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_&lt；1-x&gt；Sr_xCo_&lt；0.2&gt；Fe_&lt；0.8&gt；O_&lt；3-δ&gt；(LSCF，0.4[小于或等于]x[小于或等于]0.7)的电导率与锶含量(X)、温度(T)和氧分压[P(O2)]的关系。对LSCF的晶体结构和氧非化学计量比(δ)进行了评价，并与其电学性质进行了关联。LSCF的电导率(σ)受晶体中氧的非化学计量比和B-O-B角(B位元素)的影响很大。通过La_&lt；1-x&gt；Sr_xCo_&lt；0.2&gt；Fe_&lt；0.8&gt；O_&lt；3-δ&gt；在空气中的σ测量和晶体结构修正，发现σ明显依赖于B-O-B角(θ)的扩展，从而导致B-3d和O-2p电子能带的展宽。氧的非化学计量比直接降低了σ，这是因为p型载流子浓度的降低，特别是在高温或低P(O2)时。结果表明，低温下临界P(O&t；-4 atm)以下的冻结氧空位对(La_&lt；0.6&gt；Sr_&lt；0.4-y&gt；Co_&lt；0.2&gt；Fe_&lt；0.8&gt；O_&lt；3-δ&gt；，的影响很大。此外，缺锶σ0&lt；Y[小于或等于]0.025)是为了提高氧空位浓度(δ)以增强其氧化物离子电导率而开发的。用碘量法测定，δ随y的增加而增大，y=0.025的样品适合作为固体氧化物燃料电池和氧气半透膜的正极材料。

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.