The metallic zintl phase Ba3Si4 - synthesis, crystal structure, chemical bonding, and physical properties

Abstract

The Zintl phase Ba3Si4 has been synthesized from the elements at 1273 K as a single phase. No homogeneity range has been found. The compound decomposes peritectically at 1307(5) K to BaSi2 and melt. The butterfly-shaped Si-4(6-) Zintl anion in the crystal Structure of Ba3Si4 (Pearson symbol tP28, space group P4(2)/mnm, 8.5233(3) angstrom, c = 11.8322(6) angstrom) shows only slightly different Si-Si bond lengths of d(Si-Si) = 2.4183(6) angstrom (1 x) and 2.4254(3) angstrom (4x). The compound is diamagnetic with chi approximate to -50 x 10(-6) cm(3) mol(-1). DC resistivity measurements show a high electrical resistivity (rho(300 K) 1.2 x 10(-3) Omega m) with positive temperature gradient d rho/dT The temperature dependence of the isotropic signal shift and the spin-lattice relaxation times in Si-29 NMR spectroscopy confirms the metallic behavior. The experimental results are in accordance with the calculated electronic band structure. which indicates a metal with a low density of states at the Fermi level. The electron localization function (ELF) is used for analysis of chemical bonding. The reaction of solid Ba3Si4 with gaseous HCl leads to the oxidation of the Si-4(6-) Zintl anion and yields nanoporous silicon.