Structure and Deuterium Desorption from Ca₃Mg₂Ni₁₃ Deuteride: A Neutron Diffraction Study

Abstract

The Ca3Mg2Ni13 unit cell can be viewed as the stacking of three blocks along the c axis. Each block is composed of two sub-blocks; one sub-block contains one layer of a [CaMgNi4] unit, and the other sub-block consists of one layer of a [CaMgNi4] unit and one layer of a [CaNi5] unit. To understand the deuterium release from the Ca3Mg2Ni13 deuteride, crystal structures of Ca3Mg2Ni13D15.6, Ca3Mg2Ni13D5.9, and Ca3Mg2Ni13D0.3 corresponding to before, during, and after deuterium desorption were determined by neutron diffraction. In Ca3Mg2Ni13D15.6, D atoms occupy interstitial sites within [CaNi5] and [CaMgNi4] units as well as sites at two unit borders. Upon deuterium desorption, the D atoms located at unit borders are released first. Then D atoms located within [CaNi5] and [CaMgNi4] units are simultaneously released which leads to the coexistence of Ca3Mg2Ni13D5.9 and a deuterium-poor solid solution phase. With further desorption, Ca3Mg2Ni13D5.9 transforms into Ca3Mg2Ni13D0.3 where D atoms reside in [CaNi5] units only.

Crystal Structure of Pr3MgNi14Dx Studied by in Situ Neutron Diffraction

“…The crystal structure of Ca 3 Mg 2 Ni 13 D 15.6 with R 3̅ m symmetry was reported by Zhang et al, , who determined the deuterium occupation in Ca 3 Mg 2 Ni 13 D 15.6 by neutron diffraction. The structural model of the deuteride is the same as that of the original alloy.…”

“…Yartys and Denys determined the crystal structure of the deuteride Pr 2 MgNi 9 with the PuNi 3 -type structure by neutron diffraction. 9 The crystal structure of Pr 2 MgNi 9 D 12.4 was refined using the PuNi 11,12 who determined the deuterium occupation in Ca 3 Mg 2 Ni 13 D 15.6 by neutron diffraction. The structural model of the deuteride is the same as that of the original alloy.…”

Crystal Structure Analysis of La2Ni6CoDx During Deuterium Absorption Process

“…The volume expansions of MgZn 2 -type cell, CaCu 5 -type cell, and the unit cell are 8.4%, 11.3%, and 10.8%, respectively. The deuterium positions and the occupation factors were determined ( Table 2) 19 The maximum deuterium capacity reached 0.87 D/M. Ca 3 Mg 2 Ni 13 D 15.6 was taken by in situ neutron diffraction at deuterium pressure 2.9720 MPa.…”

Hydrogenation Character and Crystal Structures of Hydrides in RMgNi₄ (R = Nd, Gd, Er)

“…Partial phase decomposition and amorphization of Alloys. 26) From the Fig. 4, there is no new phase or amorphous formation after hydrogen absorption and desorption.…”