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Using density functional theory we examine the crystal structure and thefinite-temperature thermodynamics of formation and dehydrogenation for the newquaternary hydride Li4BN3H10. Two recent studies based on X-ray and neutrondiffraction have reported three bcc crystal structures for this phase. Whilethese structures possess identical space groups and similar lattice constants,internal coordinate differences result in bond length discrepancies as large as0.2 A. Geometry optimization calculations on the experimental structures revealthat the apparent discrepancies are an artifact of X-ray interactions withstrong bond polarization; the relaxed structures are essentially identical.Regarding reaction energetics, the present calculations predict that theformation reaction 3LiNH2 + LiBH4 -> Li4BN3H10 is exothermic with enthalpyDelta H(T=300K) = -11.8 kJ/(mol f.u.), consistent with reports of spontaneousLi4BN3H10 formation in the literature. Calorimetry experiments have beenreported for the dehydrogenation reaction, but have proven difficult tointerpret. To help clarify the thermodynamics we evaluate the free energies ofseventeen candidate dehydrogenation pathways over the temperature range T =0-1000 K. At temperatures where H2 release has been experimentally observed (T\~ 520-630 K), the favored dehydrogenation reaction is Li4BN3H10 -> Li3BN2 +LiNH2 + 4 H2, which is weakly endothermic [Delta H(T=550K) = 12.8 kJ/(mol H2)].The small calculated Delta H is consistent with the unsuccessful attempts atre-hydriding reported in the literature, and suggests that the moderately hightemperatures needed for H-desorption result from slow kinetics.Comment: 9 pages, 2 figures Revised versio

physical review. b, condensed matter and materials physics

Reaction energetics and crystal structure of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mi>Li</mml:mi><mml:mn>4</mml:mn></mml:msub><mml:msub><mml:mi>BN</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">H</mml:mi><mml:mn>10</mml:mn></mml:msub></mml:mrow></mml:math>from first principles

Reaction energetics and crystal structure ofLi4BN3H10from first principles