Phase Stability, Structural Transition, and Hydrogen Absorption−Desorption Features of the Polymorphic La4MgNi19 Compound
Phase Stability, Structural Transition, and Hydrogen Absorption−Desorption Features of the Polymorphic La4MgNi19 Compound
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DOI：
10.1021/jp103910e
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发表时间：
2010-06
影响因子：
3.7
通讯作者：
Qingan Zhang;M. Fang;T. Si;Fang Fang-Fang;Dalin Sun;L. Ouyang;Min Zhu
中科院分区：
文献类型：
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作者：
Qingan Zhang;M. Fang;T. Si;Fang Fang-Fang;Dalin Sun;L. Ouyang;Min Zhu
本工作系统地研究了多晶型La4MgNi19化合物的相稳定性、结构转变和储氢特性。 La4MgNi19化合物在840−960°C的温度范围内有两种变体，在较高温度下优选六方结构（2H），在较低温度下优选菱面结构（3R）。由于结构和组成几乎相同，2H和3R相之间的多晶型转变可以通过其亚基层的短程位移来进行。对氢化或脱氢样品的 XRD 图案的详细分析表明，2H 相的吸氢和解吸平衡压力低于 3R 相的压力，但两相之间的压力差距太小，无法从测量的压力-成分 (P-C) 等温线中识别。平均氢化和脱氢焓分别确定为 -32.1 和 31.5 kJ/mol H2...
The phase stability, structural transition, and hydrogen storage characteristics of the polymorphic La4MgNi19 compound are systematically investigated in the present work. The La4MgNi19 compound has two variants in the temperature range of 840−960 °C with a preference for a hexagonal structure (2H) at a higher temperature and a rhombohedral structure (3R) at a lower temperature. Because the structure and composition are almost identical, the polymorphic transition between the 2H and 3R phases may proceed through short-range displacements of their subunit layers. Detailed analyses on XRD patterns for the hydrided or dehydrided samples indicate that the equilibrium pressures of hydrogen absorption and desorption for the 2H phase are lower than the pressures for the 3R phase, but the pressure gap between the two phases is too small to be identified from the measured pressure−composition (P−C) isotherms. The average hydriding and dehydriding enthalpies are determined to be −32.1 and 31.5 kJ/mol H2, respective...