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X-ray study of the atomic charge densities in MgO, CaO, SrO and BaO
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1978
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X-ray CrystallographyX-ray SpectroscopyEngineeringOxygen IonAtomic Charge DensitiesX-ray StudyInorganic MaterialOxygen PositionCalcium AluminateIonic CharacterMaterials SciencePhysicsAtomic PhysicsCrystallographyNatural SciencesX-ray DiffractionApplied PhysicsCondensed Matter PhysicsIon Structure
Accurate X-ray structure factors of CaO, SrO and BaO were measured at 293 K from single crystals and analysed together with the data of Sanger [Acta Cryst. (1969), A25, 694-702] on MgO. The oxygen ion is seen to suffer an average compression and a fourth-order cubic harmonic type deformation, as compared to the atomic superposition model, yielding a lower average charge density in the surrounding region and a charge transfer from [111] to the [100] direction. These features strengthen with increasing atomic number of the cation. Mg and Ca show a weak broadening. About nine electrons are localized around the oxygen position. The tenth electron of O2- is more widely distributed. The electron counts of the cation correspond most closely to Mg+, Ca2+, Sr2+ and Ba2+. The results confirm the dominance of ionic character and increase of ionicity with increasing atomic number of the cation.