Hydride ion as a two-electron donor in a nanoporous crystalline semiconductor 12CaO•7Al2O3
Hydride ion as a two-electron donor in a nanoporous crystalline semiconductor 12CaO•7Al2O3
复制标题
DOI：
10.1021/jp053990p
复制
发表时间：
2005-12-22
影响因子：
3.3
通讯作者：
Hosono, H
中科院分区：
文献类型：
--
作者：
Hayashi, K;Sushko, PV;Hosono, H
具有纳米多孔晶格框架的12 CaO中心点7Al（2）O（3）（C12 A7）晶体当在高于类似于800 ℃的氢气氛中平衡时表现出高电导率，其活化能类似于1.5eV。高电导率在低于类似于600摄氏度的淬火状态下保持，具有类似于0.8eV的降低的活化能。电导率的这种复杂行为与氢离子（H-）在晶格框架的笼中的掺入有关。电动势的测量表明，导电性的主要载体是电子与质子（H+）的贡献很小，排除了直接笼间离子的可能性。这些观察结果与从头计算的结合导致H的迁移结论，即电子是通过解离成两个电子和一个质子从H-离子热产生的，质子通过与骨架外氧化物离子（O2-）反应进一步转化为OH-离子。通过理论计算评估的初始（H- + O2-）和最终（2 e（-）+ OH-）状态之间的能量差小至类似于1 eV，这与实验获得的焓变（类似于1.4eV）非常一致。因此，骨架外氢和氧物种之间的内部平衡负责载电子的热产生.这也表明，同样的导电（2 e（-）+ OH-）状态通过光照射含H-的C12 A7达到.在这种情况下，H-的光电离形成一个电子和一个H-O原子，然后在热辅助下形成一个OH-离子和另一个电子。光诱导电导率的持久性是由在室温下的反向过程的缓慢动力学解释的。
The 12CaO center dot 7Al(2)O(3) (C12A7) crystal with a nanoporous lattice framework exhibits high electrical conductivity with an activation energy of similar to 1.5 eV when equilibrated in a hydrogen atmosphere above similar to 800 degrees C. The high conductivity is preserved in a quenched state below similar to 600 degrees C with a reduced activation energy of similar to 0.8 eV. Such complex behavior in electrical conductivity is associated with incorporation of hydride ions (H-) in cages of the lattice framework. Electromotive force measurements reveal that the major carrier for the conductivity is electron with a small contribution by proton (H+), ruling out the possibility of direct intercage ion. A combination of these observations with the ab initio calculations leads to the migration of the H conclusion that the electrons are thermally generated from the H- ion by the dissociation into two electrons and an proton, which is further converted to an OH- ion via reaction with an extraframework oxide ion (O2-). The energy difference between the initial (H- + O2-) and the final (2e(-) + OH-) states as evaluated by the theoretical calculation is as small as similar to 1 eV, which agrees well with an experimentally obtained enthalpy change, similar to 1.4 eV. Thus, internal equilibration between the extraframework hydrogen and the oxygen species is responsible for the thermal generation of the carrier electron. It is also suggested that the same conductive (2e(-) + OH-) state is reached by the photoirradiation of H--containing C12A7. In this case the photoionization of H- forms an electron and an H-o atom, which then forms an OH- ion and another electron with thermal assistance. The persistence of photoinduced conductivity is explained by the slow kinetics of the reverse process at room temperature.