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Title: Six-fold Coordinated Carbon Dioxide VI

Abstract

Under standard conditions, carbon dioxide (CO{sub 2}) is a simple molecular gas and an important atmospheric constituent while silicon dioxide (SiO{sub 2}) is a covalent solid, and represents one of the fundamental minerals of the planet. The remarkable dissimilarity between these two group IV oxides is diminished at higher pressures and temperatures as CO{sub 2} transforms to a series of solid phases, from simple molecular to a fully covalent extended-solid V, structurally analogous to SiO{sub 2} tridymite. Here, we present the discovery of a new extended-solid phase of carbon dioxide (CO{sub 2}): a six-fold coordinated stishovite-like phase VI, obtained by isothermal compression of associated CO{sub 2}-II above 50GPa at 530-650K. Together with the previously reported CO{sub 2}-V and a-carbonia, this new extended phase indicates a fundamental similarity between CO{sub 2}--a prototypical molecular solid, and SiO{sub 2}--one of Earth's fundamental building blocks. The phase diagram suggests a limited stability domain for molecular CO{sub 2}-I, and proposes that the conversion to extended-network solids above 40-50 GPa occurs via intermediate phases II, III, and IV. The crystal structure of phase VI suggests strong disorder along the caxis in stishovite-like P4{sub 2}/mnm, with carbon atoms manifesting an average six-fold coordination within the framework ofmore » sp{sup 3} hybridization.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
899112
Report Number(s):
UCRL-JRNL-220097
TRN: US200706%%497
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Journal Article
Resource Relation:
Journal Name: Nature Materials, vol. 6, no. 1, January 3, 2007, pp. 34-38
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ATOMS; CARBON; CARBON DIOXIDE; COMPRESSION; CRYSTAL STRUCTURE; HYBRIDIZATION; OXIDES; PHASE DIAGRAMS; SILICON; STABILITY

Citation Formats

Iota, V, Yoo, C, Klepeis, J, and Jenei, Z. Six-fold Coordinated Carbon Dioxide VI. United States: N. p., 2006. Web.
Iota, V, Yoo, C, Klepeis, J, & Jenei, Z. Six-fold Coordinated Carbon Dioxide VI. United States.
Iota, V, Yoo, C, Klepeis, J, and Jenei, Z. Wed . "Six-fold Coordinated Carbon Dioxide VI". United States. doi:. https://www.osti.gov/servlets/purl/899112.
@article{osti_899112,
title = {Six-fold Coordinated Carbon Dioxide VI},
author = {Iota, V and Yoo, C and Klepeis, J and Jenei, Z},
abstractNote = {Under standard conditions, carbon dioxide (CO{sub 2}) is a simple molecular gas and an important atmospheric constituent while silicon dioxide (SiO{sub 2}) is a covalent solid, and represents one of the fundamental minerals of the planet. The remarkable dissimilarity between these two group IV oxides is diminished at higher pressures and temperatures as CO{sub 2} transforms to a series of solid phases, from simple molecular to a fully covalent extended-solid V, structurally analogous to SiO{sub 2} tridymite. Here, we present the discovery of a new extended-solid phase of carbon dioxide (CO{sub 2}): a six-fold coordinated stishovite-like phase VI, obtained by isothermal compression of associated CO{sub 2}-II above 50GPa at 530-650K. Together with the previously reported CO{sub 2}-V and a-carbonia, this new extended phase indicates a fundamental similarity between CO{sub 2}--a prototypical molecular solid, and SiO{sub 2}--one of Earth's fundamental building blocks. The phase diagram suggests a limited stability domain for molecular CO{sub 2}-I, and proposes that the conversion to extended-network solids above 40-50 GPa occurs via intermediate phases II, III, and IV. The crystal structure of phase VI suggests strong disorder along the caxis in stishovite-like P4{sub 2}/mnm, with carbon atoms manifesting an average six-fold coordination within the framework of sp{sup 3} hybridization.},
doi = {},
journal = {Nature Materials, vol. 6, no. 1, January 3, 2007, pp. 34-38},
number = ,
volume = ,
place = {United States},
year = {Wed Mar 01 00:00:00 EST 2006},
month = {Wed Mar 01 00:00:00 EST 2006}
}
  • Under standard conditions, carbon dioxide (CO{sub 2}) is a simple molecular gas and an important atmospheric constituent, whereas silicon dioxide (SiO{sub 2}) is a covalent solid, and one of the fundamental minerals of the planet. The remarkable dissimilarity between these two group IV oxides is diminished at higher pressures and temperatures as CO{sub 2} transforms to a series of solid phases, from simple molecular to a fully covalent extended-solid V, structurally analogous to SiO{sub 2} tridymite. Here, we present the discovery of an extended-solid phase of CO{sub 2}: a six-fold coordinated stishovite-like phase VI, obtained by isothermal compression of associatedmore » CO{sub 2}-II above 50 GPa at 530-650 K. Together with the previously reported CO{sub 2}-V and a-carbonia, this extended phase indicates a fundamental similarity between CO{sub 2} (a prototypical molecular solid) and SiO{sub 2} (one of Earth's fundamental building blocks). We present a phase diagram with a limited stability domain for molecular CO{sub 2}-I, and suggest that the conversion to extended-network solids above 40-50 GPa occurs via intermediate phases II, III and IV. The crystal structure of phase VI suggests strong disorder along the c axis in stishovite-like P4{sub 2}/mnm, with carbon atoms manifesting an average six-fold coordination within the framework of sp{sup 3} hybridization.« less
  • In this LDRD, we examined in detail the pressure-induced bonding and local coordination changes leading to the molecular {yields} associated {yields} extended-solid transitions in carbon dioxide (CO{sub 2}). We studied the progressive delocalization of electrons from the C=O molecular double bond at high pressures and temperatures, and determined the phase stability and physical properties of a new extended-solid CO{sub 2} phase (VI). We find that the new CO{sub 2} phase VI is based on a network of six-fold coordinated (octahedral) CO{sub 6} structures similar to the ultra-hard SiO{sub 2} phase stishovite.
  • No abstract prepared.
  • The local structure of sixfold oxygen coordinated silicon ({sup [6]}Si) in sodium phosphosilicate glasses has been investigated using MAS NMR spectroscopy and ab initio quantum-chemical techniques. It has been demonstrated that {sup [6]}Si is interconnected by six PO{sub 4} tetrahedral units by sharing only their corners, forming a nearly regular [SiO{sub 6/2}]{sup 2-} octahedral site. Alkali cations behave as charge compensators of the doubly charged {sup [6]}Si species and hence play an indispensable role in stabilizing the peculiar octahedral coordination in the glasses.
  • A considerable number of optical devices have significantly benefited from the development of phosphate glasses as substrate materials. Introducing silica into sodium phosphate is an effective method to enhance its mechanical and optical properties. Through annealing treatment, the tetrahedral silicon oxide network structure (Si{sup (4)}) can be transformed into an octahedral structure (Si{sup (6)}) with more constraints. Here, we use high-temperature Raman and Nuclear Magnetic Resonance to reveal the mechanism of transformation between the Si{sup (4)} and Si{sup (6)} silicon oxide structures. The increase of the Si{sup (6)} content results in the phosphate glasses having higher refractive index and hardness.more » Based on this, the refractive index contribution of SiO{sub 6} is obtained.« less