Hydriding and dehydriding transitions in bulk and nanocrystalline binary metal hydrides were studied using the Pd-H model system by measuring pressure-composition isotherms with in situ x-ray diffractometry. Nanocrystalline Pd showed a smaller pressure hysteresis, solvus hysteresis, and hysteresis in lattice parameter, compared to bulk Pd. The time-dependence of pressure equilibration was measured after dosing with aliquots of hydrogen, giving equilibration times that were much faster in the single-phase regions than in the two-phase plateaus. In the broad two-phase plateaus, the pressure relaxations were exponential functions of time. An explanation of hysteresis is developed that is based on a dissipative potential barrier that impedes the motion of the interface due to interactions between lattice defects and the two-phase interface. The exponential pressure relaxations and hysteresis are consistent for this mechanism. For a simple model of the pinning potential, the potential barrier maximum is an order of magnitude less than typical grain boundary energies. These pinning effects are substantially different in the nanocrystalline Pd, suggesting differences in the hydriding mechanism.

中文翻译：

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界面钉扎导致二元金属氢化物中氢化物转变的滞后现象

使用Pd-H模型系统，通过原位测量压力组成等温线，研究了本体和纳米晶二元金属氢化物的氢化和脱水转变X射线衍射。与块状钯相比，纳米晶钯显示出较小的压力滞后，固溶滞后和晶格参数滞后。在加入氢气等分试样后测量压力平衡的时间依赖性，得出单相区域的平衡时间比两相高原的平衡时间快得多。在广阔的两相高原，压力松弛是时间的指数函数。磁滞现象的解释是基于耗散势垒，该势垒由于晶格缺陷和两相界面之间的相互作用而阻碍了界面的运动。指数压力松弛和滞后作用对于该机理是一致的。对于固定潜力的简单模型，势垒最大值比典型的晶界能小一个数量级。这些钉扎效应在纳米晶体Pd中基本不同，表明氢化机理不同。