Besides its many applications in electronics, photonics, and catalysis, ZnO has also been extensively used as the pigment zinc white ever since its introduction in the first half of the 19th century. It is shown here that zinc whites (ZnO formed through zinc vapor oxidation) form a chemically binary system, with each of the sub-micrometric crystallites belonging to either of two distinct classes. The observation of the two classes is done based on X-ray absorption nanospectroscopy and was determined to be caused by differences in the populations of anisotropic crystal defects. A theoretical assessment of the vapor oxidation synthesis method is formulated that predicts that the binary distinction in crystal defect populations is caused by local variations in synthesis parameters. As the crystal defect population in ZnO has been shown to be related to its catalytic properties, these results provide fundamental insights on the link between the intrinsic properties of zinc white and its degradation issues in oil paint.
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