Effect of Rare Earth Elements and Alloy Composition on Hydrogenation Properties and Crystal Structures of Hydrides in Mg_2–xRE_xNi₄

Abstract

The effect of the rare earth elements and alloy composition on the hydrogenation properties and crystal structures of hydrides in Mg2–x RE x Ni4 (RE = La, Pr, Nd, Sm, and Gd; x = 0.6 and 1.0) was investigated. All Mg2–x RE x Ni4 alloys had a C15b Laves phase before hydrogenation. Mg1.4 RE 0.6Ni4 (RE = Pr, Sm, and Gd) alloys were hydrogenated through one plateau to form Mg1.4 RE 0.6Ni4H∼3.6 while maintaining the C15b structure. Mg1.0 RE 1.0Ni4 (RE = La, Pr, and Nd) alloys were hydrogenated to ∼1.0 H/M proceeding through two plateaus, and Mg1.0 RE 1.0Ni4 (RE = Sm and Gd) alloys were hydrogenated to 0.6–0.7 H/M through one plateau. Mg1.0 RE 1.0Ni4 alloys initially transformed into Mg1.0 RE 1.0Ni4H∼4 with an orthorhombic structure. In addition it was experimentally confirmed that Mg1.0 RE 1.0Ni4H∼4 with La, Pr, and Nd transformed into Mg1.0 RE 1.0Ni4H∼6 with a C15b structure, while no formation of Mg1.0 RE 1.0Ni4H∼6 (RE = Sm and Gd) was observed at 40 MPa at 250 K. Theoretical calculations suggest that Mg1.0 RE 1.0Ni4H∼4 with Sm and Gd also transform to Mg1.0 RE 1.0Ni4H∼6 at higher pressures than those used in our experiments (264 MPa for Mg1.0Sm1.0Ni4 and 8.5 GPa for Mg1.0Gd1.0Ni4 at 253 K). It was found that the hydrogenation properties and crystal structure of the hydrides in Mg2–x RE x Ni4 are dependent on the alloy composition, i.e., the ratio of Mg to RE in the alloy phase, but independent of the choice of rare earth element.

Hydrogenation Properties of Ternary Intermetallic Compounds Mg_2&minus;<i>_x</i>Pr<i>_x</i>Ni₄

“…The detailed structures of the two hydrides, MgPrNi 4 H ³4 and MgPrNi 4 H ³6 , will be reported elsewhere. 14) XRD profiles of Mg 0.8 Pr 1.2 Ni 4 and Mg 0.6 Pr 1.4 Ni 4 after hydrogenation indicate that hydrogeninduced amorphization occurred in these compositions. Aoki et al 15,16) indicated that the ratio of the atomic radii, R A /R B , is a dominant factor for controlling the hydrogeninduced amorphization, where R A and R B are the atomic radii of A and B atoms in C15-type AB 2 …”

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.…”

Solid gas and electrochemical hydrogenation properties of the selected R,R’MgNi4-xMx (R,R’ = La, Pr, Nd; M = Fe, Mn; x = 0.5, 1) alloys

“…Highest discharge capacity of the electrodes for these materials can reach 400 mAh/g [3]. Although there are many studies on the hydrogen adsorption properties of the multi phase alloys which containg RMgM4 intermetallics [4], a comprehensive study of single-phase RMgM4 samples is limited to a few dozen works, most of which are devoted to the study of stoichiometric 1:1:4 composition [5][6][7][8][9][10][11][12][13]. In our recent studies we shown the effect of the rare earth and transition metals substitution on the hydrogen sorbtion properties based on the LaMgNi4 compound [14][15].…”