Netzwerke aus Supertetraedern und Lithiumionenbeweglichkeit in Li₂SiP₂ und LiSi₂P₃

Abstract

Die neuen Phosphidosilicate Li2SiP2 und LiSi2P3 wurden aus den Elementen bei 1123 K synthetisiert und durch Einkristallstrukturanalyse charakterisiert. Li2SiP2 (I41/acd, Z=32, a=12.111(1) Å, c=18.658(2) Å) enthält zwei sich durchdringende Diamant‐analoge Tetraedernetzwerke aus eckenverknüpften T2‐Supertetraedern [(SiP4/2)4]. In der komplexen Struktur von LiSi2P3 (I41/a, Z=100, a=18.4757(3) Å, c=35.0982(6) Å) liegen Sphalerit‐analoge sich durchdringende Netzwerke aus T4‐ und T5‐Supertetraedern mit je einer gemeinsamen SiP4‐Gruppe vor. Lithium ist in den Zwischenräumen der Supertetraeder durch vier bis sechs Phosphoratome koordiniert. Temperaturabhängige 7Li‐MAS‐NMR‐Spektren deuten auf eine hohe Beweglichkeit der Li+‐Ionen mit geringen Aktivierungsenergien von 0.1 eV für Li2SiP2 und 0.07 eV für LiSi2P3.

Fast Sodium‐Ion Conductivity in Supertetrahedral Phosphidosilicates

“…TheT 5s upertetrahedra in LT-NaSi 2 P 3 and HT-NaSi 2 P 3 lack one Si atom in their centers.This was already observed in other T5 compounds,namely [In 34 S 54 ], 6À [27] LiSi 2 P 3 [11] and HP-B 2 S 3 . [28] Thei nfinite connection of SiP 4 supertetrahedra formally gives SiP with sphalerite-type structure.A ssuming Si 4+ and P 3À ions,SiP is not electroneutral and Si vacancies are required, leading to Si 3 P 4 ,which is unknown.…”

“…Examples are ZnI 2 , [6] Li 2 SiN 2 (T2), [7] Na 6 B 10 S 18 (T3), [8] and Ca 18.75 Li 10.5 [Al 39 N 55 ]:Eu 2+ (T5). [9] These interpenetrating supertetrahedral networks do not exhibit large pores,b ut their topology enforces an inhomogeneous distribution of the cations by confining them into the spaces between the large clusters.This introduces limitations to the coordination of the cations,w hich may be weaker bonded in more irregular surroundings by the anions of the cluster surfaces.T hus, supertetrahedral anionic networks potentially favor the mobility of the cations and are therefore candidates for fast ion conductivity.The recently reported Li + -ion mobility in the phosphidosilicates Li 2 SiP 2 [10] and LiSi 2 P 3 [11] with supertetrahedral networks based on SiP 4 entities supports this concept.…”

Li7Cd4.5Ge4Se16 and Li6.4Cd4.8Sn4Se16: Strong Nonlinear Optical Response in Quaternary Diamond‐Like Selenide Networks

“…As shown in Figure 2A, all CdSe 4 and MSe 4 tetrahedra are polarized in the same direction, c. These polar arrangements are responsible for the large SHG responses observed. In addition, Li 6 16 revealed the larger contribution of the heavier and more polarizablec enter cations to the NLO property.Moreover,t he congruent melting behavior at rather low temperatures is extremelyb eneficial to the growth of bulk crystal. These two compounds, with their interesting structures and properties, may arousef urther interest in the exploration of new chalcogenides with diamond-like structures.…”

“…IR nonlinear optical (NLO) crystals are key materials to realize the output of such lasers through the frequency conversion of near-IR (NIR) lasers. [1][2][3][4][5][6][7][8][9][10] However, the traditionalc halcopyrite-type IR NLO crystals( e.g.,A gGaQ 2 (Q = S, Se) [11] and ZnGeP 2 [12] )s uffer from drawbacks that severely limit their wider application, such as a low laser damage threshold or two-photon absorption (TPA). Thus, the exploration and development of new high-performance IR NLO compoundsi so fb road scientific and technological importance.…”

Aliovalent substitution in phosphide‐based materials – Crystal structures of Na10AlTaP6 and Na3GaP2 featuring edge‐sharing EP4 tetrahedra (E=Al/Ta and Ga)

“…By reducing the amount of lithium in phosphidotetrelates many different structures with condensed and covalently connected tetrahedra are observed. Illustrative examples of this manifold structural variety are Li 10 Si 2 P 6 , which features edgesharing SiP 4 double tetrahedra, [6] Li 2 SiP 2 /Li 2 GeP 2 and LiSi 2 P 3 , [7][8][9] where SiP 4 and GeP 4 tetrahedra are condensed to a network of super-tetrahedra, Li 3 Si 3 P 7 with double layers formed by vertexsharing SiP 4 tetrahedra, [6] and LiGe 3 P 3 with a two-dimensional polyanion comprising GeP 4 and Ge(P 3 Ge) tetrahedra. [8] A formally aliovalent substitution of the tetrel by a triel element leads to the lithium phosphidotrielates Li 3 AlP 2 and Li 3 GaP 2 which contain two-dimensional layers of corner-and edge-sharing tetrahedra, [4,10] whereas the corresponding Li 3 InP 2 shows a polyanionic framework of corner-sharing InP 4 supertetrahedra.…”