Structure and Hydrogen Bonding in CaSiD1+ x: Issues About Covalent Bonding

We report here our high-resolution neutron powder diffraction and neutron vibrational spectroscopy study of CaSiD1+x along with first-principles calculations, which reveal the deuterium structural arrangements and bonding in this novel alloy hydride. Both the structural and spectroscopic results show that, for x > 0, D atoms start occupying a Ca3Si interstitial site. The corresponding Si-D bond length is determined to be 1.82 Å, fully 0.24 Å larger than predicted by theory. Thus, our neutron measurements are at odds with the strongly covalent Si-H bonding in CaSiH1+x that such calculations suggest, a result which may have implications for a number of ongoing studies of metal-hydrogen systems destabilized by Si alloying. Disciplines Engineering | Materials Science and Engineering Comments Suggested Citation: Wu, H., Zhou, W. Udovic, T.J., Rush, J.J. and Yildirim, T. (2006). Structure and hydrogen bonding in CaSiD1+x: Issues about covalent bonding. Physical Review B 74, 224101. © 2006 American Physical Society http://dx.doi.org/10.1103/PhysREvB.74.224101 This journal article is available at ScholarlyCommons: http://repository.upenn.edu/mse_papers/207 Structure and hydrogen bonding in CaSiD1+x: Issues about covalent bonding H. Wu,1,2,* W. Zhou,1,3 T. J. Udovic,1 J. J. Rush,1,2 and T. Yildirim1,3 1NIST Center for Neutron Research, National Institute of Standards and Technology, 100 Bureau Drive, MS 8562, Gaithersburg, Maryland 20899-8562, USA 2Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742-2115, USA 3Department of Materials Science and Engineering, University of Pennsylvania, 3231 Walnut Street, Philadelphia, Pennsylvania 19104-6272, USA Received 11 July 2006; revised manuscript received 4 September 2006; published 7 December 2006 We report here our high-resolution neutron powder diffraction and neutron vibrational spectroscopy study of CaSiD1+x along with first-principles calculations, which reveal the deuterium structural arrangements and bonding in this novel alloy hydride. Both the structural and spectroscopic results show that, for x 0, D atoms start occupying a Ca3Si interstitial site. The corresponding Si-D bond length is determined to be 1.82 Å, fully 0.24 Å larger than predicted by theory. Thus, our neutron measurements are at odds with the strongly covalent Si-H bonding in CaSiH1+x that such calculations suggest, a result which may have implications for a number of ongoing studies of metal-hydrogen systems destabilized by Si alloying. DOI: 10.1103/PhysRevB.74.224101 PACS number s : 61.12. q, 63.20. e, 71.15.Mb, 81.05.Je