Research On Preparation And Properties Of XLiNbO₃-(1-x)(K_0.5Na_0.5)NbO₃(LNKN) High-temperature Lead-free Piezoelectric Ceramics With High Content Of Lithium

xLiNbO₃-(1-x)Na_0.5K_0.5NbO₃ (abbreviated as LNKN) which x was selected between 0.146 and 0.618 were fabricated by Conventional Solid-state Sintering method. The effects of sintering temperature and polarization conditions on the properties of ceramics were discussed. The crystal structure, surface appearance, dielectric and piezoelectric properties were studied with the increase of x in this paper.Through this work, the main novel conclusions obtained are as follows:1. With the increase of Li, the crystal structures of LNKN ceramics have a transformation process from tetragonal perovskite phase to tetragonal tungsten bronze phase and then to a rhombohedral phase of LiNbO₃ type by the distortion of crystal lattice.2. There are such transition phases as K₃Li₂Nb₅O₁₅ and K₃LiNb₆O₁₇ tungsten bronze structures between the phases of NKN and LN.3. When x is a certain value, there are one or more phases of tetragonal perovskite phase, tetragonal tungsten bronze phase and LiNbO₃ phase. They form a multi-phases crystal structure.4. Analogous to MPB, the transformation between these phases is an abrupt process. There could be one or more phases of the three ones mentioned above.5. NaNbO₃ and KNbO₃ are infinite solid solution but they are not infinitely dissolved with LiNbO₃. When x is more than a certain value, NaNbO₃ separates from the solid solution and then KNbO₃ separates with the continuous increase ofx.6. When x increases, the piezoelectric constant declined but it holds in a range of 70～80pC/N stably between 0.236 and 0.438 of x. When x=0.382, Piezoelectric constant d₃₃=74pC/N and Curie Temperature T_c=526℃. Whenx=0.500, d33=53pC/N and Tc=537℃。7. If fusing agent CuO is added into the ceramics, the quality factor will be promoted significantly with small decline of Curie temperature, however, the piezoelectric properties decreases.Through this work, some innovative achievements are described as below:1. Lead-free piezoelectric ceramics used in high temperature environment with LNKN system(0.146≤x≤0.618) were put forward and fabricated, which have high piezoelectric constant between 70 and 80 pC/N and high Curie temperature above 500℃.2. Crystal phases and micro structure of high lithium LNKN based ceramics were carefully characterized. The lattice transformation of LNKN based ceramics with the increase of x were first carried out.