【作者】 潘劲松；

【导师】 张孝文；

【作者基本信息】 清华大学 ， 材料科学与工程， 2006， 博士

【摘要】 组成在准同型相界附近的钙钛矿型铁电固溶体由于在结构和性能方面的特殊性而备受人们的关注,本论文从提高电学性能的角度出发对这类材料进行了系统的研究。本文归纳并提出了三元陶瓷体系中准同型相界组成的线性组合规律,并通过设计的实验进一步验证了此规律的普遍适用性。线性组合规律可以成为三元系统中寻找具有较好性能组成的指导原则。依照线性组合规律选择了PNN–PZN–PT体系中的系列组成,采用铌铁矿预产物法合成了具有这些组成的陶瓷,并对其相结构和性能进行了研究。结果表明,此三元系统中存在较宽的线性准同型相界区,富Zn的组成区域含有焦绿石相,性能较好的组成集中在富Ni区,其中0.56PNN–0.14PZN–0.30PT陶瓷的极值介电常数为约24500,压电系数达到730pC/N左右。在PMN–PNN–PT的三元陶瓷体系中同样也发现了线性的准同型相界区,此系统中较理想性能的组成为0.53PMN–0.13PNN–0.34PT,其极值介电常数和压电系数分别达到32000和700pC/N左右。将线性组合规律进一步运用到四元体系中。由PNN–PZN–PT和PMN–PNN– PT中性能较好的组成点经过线性组合得到的PMN–PNN–PZN–PT四元系陶瓷显示出了更为优异的电学性能,其中部分试样的极值介电常数达到36000? 37000,压电系数达到860? 900pC/N左右。这表明,组元的多样化是提高陶瓷电学性能的有效途径,而线性组合规律在更多组元构成的体系中也是适用的。比较了不同气氛条件下烧成的同组成PMN–PNN–PT陶瓷的电学性能,发现高温条件下铅含量的挥发将会导致铅基钙钛矿型铁电陶瓷性能的下降。通过实验观察到了铅基钙钛矿型铁电陶瓷中具有自由生长形貌的晶粒,在此基础上提出了铅基弛豫铁电单晶的生长机理。这不仅有助于我们解释实验中观察到的一些现象,也能够阐明文献中报道的一些弛豫铁电单晶的外观形貌形成的原因,并可为单晶生长工艺的进一步改进提供依据。更多还原

【Abstract】 Perovskite-type ferroelectric solid solutions near the morphotropic phase boundary (MPB) have attracted much attention owing to their special structure and properties. This dissertation mainly focuses on such ferroelectric systems aiming at the improvement of their electrical properties.The linear combination rule of compositions near the MPB in ternary ceramic systems has been presented, and its generality was further proved through a series of designed experiments. According to this rule, compositions with super electrical properties can be conveniently exploited in ternary systems.A series of compositions in the PNN–PZN–PT system were selected according to the linear combination rule. Ceramics with such compositions were fabricated using the columbite precursor method, and their phase structure and properties were investigated in detail. The results demonstrated that there is a wide linear MPB region in such ternary system. Since ceramics with compositions in the Zn-rich region have partial contents of pyrochlore phases, compositions with better properties are in the Ni-rich region. Ceramics with the composition of 0.56PNN–0.14PZN–0.30PT has high peak dielectric constant (24500) and piezoelectric coefficient (730pC/N). In the same way the wide linear MPB region was also demonstrated in the PMN–PNN–PT system. The peak dielectric constant and the piezoelectric coefficient of the 0.53PMN–0.13PNN–0.34PT ceramics reach 32000 and 700pC/N, respectively.The linear combination rule was further applied in the quaternary system. A series of PMN–PNN–PZN–PT compositions were obtained through the linear combination of ternary compositions with super properties in PNN–PZN–PT and PMN–PNN–PT systems. The results demonstrated that the selected quaternary compositions exhibit superior electrical properties than those in ternary systems. The peak dielectric constant and the piezoelectric coefficient of some quaternary compositions reach as high as 36000 ? 37000 and 860 ? 900pC/N, respectively, indicating that the introduction of more components in the ferroelectric system mayhelp to improve the electrical properties of materials, and the linear combination rule is also applicable for multiple-component systems.Electrical properties of the PMN–PNN–PT ceramics sintered in different atmosphere were compared. It was found that the loss of lead at high temperature severely degraded the properties.The growth mechanism of lead-based relaxor ferroelectric single crystals were proposed based on the observation of the morphology of freely-grown crystalline grains in ceramics. This mechanism can help explain the phenomena shown in our experiments and reported in many literatures, according to which the growth arts of single crystals can be improved.更多还原