In Situ X-ray Diffraction Study of Phase Transformation of Mg_2–xPr_xNi₄ during Hydrogenation and Dehydrogenation (x = 0.6 and 1.0)

Abstract

The phase transformations of Mg 1.4 Pr 0.6 Ni 4 and Mg 1.0 Pr 1.0 Ni 4 during hydrogenation and dehydrogenation were investigated using in situ X-ray diffraction (XRD). Both alloys showed the cubic MgCu 4 Sn type structure with space group F43m before hydrogenation. The hydride β-Mg 1.4 Pr 0.6 Ni 4 H ∼3.6 had the same crystal structure as the starting alloy, and its lattice was expanded by 4.3% by hydrogenation. Mg 1.0 Pr 1.0 Ni 4 was initially transformed to an orthorhombic β-Mg 1.0 Pr 1.0 Ni 4 H ∼4 with space group Pmn2 1 . By further hydrogenation, the orthorhombic hydride changed to γ-Mg 1.0 Pr 1.0 Ni 4 H ∼6 with a cubic structure with space group F43m. The lattice constant of γ-Mg 1.0 Pr 1.0 Ni 4 H ∼6 was 7.6% larger than that of the starting alloy. Through dehydrogenation, all hydride phases returned to the alloy phase without any amorphization or disproportionation.

TbMgNi4-xCox–(H,D)2 System. I: Synthesis, Hydrogenation Properties, and Crystal and Electronic Structures

“…2) resemble those obtained for isostructural LaMgNi 4 31 and CeMgCo 4 19 compounds, where formation of the α-, β-, γ-hydrides have been also observed. For RMgNi 4-x Co x compounds [19][20][21][22][23]29,30 only one plateau has been observed. Moreover, for the (Nd,Pr) 1-y La y MgNi 4-x Co x alloys, La and Co substitution initiates an easiest way to observe the β → γ transformation at 10 bar H 2 22,23 .…”

“…Similar results were obtained for Pr-and Pr 0.5 La 0.5 -containing alloys 23 . [20][21][22][23]29,30 . PCT curves with two plateaus for the TbMgNi 4-x Co x compounds (x ≥…”

Solid gas and electrochemical hydrogenation of the selected alloys (R’,R’’)2-Mg Ni4-Co (R’, R’’ = Pr, Nd; x = 0.8–1.2; y = 0–2)

“…The maximum discharge capacity of 400 mAh/g is established by the authors [8]. Although there are many studies on the hydrogen adsorption properties of the RMgM 4 containing alloys [9], a comprehensive study of the single-phase RMgM 4 samples is limited to a few dozen works, most of which are devoted to the study of stoichiometric compositions [10][11][12][13][14][15][16][17][18].…”

Solid gas and electrochemical hydrogenation properties of the R1-xR’xMgNi4-yCoy (R, R’ = Y, La, Ce) alloys

“…Basically obtained materials are the mixtures of Laves AB2, Haucke AB5 or/and superlattice (AB2)n(AB5)m phases. Among them the RMgNi4 phases are characterized by good solid gas and electrochemical properties and can be easily prepared by sintering or induction melting methods [6][7][8][9][10][11][12][13][14][15][16][17][18]. Recently, the YMgNi4-xCox [19], LaMgNi4-xCox [20], NdMgNi4-xCox [21], La1-xNdxMgNi4-yCoy [22] and Pr1-xLaxMgNi4-yCoy [23] alloy systems were systematically investigated in our research group.…”