Transformation and structure of silicatelike CO2-V

Article

关键词: CARBON-DIOXIDE;    HIGH-PRESSURE;    CRYSTAL-STRUCTURE;    PHASE;    CRISTOBALITE;    DENSITY;   

DOI  :  10.1103/PhysRevB.87.214103

来源: SCIE

【 摘 要 】

We report the evidence of two different polymorphs for polymeric CO2-V in tridymitelike (V-TD in P2(1)2(1)2(1)) and beta-cristobalitelike (V-CR in I -42d) structures. The V-TD phase is produced by laser-heating phase III (Cmca) above 40 GPa, whereas the V-CR phase by laser-heating highly compressed phase II (P4(2)/mnm-iso-space group to stishovite) and IV (P4(1)2(1)2-iso-space group to alpha-cristobalite) above 35 GPa. The density of the V-CR (3.988 g/cm(3)) is similar to 12% larger than that of the V-TD (3.559 g/cm(3)) at 50 GPa, while the density difference reduces to similar to 4% at ambient pressure. This results in a substantially smaller bulk modulus (B-o = 127 GPa, B' = 5.6) for the V-CR phase than that of the V-TD (B-o = 270 GPa, B' = 1.9). The smaller density of the V-TD is due to the open structure of corner shared CO4 tetrahedra and a great level of distortion in C-O-C angles resulting in a highly buckled layer structure; yet, the structural relationship gives rise to the specific transition to occur depending on the initial phase, either displacively from phase IV to phase V-CR or diffusively from phase III to phase V-TD. The results also provide new constraints for the phase/chemical transformation diagram of carbon dioxide.

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