoelectric properties: d33=146pC/N,Qm=157,εr=406,tanδ=0.036,Tc=403,kp=43%.Effects of LiNbO3 (LN)-doping on the microstructures, phase transitions, dielectric and piezoelectric properties of (1-x)K0.49Na0.51NbO3-xLiNbO3 (NKNLN) were studied. The results present that the system still has pervoskite structure which means LN-doping has not effects on crystal structure, but the second phase, tungsten bronze structure phase appears in Li-doped NKN-based materials. The x-ray diffraction patterns shows that a morphotropic phase boundary between orthorhombic and tetragonal ferroelectric phases has been identified in the composition range of 0.05 |
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