Figure 1
From: Natural arsenic with a unique order structure: potential for new quantum materials
(a) Crystal structure of Pnm21-type arsenic (pararsenolamprite) projected on (001) and (010). Each rectangle indicates the unit cell. (b) Comparison of crystal structures among crystalline arsenic phases. The structure of Pnm21-As consists of 1:1 rod packing of grey- and black- arsenic parts. The array represents a herringbone pattern of two pieces. Grey arsenic (\(R\bar{{3}}m\)-As) has a layer structure and can be obtained by a Peiers-type distortion along [111] direction of a simple cubic structure32,33. In the structure, the six nearest neighbours in the original simple cubic structure splits into three equidistant nearest neighbours and three next nearest neighbours. Layered atoms form six-membered rings in chair conformation with intralayer and interlayer bond distances. The atomic arrangement in black arsenic (Bmab-As) consists of puckered layers stacked in the c-direction13.
