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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >Phase stability of a garnet-type lithium ion conductor Li_7La_3Zr_2O_(12)
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Phase stability of a garnet-type lithium ion conductor Li_7La_3Zr_2O_(12)

机译：石榴石型锂离子导体Li_7La_3Zr_2O_（12）的相稳定性

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摘要

The phase stability of Li_7La_3Zr_2O_(12) (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 °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 °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 °C in air by absorbing CO_2 into the structure. The preferred temperature for the CO_2 absorption process was around 200 °C and the absorbed CO_2 was extracted once the temperature reached 450 °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 La_2Zr_2O_7 and La_2O_3 effectively reacted with γ-Al_2O_3 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.
机译：使用高温X射线衍射（HT-XRD）研究了Li_7La_3Zr_2O_（12）（LLZ）的相稳定性。约650°C时，无铝的四方LLZ相转变为不可淬火的立方相。四方相和新立方相之间的相变过程显示出完美的可逆性。热分析显示在640°C附近有一对吸热和放热峰，与HT-XRD研究中观察到的相变过程非常吻合。不可淬火的高温立方相显示出高离子电导率和极低的活化能（0.117 eV）。方形相通过吸收CO_2进入结构，在空气中约150-200°C时又显示出另一相转变为低温（LT）立方相。 CO_2吸收过程的优选温度为约200℃，并且一旦温度达到450℃或更高，就提取吸收的CO_2，导致相变回到四方相。另一方面，显示出高离子传导性的高温（HT）立方相通过Al取代而稳定化。含La_2Zr_2O_7和La_2O_3等杂质相的贫锂LLZ与γ-Al_2O_3有效反应，形成纯的铝稳定立方LLZ，而化学计量LLZ需要更长的时间才能完成Al的取代。结果表明，Li空位的形成是形成铝稳定的立方相的主要步骤。

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