%0 Journal Article %T Fundamental Study of Hydrogen Segregation at Vacancy and Grain Boundary in Palladium %A Hieu H. Pham %A Tahir Cagin %J Physics %D 2015 %I arXiv %X We have studied the fundamental process of hydrogen binding at interstitial, vacancy and grain boundary (GB) in palladium crystals using Density-Functional Theory. It showed that hydrogen prefers to occupy the octahedral interstitial site in Pd matrix, however a stable H-vacancy complex with most H occupations would contain up to eight hydrogen atoms surrounding the vacancy at tetrahedral sites. Furthermore, H presence assists the pairing or formation of nearby vacancies, which in agreement with previous suggestions by both experiment and theory investigation. Also, this observation could imply about a hydrogen embrittlement (HE) mechanism through the connections of microvoid and cracks. The segregation of hydrogen at grain boundary, nevertheless, has shown a different effect. High H accumulation results in grain boundary extension, which is related the HE mechanism of grain decohesion observed by experiments. %U http://arxiv.org/abs/1506.00302v1