碱土和过渡金属掺杂NdAlO_3导电陶瓷的制备、结构与电性能研究

Preparation, structures and electrical properties of alkaline earth and transition metal-doped NdAlO_3 conducting ceramics

采用有机凝胶法结合后期高温烧结制备了较为致密的六方钙钛矿结构Nd0.9Sr0.1Al1-xMxO3-δ(M=Co,Fe,Mn;x=0,0.15,0.3,0.5)系列陶瓷,详细研究了过渡金属元素及掺杂量对其结构特征和电性能的影响.结果表明,凝胶前驱体在900℃焙烧5h可制得结晶良好且粒径较为细小的钙钛矿结构精细粉体,陶瓷体的晶格参数随过渡金属含量x的增加而增大,且按Co,Mn,Fe顺序递增;所有陶瓷样品在空气气氛中都是氧离子与电子空穴的混合导体,碱土金属Sr单掺杂NdAlO3的氧离子迁移数由500℃时的0.32单调增加到850℃时的0.63,其电导率随温度的升高由以电子电导为主逐渐转变为以离子电导为主;而Sr与过渡金属共掺杂样品的氧离子迁移数均在0.001以下,其电导率主要取决于p型电导,且随x的增加而增大,并按Mn,Fe,Co顺序递增,相应活化能的变化刚好与之相反,在所制备的样品中Nd0.9Sr0.1Al0.5Co0.5O3-δ具有最高的电导率(800℃时达到100.8S/cm)和最低的表观活化能(0.135eV).在结构和电性能上所观察到的这些变化行为可根据掺杂过渡金属Co,Fe,Mn的离子半径及其金属-氧(M—O)键的键能和共价性的不同来进行解释.

Novel Nd0.9Sr0.1Al1-xO3-δ（M=Co,Fe,Mn;X=0,0.15,0.3,0.5） conducting ceramics each with a hexagonal perovskite structure are prepared using organic-gel method combined with subsequent high temperature sintering. The influences of transition elements （Co, Fe, and Mn） and their dosages on the structure characteristics and electrical properties are investigated in detail. The experimental results reveal that well-crystallized Nd0.9Sr0.1All-xMxO3-δ perovskite oxide ultrafine powders can be obtained by calcining the gel precursors at 900 ℃ for 5 h. The lattice parameters of sintered ceramics increase with the increase of transition metal content （x）, and they increase according to the order of Co, Mn, and Fe. All the samples are mixed conductors of oxygen ions and holes in air, and the oxygen ion transport number is enhanced monotonically from 0.32 at 500 ℃ to 0.63 at 850 ℃ for NdAlO3-δ ceramic single-doped with alkaline earth metal Sr, indicating that this material has an electronic-to-ionic dominant transition in electrical conductivity with measurement temperature increasing. Whereas the oxygen ion transport numbers are all below 0.001 for the samples co-doped with Sr and transition metals （Co, Fe, and Mn）, and their electrical conductivities are absolutely dominated by p-type conduction. It is found that the conductivity values increase with the increase ofx value, and they increase according to the order of Mn, Fe, and Co, while the change of corresponding apparent activation energies is just the opposite. Nd0.gSr0.1Al0.5Co0.5O3-δ ceramic has the highest electrical conductivity, -100.8 S/cm at 800 ℃, and the lowest apparent activation energy （0.135 eV） in all the synthesized samples. The observed changes in structure and electrical property in this study can be explained on the basis of the difference in ionic radii among the doped transition metals as well as the differences in bond energies and covalencies among the M-O bonds.