Investigation of the phase occurrence, H sorption properties, and electrochemical behavior in the composition ranges La0.75-0.80Mg0.30-0.38Ni3.67

Junxian Zhang (1) , Michel Latroche (1) , Cesar Magen (2) , Virginie Serin (3) , Martin Hÿtch (3) , Bernard Knosp (4) , Patrick Bernard (4)

1 CMTR - Chimie métallurgique des terres rares
2 Universidad de Zaragossa
3 CEMES - Centre d'élaboration de matériaux et d'études structurales
4 SAFT, Direction de la Recherche

To explore the possible occurrence of new stacking sequences within the La-Mg-Ni system, two alloys in the composition range La15.6-16.8Mg6.3-7.8Ni76.5-76.9 (at. %) have been synthesized by Spark Plasma Sintering (SPS). The X-ray diffraction analyses show that the obtained alloys contain a mixture of A2Ni7 and A5Ni19 phases (A = La, Mg) with coexistence of hexagonal and rhombohedral polymorphs. Such structures can be described as a stacking along the c crystallographic axis of mAB5 units (labeled C) and nA2B4 units (labeled L). Up to now, compounds with 1 ≠ m ≠ 4, but only n = 1 were confirmed in the La-Mg-Ni system. One composition has been particularly studied here by High-Angle Annular Dark-Field (HAADF) Scanning Transmission Electron Microscopy (STEM). A continuous change of the stacking sequences (from C + L to 4C + L) is observed within a 50 nm region. In addition, two types of stacking faults (twinning and dislocation) have been revealed. The expected stacking sequence with n > 1 has not been observed in the present work. The hydrogen storage capacity and the electrochemical capacity are not significantly affected by the phase compositions, while the cyclic stability appears particularly sensitive to the Mg content.

Mots clés: Hydrogen storage; Scanning electron microscopy; Spark plasma sintering; Stacking faults; Transmission electron microscopy; X ray diffraction; X ray diffraction analysis; Composition ranges; Crystallographic axis; Electrochemical behaviors; Electrochemical capacities; H-sorption properties; High-angle annular dark fields; Hydrogen storage capacities; Scanning transmission electron microscopy; Nickel

Domaines: Physique [physics]

Junxian Zhang, Michel Latroche, Cesar Magen, Virginie Serin, Martin Hÿtch, et al.. Investigation of the phase occurrence, H sorption properties, and electrochemical behavior in the composition ranges La0.75-0.80Mg0.30-0.38Ni3.67. Journal of Physical Chemistry C, 2014, 118 (48), pp.27808-27814. ⟨10.1021/jp510313a⟩. ⟨hal-01760672⟩