Study on the Interaction Between Hydrogen Atoms and Metals Included in Hydrogen Storage Metals

用Siebert型压力-浓度-等温线装置测定了金属氢体系的压力-浓度-等温线（PCT）。改进了装置，增加了水平样品容器，减小了死腔。该装置的氢气泄漏率为4.82 × 10 - 4 <-4>Pa·dm^3·s^<-1>。用该装置测定LaNi_<4.5>Co_<0.5>（1-x）-H_2O系PCT图，其重现性良好。测得LaNi_ Co_ -H_6的焓变（ΔH）和熵变（ΔS）<4.5>分别<0.5>为-32.7 kJ mol（H_2）^<-1>和113 J mol（H_2）^<-1>K^<-1><0.2>。P6/mmm）和LaNi_5H_6（β相; P31 m）的氢与金属的相互作用。发现在α相和β相中，氢原子与Ni（1）原子形成较强的化学键，而与La原子形成较强的化学键。这些结果与La和Ni的键生成热的预测不雅阁，LaNi_Co_3中<4.5>，<0.5>Ni-Co键级的变化比Ni-Ni键级的变化强。这一发现与LaNi_5比LaNi_Co_3更易失效的实验结果相一致<4.5><0.5>。金属与氢原子之间的相互作用似乎受到团簇大小的影响。本研究中使用的是小团簇模型（HNi_<13>La），对于比本研究中使用的更大的团簇模型，有必要研究其电子结构。

The Siebert-type apparatus was made to measure pressure-concentration-isotherm (PCT) diagrams of metal hydrogen systems. The apparatus equipped with a horizontal sample container, was improved to minimize the dead space. A leak rate of the hydrogen of the apparatus was 4.82 x 10^<-4> Pa dm^3 s^<-1>. When PCT diagrams of LaNi_<4.5>Co_<0.5> - hydrogen systems were measured using this apparatus, the reproducibility of the diagram was invariably good. The enthalpy change (ΔH) and entropy change (ΔS) determined for LaNi_<4.5>Co_<0.5> -H_6 were -32.7 kJ mol(H_2)^<-1> and 113 J mol (H_2)^<-1> K^<-1>, respectively.The electronic structures of LaNi_5 , LaNi_5H_<0.2> (α phase ; P6/mmm) and LaNi_5H_6 (β phase ; P31m) were investigated by means of the DV-X α cluster method to understand the interaction between hydrogen and metals. It is found that the hydrogen atoms make a strong chemical bond with Ni (1) atoms rather than La atoms in both the phases of α and β. These results were not accord with the expectation from the heat of formations of the hydrides of La and Ni.In the case of LaNi_<4.5>Co_<0.5>, the bond order of Ni - Co changed somewhat stronger than that of Ni - Ni. This finding is consistent with the experimental results that LaNi_5 fails easily than LaNi_<4.5>Co_<0.5> by repetition of the procedure of the hydrogen absorption and desorption. The interaction between the metals and hydrogen atoms seems to be affected by the cluster size. The small cluster model (HNi_<13>La) was used in this study, it is necessary to study the electronic structures for larger cluster models than that used in this study.