Two-Dimensional and Three-Dimensional Tetrel-Arsenide Frameworks Templated by Li and Cs Cations

Two
new ternary tetrel pnictide phases, Li1.08Ge4.92As7 and Cs0.11Zn0.05Si0.95As, have been synthesized. Both compounds crystallize in
new structure types, which demonstrate the flexibility of Ge­(Si)–As
layers when accommodating electropositive cations of various sizes.
Li1.08Ge4.92As7 displays a Ge-As
layer motif that has not been observed in ternary Ge-As systems, while
Cs0.11Zn0.05Si0.95As exhibits a 3D
framework composed of fragments of the 2D parent-phase SiAs. For Li1.08Ge4.92As7, a combination of computational
modeling and solid-state 7Li MAS NMR was used to establish
the correct crystal structure with one mixed occupied Ge/Li site.
The compositions of the phases were confirmed through energy-dispersive
X-ray spectroscopy. Transport properties and UV–Vis spectroscopy
reveal both reported compounds to be semiconductors. Cs0.11Zn0.05Si0.95As shows high thermal stability
with congruent melting at 1300 K and an exceptionally low thermal
conductivity of 0.5 W m–1 K–1 at
300 K. Temperature-dependent Li-ion hopping dynamics in Li1.08Ge4.92As7 was characterized using 7Li solid-state NMR.

本研究成功合成两种新型三元碳族-氮族化合物相：Li₁.₀₈Ge₄.₉₂As₇与Cs₀.₁₁Zn₀.₀₅Si₀.₉₅As。两种化合物均结晶于全新结构类型，展现出锗（硅）-砷层在适配不同尺寸正电性阳离子时的结构柔性。Li₁.₀₈Ge₄.₉₂As₇具有一种此前未在三元锗-砷体系中被观测到的锗-砷层结构基元，而Cs₀.₁₁Zn₀.₀₅Si₀.₉₅As则呈现出由二维母体相SiAs片段构成的三维框架结构。针对Li₁.₀₈Ge₄.₉₂As₇，本研究结合计算建模与固态⁷Li魔角旋转核磁共振（MAS NMR）技术，确定了包含一个混合占位锗/锂位点的正确晶体结构。通过能量色散X射线能谱验证了上述物相的化学计量组成。输运性能测试与紫外-可见分光光度分析结果表明，两种目标化合物均为半导体材料。Cs₀.₁₁Zn₀.₀₅Si₀.₉₅As展现出优异的热稳定性，其在1300 K下发生一致熔融，且在300 K时的热导率极低，仅为0.5 W·m⁻¹·K⁻¹。本研究利用固态⁷Li核磁共振技术，表征了Li₁.₀₈Ge₄.₉₂As₇中随温度变化的锂离子跳跃动力学行为。