Crystal structure and hydrogen absorption–desorption properties of Ca3Mg2Ni13

Abstract The novel compound Ca 3 Mg 2 Ni 13 has been found in the Ca–Mg–Ni system, and its crystal structure has been investigated by X-ray diffraction and high-resolution transmission electron microscopy. Ca 3 Mg 2 Ni 13 crystallizes in space group R 3 ¯ m (No. 166); cell parameters: a = 4.9783(2) A and c = 36.180(2) A; Z = 3. The Ca 3 Mg 2 Ni 13 structure has three blocks stacked along the c axis in one period, and each block is composed of two sub-blocks. One only contains one layer of [CaMgNi 4 ] units, and the other consists of one layer of [CaMgNi 4 ] units and one layer of [CaNi 5 ] units. Further investigations show that Ca 3 Mg 2 Ni 13 has good kinetic properties but bad thermodynamic properties for hydrogen absorption–desorption. However, the Ca/Mg ratio of the Ca 3 Mg 2 Ni 13 -type compound can be adjusted within a wide range to improve the hydrogen absorption–desorption properties. As a result, Ca 1.67 Mg 3.33 Ni 13 shows favorable thermodynamics and has good reversibility for hydrogen absorption–desorption.