Proton NMR studies of hydrogen diffusion and electronic structure in crystalline and amorphous titanium-copper hydrides
Proton NMR studies of hydrogen diffusion and electronic structure in crystalline and amorphous titanium-copper hydrides
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DOI：
10.1103/physrevb.26.6362
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发表时间：
1982-12
影响因子：
3.7
通讯作者：
R. C. Bowman;A. Maeland;W. Rhim
中科院分区：
文献类型：
--
作者：
R. C. Bowman;A. Maeland;W. Rhim
已在结晶TiCu H 0.94、Ti 2 Cu H 1.9 和Ti 2 Cu H 2.63 以及非晶a-TiCu H 1.4 中测量了质子线形状、自旋晶格和旋转坐标系弛豫时间以及Knight 位移。刚性晶格线形状的二阶矩表明，质子占据了晶体TiCu H 0.94 和Ti 2 Cu H 1.9 中的Ti 4 间隙位点，而Ti 4 和Ti 4 Cu 2 位点都占据了晶体Ti 2 Cu H 2.63 中。尽管不可能详细测定非晶a-TiCu H 1.4 中的氢位点占据，但质子二阶矩意味着除了四面体位点占据之外还存在八面体位点占据。主体金属结构和氢位点占据强烈影响氢扩散行为和电子特性。质子超精细相互作用似乎由费米能级附近 Ti d 态的转移核心极化项主导，正如之前在 γ 相 Ti H x 和其他 Ti 基三元氢化物中发现的那样。与晶体样品的密度相比，在非晶a-TiCu H 1.4 中在质子位点监测到的费米能级电子态密度明显降低。有人认为，这种减少可能反映了由于非晶相中长程有序的消除而导致的能带模糊。对于非晶a-TiCu H 1.3±0.1 已证实氢扩散大大增强（相对于晶态TiCu H 0.94 和γ− Ti H x ）。晶体Ti 2 Cu H x 中的扩散行为支持这样的观点：通过八面体位点的H原子扩散跳跃具有比直接四面体到四面体跳跃路径更低的活化能。
The proton line shapes, spin-lattice and rotating-frame relaxation times, and Knight shifts have been measured in crystalline TiCu H 0.94, Ti 2 Cu H 1.9, and Ti 2 Cu H 2.63, and in amorphous a-TiCu H 1.4. The second moments of the rigid-lattice line shapes indicate that protons occupy Ti 4 interstitial sites in crystalline TiCu H 0.94 and Ti 2 Cu H 1.9 while both Ti 4 and Ti 4 Cu 2 sites are occupied in crystalline Ti 2 Cu H 2.63. Although a detailed determination of hydrogen site occupancy in amorphous a-TiCu H 1.4 was not possible, the proton second moment implies octahedral site occupancy in addition to tetrahedral site occupancy. The host-metal structure and hydrogen site occupancies strongly influence both the hydrogen-diffusion behavior and electronic properties. The proton hyperfine interactions appear to be dominated by the transferred core-polarization terms from the Ti d states near the Fermi level as previously found in γ-phase Ti H x and other Ti-based ternary hydrides. The density of electron states at the Fermi level as monitored at the proton sites is apparently reduced in amorphous a-TiCu H 1.4 when compared with densities for the crystalline samples. It is suggested that this reduction may reflect a smearing of the energy bands with the elimination of long-range order in the amorphous phase. The greatly enhanced hydrogen diffusion (relative to crystalline TiCu H 0.94 and γ− Ti H x) has been confirmed for amorphous a-TiCu H 1.3±0.1. The diffusion behavior in crystalline Ti 2 Cu H x supports the view that H-atom diffusion jumps through octahedral sites have lower activation energies than the direct tetrahedral-to-tetrahedral jump paths.