Comparative study of the core level photoemission of the ZrB2 and ZrB12

X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) were used to investigate the binding energies and valence band for ZrB₂ and ZrB₁₂. The Zr 3d and B 1s core levels were identified. The Zr 3d core level shows a spin–orbit split 3d_5/2 and 3d_3/2 while that for B 1s core level exhibited a single symmetric peak, these being typical of zirconium and boride signals. Comparing the Zr 3d and B 1s core levels with metallic Zr, B₂O₃ and ZrO₂ reference materials only a negative chemical shift for Zr 3d associated to ZrB₂ was observed, which suggests that the charge transfer model based on the concept of electronegativity was not applicable to explain the superconductivity in the ZrB₁₂ sample. The measured valence band using UPS is consistent with the band-structure calculations indicating a higher density of states (DOS) at E_F for ZrB₁₂ respect to ZrB₂. Finally, we found that the weak mixed B-p and Zr-d states for ZrB₁₂ is crucial for the superconductivity due to the state population increased the DOS at the E_F.