【作者】 周佳骏；

【导师】 李敬锋；

【作者基本信息】 清华大学 ， 材料科学与工程， 2012， 博士

【摘要】 由于人们对环境问题的关注度越来越高，压电陶瓷的无铅化是未来发展的目标。铌酸钾钠（KNN）基无铅压电陶瓷被认为是最有可能替代传统的锆钛酸铅基陶瓷的材料之一，引起了人们广泛的研究。相结构对KNN基压电陶瓷的电学性能影响很大，本文从调控该陶瓷的相结构出发，致力提高其压电性能，获得了具有优异电学性能的KNN基无铅压电陶瓷。在一般条件下，发现了除组分和温度之外影响KNN基陶瓷的第3个因素，即应力状态对该陶瓷相结构的影响。在特定组分的该类陶瓷中，残余压应力会使得正交相更容易存在。当对块体样品进行退火处理之后，其相结构从处理前的两相共存转变为以四方相为主，这样使得其压电性能的温度稳定性得到提高。对于室温时两相共存的KNN基无铅压电陶瓷，我们分析了该陶瓷中复杂的相界，以及相结构和性能之间的关系。发现以Na/K=52/48为界，存在着两种不同的四方相和正交相。对应于这种准同型相界的四方相KNN陶瓷表现出高的压电性能；但是相比于四方相与正交相之间的多晶型相转变效应，这两种四方相之间的相转变对压电和铁电性能的影响较小。通过采用BiFeO₃和BiAlO₃来调控KNN基陶瓷的相结构，获得了具有良好温度稳定性的KNN基无铅压电陶瓷。BiFeO₃的加入可以使得该陶瓷发生相转变，而且有利于提高其烧结致密度和力学性能。在室温附近，我们获得了压电性能优异的KNN基陶瓷，d₃₃^*340pm/V， k_p⁴7.0%和Q_m⁷5。通过进一步精确控制陶瓷的相结构，可以获得压电性能的温度稳定性很好的KNN基陶瓷。当温度从室温上升到150oC时，该陶瓷压电常数d₃₃^*仅仅从303pm/V下降到264pm/V。适量BiAlO₃的加入既提高KNN基陶瓷的烧结致密度，又增强电学性能及其温度稳定性，d₃₃^*322pm/V，Pr¹5.9μC/cm2。使用AgSbO₃来精确调控组分优化后的KNN基陶瓷的相结构，获得了逆压电常数d₃₃^*高达598pm/V的KNN基陶瓷。为了将其应用到低温共烧的多层陶瓷驱动器中，我们分别添加LiF和CuO来实现该陶瓷的低温烧结。对于添加LiF的KNN基陶瓷，我们可以在低至900oC的烧结温度下获得d₃₃^*高达375pm/V的高密度块体。通过加入0.25wt%CuO，可以低至970oC的烧结温度下，获得d₃₃^*383pm/V，Q_m¹88和相对介电常数为860的KNN基无铅压电陶瓷。更多还原

【Abstract】 Lead-based piezoelectric ceramics such as Pb（Zr, Ti）O₃（PZT） have been widelyused for decades. Because of the toxicity of lead, lead-free piezoceramics have receivedincreasing attention from the view point of environment in recent years. Potassiumsodium niobate （KNN）-based ceramics are considered as one of the promising lead-freecandidates for its high piezoelectric properties. The electrical properties of KNN-basedpiezoceramics are strongly influenced by the phase structure. As one approach toimprove the piezoelectric property of KNN-based piezoceramics, modifying anddesigning its phase structure to gain high performance KNN-based piezoceramics.It is widely known that the composition and temperature greatly influence the phasestructure of KNN-based ceramics. Besides these two factors, we found that the internalstress could also influence its phase structure. For KNN-based ceramics with specificcomposition, the internal stress that existed in the ceramics favored the formation oforthorhombic phase. However, the phase structure would change from the coexistenceof orthorhombic and tetragonal to dominant tetragonal when the stress was released byannealing, which enhanced the thermal stability of piezoelectricity.We investigated the phase structure and electrical properties of KNN-basedpiezoceramics which show the coexistence of orthorhombic and tetragonal phases atroom temperature. When the Na/K ratio changed across52/48, it seemed that there wasa phase transition both for orthorhombic and tetragonal phases. The existence ofmorphotropic phase boundary in tetragonal KNN-based ceramics was verified, whichcould lead to the peak of electrical properties. However, when orthorhombic andtetragonal phases co-existed, the change of Na/K ratio made a little difference on thepiezoelectric and ferroelctric properties of the ceramics because of the predominantpolymorphism phase transition effect.BiFeO₃and BiAlO₃were used to modify the phase structure of KNN-basedpiezoceramics and KNN-based piezoceramics with good temperature-stablepiezoelectric property were obtained. The addition of BiFeO₃not only induced a seriesof phase transformations from orthorhombic to tetragonal and further to pseudocubic inKNN-based ceramics, but also enhanced its sintering densification behavior and mechanical strength. Enhanced room-temperature electrical properties of d₃₃^*340pm/V,k_p⁴7.0%and Q_m⁷5could be achieved in BiFeO₃-modified KNN-based piezoceramics.Furthermore, better piezoelectric properties with improved temperature stability couldalso be obtained in this ceramics, whose d₃₃^*changed a little from～303pm/V at roomtemperature to～264pm/V at150C. The addition of BiAlO₃into KNN-basedpiezoceramics showed a similar effect to that of the addition of BiFeO₃. Improvedelectrical properties of d₃₃^*322pm/V， Pr¹5.9μC/cm2could be obtained inBiAlO₃-modified KNN-based piezoceramics.AgSbO₃was doped into KNN-based lead-free piezoceramics with an optimizedcomposition to precisely control its phase structure and enhance its piezoelectricproperty. A large converse piezoelectric coefficient d₃₃^*up to598pm/V was obtained inthis kind of KNN-based piezoceramics. For the applications in lead-free multilayerpiezo-actuators, low-temperature sintering of KNN-based piezoceramics was developed.For LiF-doped KNN-based piezoceramics, dense sintered body with d₃₃^*375pm/Vcould be obtained at a low sintering temperature of900oC. The addition of0.25wt%CuO could also lead to the low temperature sintering of the ceramics. Electricalproperties of d₃₃^*383pm/V, Q_m¹88and εr⁸60were achieved in the CuO-dopedKNN-based piezoceramics sintered at970oC.更多还原