Hydrogenation-Induced Structure and Property Changes in the Rare-Earth Metal Gallide NdGa: Evolution of a [GaH]2– Polyanion Containing Peierls-like Ga–H Chains

详细信息    查看全文

• 作者：Jonas ?ngstr?m ; Robert Johansson ; Tapati Sarkar ; Magnus H. S?rby ; Claudia Zlotea ; Mikael S. Andersson ; Per Nordblad ; Ralph H. Scheicher ; Ulrich H?ussermann ; Martin Sahlberg
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：January 4, 2016
• 年：2016
• 卷：55
• 期：1
• 页码：345-352
• 全文大小：466K
• ISSN：1520-510X

文摘

The hydride NdGaH_1+x (x ≈ 0.66) and its deuterized analogue were obtained by sintering the Zintl phase NdGa with the CrB structure in a hydrogen atmosphere at pressures of 10?20 bar and temperatures near 300 °C. The system NdGa/NdGaH_1+x exhibits reversible H storage capability. H uptake and release were investigated by kinetic absorption measurements and thermal desorption mass spectroscopy, which showed a maximum H concentration corresponding to “NdGaH₂” (0.93 wt % H) and a two-step desorption process, respectively. The crystal structure of NdGaH_1+x was characterized by neutron diffraction (P2₁/m, a = 4.1103(7), b = 4.1662(7), c = 6.464(1) ?, β = 108.61(1)° Z = 2). H incorporates in NdGa by occupying two distinct positions, H1 and H2. H1 is coordinated in a tetrahedral fashion by Nd atoms. The H2 position displays flexible occupancy, and H2 atoms attain a trigonal bipyramidal coordination by centering a triangle of Nd atoms and bridging two Ga atoms. The phase stability and electronic structure of NdGaH_1+x were analyzed by first-principles DFT calculations. NdGaH1H2 (NdGaH₂) may be expressed as Nd³⁺(H1^–)[GaH2]^2–. The two-dimensional polyanion [GaH]^2– features linear ?H–Ga–H–Ga– chains with alternating short (1.8 ?) and long (2.4 ?) Ga–H distances, which resembles a Peierls distortion. H2 deficiency (x < 1) results in the fragmentation of chains. For x = 0.66 arrangements with five-atom moieties, Ga–H–Ga–H–Ga are energetically most favorable. From magnetic measurements, the Curie–Weiss constant and effective magnetic moment of NdGaH_1.66 were obtained. The former indicates antiferromagnetic interactions, and the latter attains a value of ～3.6 μ_B, which is typical for compounds containing Nd³⁺ ions.