High-pressure Synthesis of Strontium Hexasilicide

Abstract

The binary phase SrSi 6 was prepared at a pressure of 10(1) GPa and a temperature of 1520(150) K. Single crystal refinements and powder diffraction data reveal that the compound crystallizes in the orthorhombic crystal system (Cmcm, a = 4.4692(4), b = 10.256(1), c = 11.698(1)Å) and is isopointal to EuGa 2 Ge 4 and EuSi 6 . Exothermic decomposition of the compound into SrSi 2 and Si at 797 K and ambient pressure indicates that the compound is a metastable high-pressure phase. Analysis of the chemical bonding using the electron localization function and calculated charge densities reveals covalent bonding within the polyanion of four-bonded silicon atoms. Strontium cations are enclosed in the 3D net resulting in an electron balance Sr 2+ [Si 0 ] 2− 6 . In the electronic density of states the excess electrons of the framework are assigned to a filling of antibonding bands. SrSi 6 is a metallic conductor with an electrical resistivity of ρ ≈ 250 µΩ·cm at 300 K. Magnetization measurements indicate diamagnetic behaviour (χ 0 = −50 · 10 −6 emu·mol −1 ).

High-pressure synthesis of the electron-excess compound CaSi6

“…Atomic coordinates and displacement parameters are summarized in Table 2, and interatomic distances in Table 3. The atomic arrangement is isopointal to EuGa 2 Ge 4 [5] and isotypic to EuSi 6 [7], SrSi 6 [8] and BaSi 6 [9,10]. A 3D network of four-bonded Si atoms encloses large voids, which are occupied by calcium atoms (Fig.…”

“…This hints at a different kind of bonding than two-centre two-electron interactions for the four-bonded silicon atoms and it is justified to describe the bonding situation as analogous to that of SrSi 6 and EuSi 6 [7,8]. For these compounds, an analysis by means of the electron localization function reveals a transfer of the electrons of the metal to the silicon framework.…”

“…In sharp contrast, binary silicon-rich high-pressure phases like EuSi 6 [7], SrSi 6 [8] or BaSi 6 [9,10] comprise solely four-bonded silicon atoms. The metal-type temperature dependence of the electrical conductivity is in agreement with a description as Eu[(4b)Si 0 ] 6 Á 2e À .…”

Refinement of the crystal structure of barium hexasilicide, BaSi6

“…Crystal structure data based on aRietveld refinement were published independently by Yamanaka et al [3]. The crystal structure is isotypic to the binary compounds MSi 6 (M =Eu [4]; Ca [5], Sr [6]) and isopointal to ternary EuGa 2 Ge 4 [7]. The atomic arrangement consists of a3Dnetwork formed by four-bonded silicon atoms with large voids being occupied by barium atoms.…”

High‐pressure High‐temperature Synthesis, Magnetic Properties and X‐ray Absorption Spectroscopy of Phases RE3Sn7 and hp‐RESn3–x (RE = Tb, Ho, Er)

“…In the context of recent high-pressure high-temperature syntheses of new binary silicon-and germanium-rich intermetallic compounds [1][2][3][4][5][6][7][8][9][10][11], the tin-rich parts of the phase diagrams RE−Sn (RE = Tb, Ho, Er) were reinvestigated. An earlier study reports on the formation of cubic close packed Cu 3 Au-type phases RESn 3 (RE = Tb, Ho, Er) at high-pressure high-temperature conditions [12].…”