Crystal and Electronic Structure and Optical Properties of AE₂SiP₄ (AE = Sr, Eu, Ba) and Ba₄Si₃P₈

Abstract

Three new compounds in the AE-Si-P (AE = Sr, Eu, Ba) systems are reported. Sr 2 SiP 4 and Eu 2 SiP 4 , the first members of their respective ternary systems, are isostructural to previously reported Ba 2 SiP 4 and crystallize in the noncentrosymmetric I42d (no. 122) space group. Ba 4 Si 3 P 8 crystallizes in the new structure type, in P2 1 /c (no. 14) space group, mP-120 Pearson symbol, Wyckoff sequence e 30 . In the crystal structures of Sr 2 SiP 4 and Eu 2 SiP 4 all SiP 4 tetrahedral building blocks are connected via formation of P-P bonds forming a 242 three-dimensional framework. In the crystal structure of Ba 4 Si 3 P 8 , Si-P tetrahedral chains formed by corner-sharing, edge-sharing, and P-P bonds are surrounded by Ba cations. This results in a quasi-onedimensional structure. Electronic structure calculations and UV/Vis measurements suggest that the AE 2 SiP 4 (AE = Sr, Eu, Ba) are direct bandgap semiconductors with bandgaps of ca. 1.4 eV and have potential for thermoelectric applications. duced crystal structures are noncentrosymmetric, for example the II-IV-V 2 chalcopyrite family (II = Mg, Zn, Cd; IV = Si, Ge, Sn; V = P, As, Sb), leading to their intensive study for nonlinear optical applications.

Ba2Si3P6: 1D Nonlinear Optical Material with Thermal Barrier Chains

“…The versatility in bonding in the polyanion results in crystal structures with different dimensionality ranging from 0D (Li8SiP4, AE4TtP4; AE = Ca, Sr, Ba; Tt = Si, Ge), 1D (K2SiP2, Ba4Si3P8, Ca3Si2P4), 2D (LiGe3As3, Li3Si7As8, Ca2Si2P4, NaGe6As6, Ba3Si4P6), and 3D (Li2SiP2, MgSiAs2, Mg3Si6As8, AE2SiP4; AE = Sr, Eu, Ba). 13,[21][22][23][24][25][26][27][28] One potential application of ternary tetrel-pnictides is infrared non-linear optical materials, where the non-centrosymmetric crystal structure is a prerequisite coupled with a suitable bandgap, high laser damage threshold, good chemical and thermal stability, and moderate mechanical properties, such as hardness. [29][30][31][32][33][34][35] This field is dominated by lateand post-transition metal chalcogenide materials.…”

“…The global aim of our work is to find materials with stronger covalent bonding between earth-abundant elements, such as Si and P. Synthesizing non-centrosymmetric phases is no straightforward task, however analysis of the reported compounds in AE-Tt-Pn systems (AE = alkaline-earth metal) reveals that a large fraction of ternary tetrel-pnictides crystallize in non-centrosymmetric structures. 21,23,24,27 We hypothesized that the repulsion of the electron-lone pairs located on pnictogen atoms is responsible for such unusually high abundance of non-centrosymmetric compounds. Typically, AE-Tt-Pn compounds are electron-balanced with bandgaps suitable for infrared applications.…”

“…Ba2Si3P6 contains distorted SiP4 tetrahedra with angles ranging from 95.7-120° (Table S4), however stronger tetrahedral distortion was reported for another 1D compound in this system, Ba4Si3P8. 23 The Si-P bonds in Ba2Si3P6 range from 2.210(2)-2.309(2) Å (Table S3), typical of Si-P bonds. [22][23][24]26,28,[40][41][42] Similarly, the P-P interatomic distance of 2.200(2) Å is typical for single covalent P-P bonds.…”

“…23 The Si-P bonds in Ba2Si3P6 range from 2.210(2)-2.309(2) Å (Table S3), typical of Si-P bonds. [22][23][24]26,28,[40][41][42] Similarly, the P-P interatomic distance of 2.200(2) Å is typical for single covalent P-P bonds. 23,[43][44][45][46] Assuming a coordination sphere of 3.5 Å, the Ba atoms are six or eight-coordinated with P, with Ba-P distances of 3.19-3.48 Å, which are in good agreement with other reported binary and ternary Ba phosphides.…”

Polymorphism of Ba2SiP4

“…The possibility of the formation of homonuclear phosphorus bonding distinguishes the family of phosphidosilicates from the oxido‐ and nitridosilicates. Isolated P–P bonding was described in AlSiP 3 , Ca 3 Si 8 P 14 , Ba 2 Si 3 P 6 and Ba 4 Si 3 P 8 , for example, whereas in LaSi 2 P 6 up to four different polyphosphide anions (P n ) –( n +2) with n = 3–6 and in Li 3 Si 3 P 7 [4a] polyphosphide chains exist. Tetragonal Ba 2 SiP 4 ‐ tI 28 is the first example where all SiP 4 tetrahedra are connected by P–P bonds.…”