The other set of doublets plus singlet appears at higher binding energies of _183.5, 185.9, and 193.1 eV, respectively,
which are due to ZrO2 and B2O3 [23,24].
One also observes that the ZrO2/ZrB2 and B2O3/ZrB2 peak intensity ratios are greater in the powder subjected to high-energy ball-milling in air.
Therefore, XPS has unambiguously detected the presence of ZrO2and B2O3in the as purchased and ball-milled ZrB2 powders,
and also shows them to be much more abundant in the ball-milled powder.
Also noted in the XPS spectra of the two powders are that the ZrO2 related peaks are more intense than the ZrB2 related peaks.
This observation, together with the oxygen contents that showed that the oxides are minor components and the fact that XPS is a surface technique,
indicate that ZrO2 and B2O3 cover the surface of the ZrB2 particles.
This hypothesis was further tested experimentally in the ball-milled powder by etching the surface with Ar+ ions to remove material followed by XPS data collection,
and also by TEM.