The Influence of Boron Doping Concentration on MgH2 Electronic Structure
S. Kurkoa, B. Paskaš-Mamula b, Lj. Matović a, J. Grbović Novaković a, N. Novaković b
aUniversity of Belgrade, Vinča Institute of Nuclear Sciences, Laboratory for Material Sciences, P.O. Box 522, 11001 Belgrade, Serbia
bUniversity of Belgrade, Vinča Institute of Nuclear Sciences, Laboratory for Nuclear and Plasma Physics, P.O. Box 522, 11001 Belgrade, Serbia
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We have performed ab initio electronic structure calculations of Mg1-xBxH2 compounds with different boron concentrations, ranging from x =0.0625 to 0.5. Full structural relaxation was performed in order to properly describe influence of dopant on host matrix. Results showed that there is a strong influence of boron concentration on structural and thermodynamic stability of compound. B-H bond length is substantially shorter then in Mg-H coordination polyhedron. Boron significantly contributes to density of states at Fermi level within energy gap. The width of boron electronic states heavily depends on boron concentration, causing reduction of energy gap of host MgH2, and leading to metallic nature of compound with highest boron concentration. The predicted thermodynamic instability of compounds with higher boron concentration is in agreement with experimental findings that under similar stoichiometry, boron with magnesium forms only complex hydride, Mg(BH4)2. It is also shown that existence of stable hydrides with MgH2 rutile structure and small concentration of boron is possible in principle and that boron can be used to further destabilize MgH2 in order to enhance its hydrogen sorption-desorption kinetics.
DOI: 10.12693/APhysPolA.120.238
PACS numbers: 31.15.A-, 88.80.F-, 88.30.R-