title: Phase transformations and metallization of magnesium oxide at high pressure and temperature.
abstract: 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 terapascals (TPa) reveal a sequence of two phase transformations: from B1 (sodium chloride) to B2 (cesium chloride) crystal structures above 0.36 TPa, and 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.
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, NW, Washington, DC 20015, USA. stewartmcwilliams@gmail.com
authors.forename: R Stewart
authors.initials: RS
authors.lastname: McWilliams
authors.forename: Dylan K
authors.initials: DK
authors.lastname: Spaulding
authors.forename: Jon H
authors.initials: JH
authors.lastname: Eggert
authors.forename: Peter M
authors.initials: PM
authors.lastname: Celliers
authors.forename: Damien G
authors.initials: DG
authors.lastname: Hicks
authors.forename: Raymond F
authors.initials: RF
authors.lastname: Smith
authors.forename: Gilbert W
authors.initials: GW
authors.lastname: Collins
authors.forename: Raymond
authors.initials: R
authors.lastname: Jeanloz