Synthesis And Properties Of Novel Aluminate-based Conducting Ceramics

Mixed ionic and electronic conducting ceramics had received a great attention sincethey can used in valuable and promising applications such as solid o_xide fuel cell, protonexchange membrane fuel cell, o_xygen separation membrane, hydrogen separationmembrane, membrane reactor, sensor and so on.In this dissertation, we prepared the Ln_0.9Sr_0.1Al_1–xM_xO_3–δ（Ln=Sm, Nd, Pr；M=Co, Mn,Fe, Cr） conducting ceramics by the organic gel process and subsequent densificationsintering and discussed the effects of sintering parameters, transition metal types, anddoping concentration on the structure, phase composition and electrical properties.1. Well-crystallized perovskite o_xide nanopowders can be obtained by calcining the gelprecursors at900℃for5h. The high relative density ceramics can be obtained through thesintering of the precursor powers. The relative density and conductivity gradually increasewith sintering temperature. However, if the sintering temperature is more than a certainvalue, the relative density and conductivity would be decreased.2. The lattice volume generally increases with the doping concentration of thetransition metals. This is due to the larger ionic radius of the transition metals than the ionicradius of Al³⁺. Additionally, the lattice volume increases with the ionic radius of the dopedmetals in the same series of ceramics. There is an abnormal change in theSm_0.9Sr_0.1Al_1-xCr_xO_3-δseries ceramics, the lattice parameters decrease with the increase Crcontent when x≤0.2. Beside that, the lattice parameters of Pr_0.9Sr_0.1Al_1-xCo_xO_3-δceramicsdecrease suddenly when the Co content x=0.5, and the value is smaller that x=0.3. The conductivities of the ceramics increase with the doping concentration of thetransition metals, and increase in the order Cr, Mn, Fe, Co, while the change of thecorresponding activation energy of is just opposite. The observed changes can be explainedby the ionic radius of the transition metals, the bond energies and covalencies of the M-Obonds. The conductivities of the Sm_0.9Sr_0.1Al_1-xCr_xO_3-δseries ceramics has an abnormalchange as the x=0.2has a smaller conductivity and a larger corresponding activation energythan x=0.1.