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DOE OSTI2023

On the Electride Nature of Na–hP4

Early quantum mechanical models suggested that pressure drives solids towards free-electron metal behavior where the ions are locked into simple close-packed structures. The prediction and subsequent discovery of high-pressure electrides (HPEs), compounds assuming open structures where the valence electrons are localized in interstitial voids, required a paradigm shift. Our quantum chemical calculations on the iconic insulating Na-hP4 HPE show that increasing density causes a 3s→3pd electronic transition due to Pauli repulsion between the 1s2s and 3s states, and orthogonality of the 3pd states to the core. The large lobes of the resulting Na-pd hybrid orbitals point towards the center of an 11-membered penta-capped trigonal prism and overlap constructively, forming multicentered bonds, which are responsible for the emergence of the interstitial charge localization in Na-hP4. As a result, these multicentered bonds facilitate the increased density of this phase, which is key for its stabilization under pressure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

Materials Data on NaPd3 by Materials Project

NaPd3 is Uranium Silicide-like structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Na is bonded to twelve Pd atoms to form a mixture of face, edge, and corner-sharing NaPd12 cuboctahedra. There are four shorter (2.84 Å) and eight longer (2.85 Å) Na–Pd bond lengths. There are two inequivalent Pd sites. In the first Pd site, Pd is bonded to four equivalent Na atoms to form a mixture of distorted edge and corner-sharing PdNa4 cuboctahedra. In the second Pd site, Pd is bonded in a distorted square co-planar geometry to four equivalent Na atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Na3Pd by Materials Project

Na3Pd is alpha bismuth trifluoride structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. there are two inequivalent Na sites. In the first Na site, Na is bonded in a 4-coordinate geometry to four equivalent Na and four equivalent Pd atoms. All Na–Na bond lengths are 3.17 Å. All Na–Pd bond lengths are 3.17 Å. In the second Na site, Na is bonded to eight equivalent Na and four equivalent Pd atoms to form NaNa8Pd4 cuboctahedra that share corners with four equivalent NaNa8Pd4 cuboctahedra, corners with eight equivalent PdNa12 cuboctahedra, edges with eight equivalent NaNa8Pd4 cuboctahedra, faces with four equivalent NaNa8Pd4 cuboctahedra, and faces with six equivalent PdNa12 cuboctahedra. All Na–Pd bond lengths are 3.36 Å. Pd is bonded to twelve Na atoms to form PdNa12 cuboctahedra that share corners with four equivalent PdNa12 cuboctahedra, corners with eight equivalent NaNa8Pd4 cuboctahedra, edges with eight equivalent PdNa12 cuboctahedra, faces with four equivalent PdNa12 cuboctahedra, and faces with six equivalent NaNa8Pd4 cuboctahedra.

36 MATERIALS SCIENCE↗