Structural diversity and electronic properties in potassium silicides

Abstract

Stable potassium silicides in the complete compositional landscape were systematically explored up to 30 GPa using the variable-composition evolutionary structure prediction method. The results show that KSi, KSi, KSi, KSi, KSi, KSi, KSi, KSi, and KSi have their stability fields in the phase diagram. The spatial dimensional diversity of polymerized silicon atoms (0D "isolated" anion, dimer, Si group, 1D zigzag chain, 2D layer, and 3D network) under the potassium sublattice was uncovered as silicon content increases. Especially, the 2D layered silicon presents interestingly a variety of shapes, such as the "4 + 6" ring, "4 + 8"ring, and 8-membered ring. K-Si bonding exhibits a mixed covalency and ionicity, while Si-Si bonding is always of covalent character. Semiconductivity or metallicity mainly depends on the form of sublattices and K:Si ratio, which allows us to find more semiconductors in the Si-rich side when closed-shell K cations are encompassed by polymerized Si. The semiconducting silicides present strong absorption in the infrared and visible light range. These findings open up the avenue for experimental synthesis of alkali metal-IVA compounds and potential applications as battery electrode materials or photoelectric materials.

Pressure-Induced Structural Phase Transition and Superconductivity in NaSn5

“…On the other hand, the dimensionality of the tin network in Na-Sn compounds has also been the focus of research. − Depending on the Na:Sn atomic ratio, the dimensionality of Sn atoms can undergo big changes, from the zero-dimensional “isolated” Sn anions to the dimeric Sn 2 units, the tetrahedral [Sn 4 ] 4– anions, the two-dimensional Sn layers, and the three-dimensional Sn network, presenting dimensional diversity. These are similar to the polymerization forms of Si atoms observed in the K-Si system and carbon atoms in the Ca-C system. − Eighteen compounds have been reported so far. ,,− Among them, P 4̅2 1 m -NaSn 5 , Pmmm -NaSn 3 , C 2/ m -NaSn 2 , P 2/ n -Na 7 Sn 12 , I 4 1 / acd -NaSn, P 6 3 / mmc -Na 9 Sn 4 , I 4̅3 d -Na 15 Sn 4 , and Pnma -Na 4 Sn have been experimentally reported. NaSn 5 is of particular interest since it has the highest tin content reported so far in the experiment.…”

“…It is similar to the polymerization forms of Si atoms observed in the K-Si system and carbon atoms in the Ca-C system. [16][17][18] Eighteen compounds have been reported so far. 13,14,[19][20][21][22][23] Among them, P-421m-NaSn5 20 , Pmmm-NaSn3 19 , C2/m-NaSn2 13 , P2/n-Na7Sn12 14 , I41/acd-NaSn 21 , P63/mmc-Na9Sn4 22 , I-43d-Na15Sn4 23 , Pnma-Na4Sn 23 have been experimentally reported.…”

Pressure-induced stable structures and physical properties of Sr–Ge system

“…Such a rich structural diversity naturally brings interesting physical phenomena and properties, which can be used in solar-cells, thermoelectricity, and optoelectronics. [1,2] For example, an excellent ZT value = 1.1 was achieved in the n-type Mg 2 (Si, Sn) system under ambient condition, and they can be seen as promising thermoelectric materials. [3] Both BaGe 2 and SrGe 2 show high optical absorption coefficients (7.5×10 4 cm −1 and 7.8×10 4 cm −1 at hω = 1.5 eV), indicating that they are ideal solar cell candidates.…”