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<p>SO<sub>2</sub> is a molecule of significant industrial and geochemical importance, known for its role in sulphuric acid production and its natural occurrence in volcanic processes. Recent studies have revealed pressure-induced amorphisation and the formation of polymeric amorphous phases in SO<sub>2</sub>, behaviours analogous to those observed in other fundamental molecular systems such as CO<sub>2</sub>, N<sub>2</sub>, and CS<sub>2</sub>. Here, we identify a mixture of polymeric SO<sub>2</sub> phases, with space groups <i>A</i><i>m</i><i>a</i>2 (<i>Z</i> = 2) and <i>P</i><i>m</i><i>c</i>2<sub>1</sub> (<i>Z</i> = 8), the latter a homologue of <i>γ</i>-SeO<sub>2</sub>, as the crystalline parents of the previously reported threefold-coordinated amorphous SO<sub>2</sub> observed above 25 GPa. These phases were characterized using a combination of advanced synthesis and refined high-pressure loading techniques, alongside x-ray diffraction, Raman, and infrared spectroscopy. Structural assignments were further supported by numerical predictions of candidate crystal structures. Notably, the <i>A</i><i>m</i><i>a</i>2 and <i>γ</i>-SeO<sub>2</sub>-like phases exhibit in the pressure region 20–60 GPa the lowest and near-degenerate enthalpies, <i>A</i><i>m</i><i>a</i>2 being stable below 25 GPa and <i>γ</i>-SeO<sub>2</sub>-like above 25 GPa. Both phases feature distinctive W-shaped polymeric units, a structural motif identified long ago at ambient pressure in the rare-mineral Downeyite (SeO<sub>2</sub>), but the stacking of chains is different and pressure-dependent.</p>

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Crystalline polymeric phases of sulphur dioxide

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年11月26日

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  • Huichao Zhang,
  • Philip Dalladay-Simpson,
  • Francesco Capitani,
  • Cheng Ji,
  • Li Zhang,
  • Mario Santoro,
  • Federico A. Gorelli,
  • Roman Martoňák

摘要

SO2 is a molecule of significant industrial and geochemical importance, known for its role in sulphuric acid production and its natural occurrence in volcanic processes. Recent studies have revealed pressure-induced amorphisation and the formation of polymeric amorphous phases in SO2, behaviours analogous to those observed in other fundamental molecular systems such as CO2, N2, and CS2. Here, we identify a mixture of polymeric SO2 phases, with space groups Ama2 (Z = 2) and Pmc21 (Z = 8), the latter a homologue of γ-SeO2, as the crystalline parents of the previously reported threefold-coordinated amorphous SO2 observed above 25 GPa. These phases were characterized using a combination of advanced synthesis and refined high-pressure loading techniques, alongside x-ray diffraction, Raman, and infrared spectroscopy. Structural assignments were further supported by numerical predictions of candidate crystal structures. Notably, the Ama2 and γ-SeO2-like phases exhibit in the pressure region 20–60 GPa the lowest and near-degenerate enthalpies, Ama2 being stable below 25 GPa and γ-SeO2-like above 25 GPa. Both phases feature distinctive W-shaped polymeric units, a structural motif identified long ago at ambient pressure in the rare-mineral Downeyite (SeO2), but the stacking of chains is different and pressure-dependent.