Diffusion Path and Conduction Mechanism of Oxide Ions in Apatite-Type Lanthanum Silicates
Diffusion Path and Conduction Mechanism of Oxide Ions in Apatite-Type Lanthanum Silicates
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DOI：
10.1021/cm900783j
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发表时间：
2009-06-23
影响因子：
8.6
通讯作者：
Champion, Eric
中科院分区：
文献类型：
--
作者：
Bechade, Emilie;Masson, Olivier;Champion, Eric
通式为La9.33+2x/3(SiO4)(6)O2+x的磷灰石型硅酸镧是最近出现的一类新型氧化物离子导体，具有潜在的固体氧化物燃料电池(SOFC)电解质应用前景。它们在中等温度和低氧分压下表现出相对较高的氧离子导电性。本文重新研究了氧化物离子在这些相中的扩散途径和传导机制。这是通过原子尺度的计算机模拟技术和半经验方法和键价方法来完成的。我们的结果支持氧化物离子沿c轴的传导是通过间隙机制进行的。它们还支持位于传导通道内的间隙位置的存在。然而，与最近的研究相反，研究表明，沟道氧离子以推挽机制参与了导电过程。这一机制发挥了形成复杂缺陷的两个相邻间隙氧化物离子和沟道氧化物离子的协同运动。这种复杂的缺陷是通过一条不同于文献中提出的传导路径的非线性路径沿c轴移动的。计算得到该机制的迁移能为0.32 eV，与沿c轴测量的Nd9.33(SiO4)(6)O-2单晶的激活能相当接近。
Apatite-type lanthanum silicates of general formula La9.33+2x/3(SiO4)(6)O2+x have appeared recently as a new promising class of oxide ion conductors with potential applications as electrolytes for solid oxide fuel cells (SOFCs). They have been shown to demonstrate relatively high oxide ion conductivity at moderate temperatures as well as at low oxygen partial pressures. In this paper, the diffusion pathways and the conduction mechanism of oxide ions in these phases are reinvestigated. This is done by means of atomic scale computer modeling techniques with both semiempirical and bond valence methods. Our results support that oxide ion conduction along the c-axis proceeds by an interstitial mechanism. They also support the presence of interstitial sites located within the conduction channel. However, contrarily to recent research, it is shown that the channel oxide ions are involved in the conduction process by a push-pull type mechanism. This mechanism brings into play a cooperative movement of both two adjacent interstitial oxide ions forming a complex defect and the channel oxide ions. This complex defect is shown to move along the c-axis via a nonlinear pathway different from the conduction path proposed in literature to date. The calculated migration energy of this mechanism is found to be equal to 0.32 eV, which compares well with activation energy measured along the c-axis for Nd-9.33(SiO4)(6)O-2 single crystals.