储氢合金La0.67Mg0.33Ni2.5Co0.5及其氘化物的

Crystal Structure of Hydrogen Storage Alloy La0.67Mg0.33Ni2.5Co0.5 and Its Deuteride La0.67Mg0.33Ni2.5Co0.5D4.0

摘要:

用X射线衍射(XRD)、中子衍射(NRD)和Rietveld全谱拟合方法分析和研究PuNi3型La0.67Mg0.33Ni2.5Co0.5合金及其充氘后的氘化物晶体结构。结果表明，退火合金La0.67Mg0.33Ni2.5Co0.5由主相(La, Mg)Ni3相(PuNi3-type)和少量LaMgNi4相(MgCu4Sn-type) 及La2Ni7相(Ce2Ni7-type)组成；Co元素在(La, Mg)Ni3相中主要分布在AB5单元中6c和AB5 /AB2单元共格处的18 h位置上；合金充满氘后形成了La0.67Mg0.33Ni2.5Co0.5D4.0，D原子在(La, Mg)Ni3相中主要占据RM5单元中的36i2、18h5、6c4及RM2单元内的6c1、18h3和18h1位置上，其中RM5单元中的氘含量为6.5(1)D/ f.u.，而RM2单元中吸纳的氘量为3.2(2)D/ f.u.。充氘后La0.67Mg0.33Ni2.5Co0.5D4.0晶胞整体基本呈各向同性膨胀(δa/a＝7.1%，δc/c=9.1%)，但在RM2单元中其各向异性膨胀较大(δc/c =15.8%，δV/VRM2=32.8%)，而在RM5单元中各向异性膨胀较小(δc/c=2 .4%，δV/VRM5=17.5%)

Abstract:

Crystal structure of annealed alloy La0.67Mg0.33Ni2.5Co0.5 and (La0.67Mg0.33Ni2.5Co0.5)D4.0 deuterides were studied by X-ray diffraction, neutron diffraction and Rietveld refinement. It is found that the alloys are mainly composed of (La,Mg)Ni3 phase with rhombohedra PuNi3 type (space group: R3m) structure, and the second phases are LaMgNi4 phase (MgCu4Sn type) and La2Ni7 phase (Ce2Ni7 type). In the (La,Mg)Ni3 phase, the Mg atoms only occupy at 6c sites in the RM2 unit, while the Co atoms mainly occupy at 18 h in the RM5 unit and 6c positions in the boundary between the RM5 and RM2 blocks. The full deuteride of the main phase (La0.67Mg0.33Ni2.5Co0.5)D4.0 has a rhombohedral structure. For the (La0.67Mg0.33Ni2.5Co0.5)D4.0 deuteride, the significant occupancy of deuterium atoms are mainly six sites: 6c1, 18h3 and 18h1 within the RM2 units and 36i2, 18h5, 6c4 within the RM5 units. At the same time, it is found that the 6.5(1)D/f.u. is located within the RM5 units whereas the 3.2(2) )D/f.u. belongs to the RM2 units. For the PuNi3 type structure of (La0.67Mg0.33Ni2.5Co0.5)D4.0, the total isotropic lattice expansions of the a-axis and c-axis are δa/a＝7.1% and δc/c=9.1%, respectively. A significant anisotropic volume expansion (δc/c=15.8%, δV/VRM2=32.8%) is found inside the RM2 unit, but inside the RM5 unit, the volumetric expansions are 2.4% (δc/c) and 17.5% (δV/VRM5)