Ishihara T, Arikawa H, Akbay T, Nishiguchi H, Takita Y
Contribution from the Department of Applied Chemistry, Faculty of Engineering, Oita University, Dannoharu 700, Oita 870-1192, Japan.
J Am Chem Soc. 2001 Jan 17;123(2):203-9. doi: 10.1021/ja0014537.
Oxide ion conductivity in La(2)GeO(5)-based oxide was investigated and it was found that La-deficient La(2)GeO(5) exhibits oxide ion conductivity over a wide range of oxygen partial pressure. The crystal structure of La(2)GeO(5) was estimated to be monoclinic with P2(1)/c space group. Conductivity increased with increasing the amount of La deficiency and the maximum value was attained at x = 0.39 in La(2 - x)GeO(5 - delta). The oxide ion transport number in La(2)GeO(5)-based oxide was estimated to be unity by the electromotive force measurement in H(2)-O(2) and N(2)-O(2) gas concentration cells. At a temperature higher than 1000 K, the oxide ion conductivity of La(1.61)GeO(5 - delta) was almost the same as that of La(0.9)Sr(0.1)Ga(0.8)Mg(0.2)O(3 - delta) or Ce(0.85)Gd(0.15)O(2 - delta), which are well-known fast oxide ion conductors. On the other hand, a change in the activation energy for oxide ion conductivity was observed at 973 K, and at intermediate temperature, the oxide ion conductivity of La(1.61)GeO(5 - delta) became much smaller than that of these well-known fast oxide ion conductors. The change in the activation energy of the oxide ion conductivity seems to be caused by a change in the local oxygen vacancy structure. However, doping a small amount of Sr for La in La(2)GeO(5) was effective to stabilize the high-temperature crystal structure to low temperature. Consequently, doping a small amount of Sr increases the oxide ion conductivity of La(2)GeO(5)-based oxide at low temperature.
对基于La₂GeO₅的氧化物中的氧离子传导性进行了研究，发现缺La的La₂GeO₅在很宽的氧分压范围内表现出氧离子传导性。据估计，La₂GeO₅的晶体结构为单斜晶系，空间群为P2(1)/c。电导率随着La缺陷量的增加而增加，在La(2 - x)GeO(5 - δ)中，当x = 0.39时达到最大值。通过在H₂ - O₂和N₂ - O₂气体浓差电池中的电动势测量，估计基于La₂GeO₅的氧化物中的氧离子迁移数为1。在高于1000 K的温度下，La₁.₆₁GeO(5 - δ)的氧离子传导率与La₀.₉Sr₀.₁Ga₀.₈Mg₀.₂O(3 - δ)或Ce₀.₈₅Gd₀.₁₅O(2 - δ)几乎相同，这两种都是著名的快氧离子导体。另一方面，在973 K时观察到氧离子传导率的活化能发生了变化，在中间温度下，La₁.₆₁GeO(5 - δ)的氧离子传导率比这些著名的快氧离子导体小得多。氧离子传导率活化能的变化似乎是由局部氧空位结构的变化引起的。然而，在La₂GeO₅中用少量的Sr掺杂La对将高温晶体结构稳定到低温是有效的。因此，掺杂少量的Sr会增加基于La₂GeO₅的氧化物在低温下的氧离子传导率。
