Phase Transformations and Metallization of Magnesium Oxide at High Pressure and Temperature

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Science  22 Nov 2012:
DOI: 10.1126/science.1229450

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Magnesium oxide (MgO) is representative of the rocky materials comprising the mantles of terrestrial planets, such that its properties at high temperatures and pressures reflect the nature of planetary interiors. Shock-compression experiments on MgO to pressures of 1.4 TPa reveal a sequence of two phase transformations: (i) from B1 (NaCl) to B2 (CsCl) crystal structures above 0.36 TPa, and (ii) from electrically insulating solid to metallic liquid above 0.60 TPa. The transitions exhibit large latent heats that are likely to affect the structure and evolution of super-Earths. Together with data on other oxide liquids, we conclude that magmas deep inside terrestrial planets can be electrically conductive, enabling magnetic field–producing dynamo action within oxide-rich regions and blurring the distinction between planetary mantles and cores.

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