【作者】 冯斌；

【导师】 肖定全；

【作者基本信息】 四川大学 ， 材料物理与化学， 2007， 硕士

【摘要】 采用传统固相烧结工艺制备了xLiNbO₃-（1-x）Na_0.5K_0.5NbO₃（简写为LNKN，其中0.146≤x≤0.618）高温无铅压电陶瓷。讨论了烧结温度、极化条件对陶瓷材料的影响；运用X射线衍射分析和扫描电子显微镜技术对制备出的陶瓷材料的相结构、微观组织等进行了分析，研究了陶瓷材料的晶相结构随x含量的变化并提出变化模型；讨论了LNKN高温无铅压电陶瓷的介电、压电性能随x的含量的变化趋势。结果表明，LNKN无铅压电陶瓷是高温无铅领域中很具有前景的一类材料。通过实验研究，我们发现：1．高Li含量的LNKN随着x的增加，发生了一个从四方钙钛矿相到四方钨青铜相、再到LiNbO₃相的转变，结构的变化也正是由于Li的加入引起晶格的畸变而形成的。2．在NKN的钙钛矿相和LiNbO₃相之间存在着一个过渡相，即K₃Li₂Nb₅O₁₅或K₃LiNb₆O₁₇的四方钨青铜相。其中K₃Li₂Nb₅O₁₅是一种完全填满型钨青铜结构，而K₃LiNb₆O₁₇是一种非填满型钨青铜结构，尚存在着碱金属阳离子的空位。3．在LiNbO₃的含量一定时，陶瓷中可能存在四方钙钛矿相、四方钨青铜相以及三方LiNbO₃相中的多种，形成复相结构。4．与准同型相界（MPB）类似，钙钛矿相与钨青铜相的转变以及钨青铜相与LiNbO₃结构的转变是一个突变的过程。即可以同时存在其中一种或几种相，但是几乎不明显存在它们之间的某种混乱的杂相。5．NaNbO₃与KNbO₃是无限固溶体，但是NaNbO₃和KNbO₃，与LiNbO₃并不是无限固溶体。当LiNbO₃的含量较低时，可以与NaNbO₃、KNbO₃固溶而形成钨青铜结构，但当含量较高时，首先会有NaNbO₃析出，然后KNbO₃也会因晶格的畸变而析出。6．当x在0.25到0.45之间时，d₃₃几乎保持不变，大约为70～80pC／N。当x=0.382时，压电常数d₃₃=74pC／N，居里温度T_c=526℃。当x=0.500时，压电常数d₃₃=53pC／N，居里温度T_c=537℃。7．当加入助熔剂CuO时，机械品质因子Qm从52提高到82，而且并没有引起居里温度的剧烈下降，但是压电常数却下降很多。通过本论文的研究，取得以下具有明显创新性的研究成果：1．提出了高LiNbO₃含量LNKN无铅压电陶瓷（其中0.146≤x≤0.618），并成功制备并表征了居里温度大于500℃，压电常数在70到80pC／N的高温无铅压电陶瓷。2．对高锂含量LNKN系列陶瓷进行了相结构和微观组织进行了表征，首次提出高锂含量LNKN陶瓷随Li含量的相结构的变化。更多还原

【Abstract】 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.更多还原