Quartzlike Carbon Dioxide: An Optically Nonlinear Extended Solid at High Pressures and Temperatures

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Abstract
An extended-solid phase, carbon dioxide phase V (CO 2 -V), was synthesized in a diamond anvil cell by laser heating the molecular orthorhombic phase, carbon dioxide phase III, above 40 gigapascals and 1800 kelvin. This new material can be quenched to ambient temperature above 1 gigapascal. The vibration spectrum of CO 2 -V is similar to that of the quartz polymorph of silicon dioxide, indicating that it is an extended covalent solid with carbon-oxygen single bonds. This material is also optically nonlinear, generating the second harmonic of a neodymium–yttrium-lithium-fluoride laser at a wavelength of 527 nanometers with a conversion efficiency that is near 0.1 percent.