Electronic Structures of KNa<sub>3</sub>In<sub>9</sub> and Na<sub>2</sub>In, Two Metallic Phases with Classical Closed-Shell Electronic Configurations

2006-04-03T00:00:00Z (GMT) by Bin Li John D. Corbett
The cluster compounds KNa<sub>3</sub>In<sub>9</sub> [K<sub>2</sub>Na<sub>6</sub>(In<sub>12</sub>)(In)<sub>6</sub>] and Na<sub>2</sub>In [(Na)<sub>8</sub>(In<sub>4</sub>)], which contain In<sub>12</sub> icosahedra interbridged by 4-bonded In atoms and isolated In<sub>4</sub> tetrahedra, respectively, both have classical closed-shell electronic configurations but show metallic transport properties. These contrasts have been studied by means of first-principles density functional methods (LMTO-ASA). Several bands cross the Fermi level in both compounds, consistent with their metallic properties. In KNa<sub>3</sub>In<sub>9</sub>, the metal atom framework alone is sufficient to generate a metallic characteristic. The alkali-metal s and indium p orbitals mix considerably in both phases, providing for substantial covalent contributions to their stabilities as well as bands crossing <i>E</i><sub>f</sub>. The participation of Na atoms in the 3D bonding networks is more striking in cation-richer Na<sub>2</sub>In than in KNa<sub>3</sub>In<sub>9</sub>.