Phase stability of a garnet-type lithium ion conductor Li7La3Zr2O12
Phase stability of a garnet-type lithium ion conductor Li7La3Zr2O12
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DOI：
10.1039/c3dt52024b
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发表时间：
2014-01-01
影响因子：
4
通讯作者：
Imanishi, N.
中科院分区：
文献类型：
--
作者：
Matsui, M.;Takahashi, K.;Imanishi, N.
使用高温 X 射线衍射 (HT-XRD) 研究了 Li7La3Zr2O12 (LLZ) 的相稳定性。无铝四方LLZ相在650℃左右转变为不可淬火立方相。四方相和新立方相之间的相变过程表现出完美的可逆性。热分析显示在 640 摄氏度附近有一对吸热和放热峰，这与 HT-XRD 研究中观察到的相变过程非常吻合。不可淬灭的高温立方相表现出高离子电导率和极低的活化能（0.117 eV）。通过将 CO2 吸收到结构中，四方相在空气中在 150-200 摄氏度左右表现出另一相转变为低温 (LT) 立方相。 CO2吸收过程的优选温度为200℃左右，一旦温度达到450℃或更高，吸收的CO2就会被提取，导致相变回四方相。另一方面，显示出高离子电导率的高温（HT）立方相通过Al取代而稳定。含有 La2Zr2O7 和 La2O3 等杂质相的贫锂 LLZ 与 γ-Al2O3 有效反应，形成纯铝稳定的立方 LLZ，而化学计量的 LLZ 需要更长的时间才能完成铝取代。结果表明，Li空位的形成是Al稳定立方相形成的首要步骤。
The phase stability of Li7La3Zr2O12 (LLZ) was investigated using high temperature X-ray diffraction (HT-XRD). An Al-free tetragonal LLZ phase transformed into a non-quenchable cubic phase around 650 degrees C. The phase transformation process between the tetragonal phase and the new cubic phase showed perfect reversibility. The thermal analysis showed a pair of endothermic and exothermic peaks around 640 degrees C that is in good agreement with the phase transformation process observed in the HT-XRD study. The non-quenchable high temperature cubic phase showed high ionic conductivity with extraordinarily low activation energy (0.117 eV). The tetragonal phase showed another phase transformation to a low temperature (LT) cubic phase around 150-200 degrees C in air by absorbing CO2 into the structure. The preferred temperature for the CO2 absorption process was around 200 degrees C and the absorbed CO2 was extracted once the temperature reached 450 degrees C or above resulting in the phase transformation back to the tetragonal phase. On the other hand the high temperature (HT) cubic phase which shows high ionic conductivity was stabilized by Al substitution. A Li-poor LLZ containing impurity phases such as La2Zr2O7 and La2O3 effectively reacted with gamma-Al2O3 resulting in the formation of a pure Al-stabilized cubic LLZ, while the stoichiometric LLZ took a much longer time to complete the Al-substitution. The result suggested that the formation of Li vacancies is the primary step in the formation of the Al-stabilized cubic phase.