title: B1-b2 transition in calcium oxide from shock-wave and diamond-cell experiments.
abstract: Volume and structural data obtained by shock-wave and diamond-cell techniques demonstrate that calcium oxide transforms from the B1 (sodium chloride type) to the B2 (cesium chloride type) structure at 60 to 70 gigapascals (0.6 to 0.7 megabar) with a volume decrease of 11 percent. The agreement between the shockwave and diamond-cell results independently confirms the ruby-fluorescence pressure scale to about 65 gigapascals. The shock-wave data agree closely with ultrasonic measurements on the B1 phase and also agree satisfactorily with equations of state derived from ab initio calculations. The discovery of this B1-B2 transition is significant in that it allows considerable enrichment of calcium components in the earth's lower mantle, which is consistent with inhomogeneous accretion theories.
authors.forename: R
authors.initials: R
authors.lastname: Jeanloz
authors.forename: T J
authors.initials: TJ
authors.lastname: Ahrens
authors.forename: H K
authors.initials: HK
authors.lastname: Mao
authors.forename: P M
authors.initials: PM
authors.lastname: Bell