多晶β″-Al_2O_3的稀土离子交换——Ⅲ.电导性能研究

Ion Exchange of Polycrystalline β″-Al_2O_3 with Rare Earth Ions——Ⅲ.Electrical Properties

由 Naβ″-Al_2O_3通过离子交换得到了 Ce^(3+)β″-Al_2O_3和 Eu^(2+)β″-Al_2O_3陶瓷。测定表明,不同条件下制备的 Eu^(2+)β″-Al_2O_3样品均具有较好的导电性,而 Ce^(3+)β″-Al_2O_3导电性较差。Eu^(2+)β″-Al_2O_3的δ_(300)℃>1×10^(-3)(Ω·cm)^(-1),其电导率—温度曲线上～300℃处出现明显的转折,活化能相应地从0.88eV 减小到0.22eV。实验发现,当少量的 Na^+被 Eu^(2+)离子交换后,引起电导率急剧下降;交换率>19.9%后,电导率基本不变。根据混合离子 Na^+-Eu^(2+)β″-Al_2O_3的电学特性提出了 Eu^(2+)离子交换的模型。

Eu^(2+)-β″Al_2O_3 ceramics obtained by the ion exchange method under differentconditions exhibited ionic conductivity greater than 1×10^(-3)(Ω·cm)^(-1) at 300℃.The bending of the Arrhenius plot occured at about 300℃,with the activationenergy decreasing from 0.88eV to 0.22eV.The conductivity was reduced sharplywhen a few Eu^(2+) ions replaced Na^+ ions,but practically unchanged after the rateof ion exchange (f) greater than 19,9%.A model for the ion exchange of Na^+ byEu^(2+) was proposed which assumed that Eu^(2+) ions would preferentially occupy mOsites and be combined with near BR vacancies.Thus the conduction of Na^+ isrestrained.As temperature increasing,the binding strength is weakened,so thereducing effect of Eu^(2+) becomes weaker.Ce^(3+) β″-Al_2O_3 ceramics were also preparedby ion exchange method,but the conductivities were considerably low.