$\mathrm{HfZr}{\mathrm{O}}_2$(HZO) is a promising ferroelectric material compatible with CMOS technology, retaining functionality at nanometer-scale thicknesses. Its ferroelectricity arises from metastable polar phases—orthorhombic ($Pca{2}_1$) and rhombohedral (R3m)–coexisting with the thermodynamically stable, non-polar monoclinic phase ($P{2}_1/c$). Accurate quantification of these coexisting phases is essential for optimizing device performance. Here, we use first-principles calculations to estimate core-level shifts in the O 1s X-ray photoelectron spectroscopy (XPS) peak, revealing a distinct, up to 0.84 eV higher binding energy component for oxygen atoms in the polar sublattice compared to those in non-polar environments. These shifts incorporate both initial and final state effects in photoemission. Experimental validation through X-ray diffraction (XRD) and XPS on HZO films with varying phase composition confirms our predictions. Our findings provide a clear, spectroscopically accessible fingerprint to distinguish polar and non-polar phases in HZO via O 1s XPS analysis, offering a practical tool for phase quantification and enabling targeted integration of ferroelectricity in advanced nanoelectronic devices.

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• Ferroelectrics
• Density functional theory
• X-ray diffraction
• X-ray photoelectron spectroscopy