Fig. 1: Transformation and phase diagrams of sulfur.

a The low-density (LDL) and high-density liquid (HDL) sulfur are drawn in different shades of orange, and the dashed curve in the liquid LDL region denotes the transition between the liquid, made of pure rings, and LDL (lambda transition). The phase diagram shows five known solid phases (orthorhombic α-S₈ (S-I), monoclinic β-S₈, trigonal (S-II), tetragonal (S-III), rhombohedral S₆ (Rh, S-IV). The melting curve and phase boundaries are from refs. ^6,8. b The rapid compression of liquid sulfur to effectively break the ring structures and form an elemental sulfur glass of pure chain molecules (Am-S_P). Liquid sulfur before the lambda transition and its supercooled product consists purely of S₈ rings (Am-S_R, indicated by the blue arrow). The solid orange arrows represent five pathways for preparing Am-S_P by rapidly compressing the liquid (or supercooled liquid) sulfur at 300, 403, 423, 453, and 573 K. The red and blue double line arrows indicate isobaric variable-temperature experiments of Am-S_P at 5 GPa, with temperatures ranging from 5 to 573 K. The orange double-line arrow represents the compression of Am-S_P from 5 to 25.5 GPa at room temperature. Sulfur remains stable across all three pathways. The chains in Am-S_P partially convert to rings when the pressure drops below 3 GPa, as indicated by the orange dashed line marking this transition pressure. The light red area indicates the (meta)stable region of Am-S_P, which largely coincides with the P–T domain of the crystalline S-I phase. Δ denotes the experimental data points.