Oxygen semi-permeation and electrical conducting behavior of electronic and oxide ionic conducting ceramics

测定了混合导电钙钛矿型氧化物La_<1-x>Sr_xCo_<0.2>Fe_<0.8>O_（3-δ）（LSCF，0.4 ≤ x ≤ 0.7）的电导率随Sr含量（x）、温度（T）和氧分压[P（O_2）]的变化。研究了LSCF的晶体结构和氧非化学计量比（δ），并与其电性能进行了关联。氧的非化学计量比和晶体中的B-O-B角（B ; B位元素）对LSCF的电导率（σ）有很大影响。通过对La_<1-x>Sr_xCo_<0.2>Fe_<0.8>O_&lt;3-δ&gt;在空气中的σ测量和晶体结构的细化，发现σ显著地依赖于B-O-B角（θ）的扩展，导致B-3d和O-2 p电子带的电子带宽展宽。氧的非化学计量比直接降低了σ，这是由于p型载流子浓度的降低，特别是在高温或低P（O_2）时。发现在临界P（O_&lt;&gt;）约为0.001以下，冻结氧空位对σ的影响很大。此外<-4>，还开发了贫Sr LSCF（La_<0.6>Sr_<0.4-y>Co_<0.2>Fe_<0.8>O_&lt;3-δ&gt;，0&lt;y ≤ 0.025），以提高氧空位浓度（δ），从而提高其氧化物离子电导率。碘量法测得δ随y的增加而增加，y=0.025的样品适合作为SOFC的阴极材料和氧气半透膜。

Electrical conductivity of mixed conducting perovskite-type oxide, La_<1-x>Sr_xCo_<0.2>Fe_<0.8>O_<3-δ> (LSCF, 0.4【less than or equal】x【less than or equal】0.7) was determined as functions of Sr-content (x), temperature (T) and oxygen partial pressure [P(O_2)]. Crystal structure and oxygen nonstoichiometry (δ) of LSCF was evaluated and correlated with its electrical property. The electrical conductivity (σ) in LSCF was greatly affected by oxygen nonstoichiometry and B-O-B angle (B ; B-site elements) in the crystal. From σ measurement and crystal structure refinement of La_<1-x>Sr_xCo_<0.2>Fe_<0.8>O_<3-δ> in air, σ is found to be significantly dependent upon the expansion of B-O-B angle (θ), inducing broadening of the electronic bandwidths of the B-3d and O-2p electronic bands. Oxygen nonstoichiometry directly reduced σ because of a decrease in the concentration of p-type charge carriers especially at elevated temperatures or low P(O_2). It was found that σ was sharply affected by the frozen oxygen vacancies below a critical P(O_<>) of ca. 6.8×10^<-4> atm at low temperatures.In addition, Sr-deficient LSCF (La_<0.6>Sr_<0.4-y>Co_<0.2>Fe_<0.8>O_<3-δ>, 0<y【less than or equal】0.025) was developed to increase oxygen vacancy concentration (δ) so as to enhance its oxide ionic conductivity. It was found that δ was increased with increase in y, determined by iodometry, and the sample of y=0.025 is suitable for cathode materials in SOFCs and oxygen semi-permeable membranes.