La-Mg-Ni/Co储氢合金中的相结构

应用真空电弧熔炼方法制备La-Mg-Ni/Co5：19和2：7型储氢合金.应用X射线衍射系统研究这两类合金的相结构,并测定各相的原子占位.研究表明：5：19型的（La1-xMgx）5Co19合金是由Pr5Co19,LaCo5和LaSb3V3种类型结构组成;在2：7型的（La1-xMgx）2Ni7合金中,除了（La0.85Mg0.15）2Ni7合金只含LaNi5类型相结构外,其他合金均含有LaNi5类型相结构及LaNi3或La2Ni7类型相之一.应用尝试法确定合金中各相的晶胞参数和体积的变化规律,并利用Rietveld全谱拟合分析方法测定了（La0.95Mg0.05）2Ni7合金的相结构及相含量.研究表明：两种储氢合金相结构中主相与晶界相的点阵常数之间存在良好的共格性.Mg原子同时部分取代La和Ni原子,随着Mg含量的增加,晶胞内空隙变大.由于吸收的H原子将占据这些空位,所以空位空间的增加有助于容纳更多的H.这暗示Mg原子的占位导致的晶体畸变与储氢合金储氢能力相关,同时由于Mg原子与H原子之间强的亲和力,以及主相与晶界相之间的共格关系,可以使得H原子更容易进人合金中,并形成稳定的相结构.

Phase structures of the La-Mg-Ni/Co hydrogen storage alloys

La-Mg-Ni/Co hydrogen storage alloys with 5：19 and 2：7 type structures were prepared using vacuum arc melting technology. The powder X-ray diffraction was employed to study the phase structures of these hydrogen storage alloys. The results show that the three phases with structural types of Pr5Co19, LaCo5 and LaSb3V coexist in 5：19 alloys and LaNis, LaNi3 and La2Ni7 phase coexist in 2：7 alloys. The TREOR program was used to determine the lattice parameters and cell volumes of the phases in the two alloys. A Rietveld structural refinement technology was used to determine the atomic occupations and phase concentrations. The lattice spacings among the atoms tend to increase with increasing Mg contents in the two alloys, which increases the entrances possibilities of hydrogen atoms in atomic spaces. Meanwhile, the lattice parameters show a good coherency among the phases in alloys. It implies that the lattice distortions induced by Mg doping is beneficial for increasing the hydrogen storages contents.