The present work is focused on the studies of the phase-structural transformations in the La_3-xMg_xNi₉ (x ​= ​1.0, 1.1 and 1.2) alloys as active materials of negative electrodes in the Nickel-Metal Hydride (Ni/MH) batteries. The phase equilibria and phase-structural transformations in the alloys were probed by in situ neutron powder diffraction (NPD) at the temperatures ranging from 300 ​K to 1273 ​K using the measurements of the equilibrated alloys at 8 setpoint temperatures of 300, 973, 1073, 1123, 1173, 1223, 1248 and 1273 ​K.

Prepared by induction melting initial alloys were found to be multi-phase structured, containing up to 6 individual intermetallic compounds with different stoichiometric compositions. With the increase of the temperature and holding time, various transformations took place in the studied alloys. These included the formations and transformations of super-stacking intermetallics with variable ratios (La ​+ ​Mg)/Ni, 1:3, 2:7 and 5:19.

With increasing temperatures, several systematic changes took place. (a) Abundances of (La,Mg)₂Ni₄ AB₂ and (La,Mg)Ni₃ AB₃ type intermetallics gradually decreased before they melted/decomposed above 1073 ​K; (b) The (La,Mg)₂Ni₇ A₂B₇ type intermetallics began to decrease in abundances above 1123 ​K; (c) The transformation in the (La,Mg)₅Ni₁₉ intermetallics from 3R to 2H proceeded above 1223 ​K.

The increase of Mg content had no obvious influence on (La,Mg)₂Ni₄ and (La,Mg)₂Ni₇ phases, and corresponding reactions R1 and R3 took place at the same temperatures as in the La–Ni system. However, with increasing Mg content the melting point of (La,Mg)₅Ni₁₉ phase increased while the melting point of the (La,Mg)Ni₃ phase it decreased, leading to the variation of the reaction temperatures of the corresponding processes.

The present study will assist in optimizing phase-structural composition of the alloys in the La–Mg–Ni system which contain Mg-modified layered structures by tailoring the high temperature annealing conditions.

目前的工作集中在相结构转变的研究中的La _3-x Mg的_X镍₉（X = 1.0，1.1和1.2）的合金作为镍-金属氢化物负电极的活性材料（镍/MH) 电池。合金中的相平衡和相结构转变通过原位中子粉末衍射 (NPD) 在 300 K 至 1273 K 的温度范围内使用平衡合金在 8 个设定点温度 300、973、 1073、1123、1173、1223、1248 和 1273 K。

发现通过感应熔化制备的初始合金是多相结构的，包含多达 6 种具有不同化学计量组成的独立金属间化合物。随着温度和保温时间的增加，所研究的合金发生了各种转变。其中包括具有可变比率 (La + Mg)/Ni、1:3、2:7 和 5:19 的超级堆叠金属间化合物的形成和转变。

随着温度的升高，发生了一些系统性变化。(a) (La,Mg) ₂ Ni ₄ AB ₂和(La,Mg)Ni ₃ AB ₃型金属间化合物的丰度在1073 K以上熔化/分解之前逐渐减少；(b) (La,Mg) ₂ Ni ₇ A ₂ B ₇型金属间化合物的丰度在 1123 K 以上开始减少；(c) (La,Mg) ₅ Ni ₁₉金属间化合物从 3R 到 2H的转变在1223 K 以上进行。

Mg含量的增加对(La,Mg) ₂ Ni ₄和(La,Mg) ₂ Ni ₇相没有明显影响，相应的反应R1和R3发生在与La-Ni体系相同的温度下。然而，随着Mg含量的增加，(La,Mg) ₅ Ni ₁₉相的熔点升高，而(La,Mg)Ni ₃相的熔点降低，导致相应过程的反应温度发生变化。

本研究将有助于通过调整高温退火条件来优化含有 Mg 改性层状结构的 La-Mg-Ni 系统中合金的相结构组成。