X-ray photoelectron spectra and the electronic band structure for non-centrosymmetric Bi2ZnB2O7 nonlinear single crystal

We have synthesized and characterized the bismuth borate Bi2ZnB2O7 single crystals. The results of the experimental measurements of the X-ray diffraction (XRD) and X-ray photoelectron spectrum (XPS) along with an ab initio theoretical study of the electronic band structure, and density of states, are reported. The theoretical calculations are based on crystal structure built from our experimentally determined atomic parameters. The theoretical calculations have been done by using the full potential linearized augmented plane wave (FP-LAPW) method. We applied the Perdew–Burke–Ernzerhof generalized gradient approximation (GGA) and the Engel–Vosko GGA formalism. The observed XPS pattern is in good agreement with the theoretical one, confirming the pure phase of Bi2ZnB2O7. The purity and composition of the as-prepared sample are studied by XPS analysis. XPS measurements show that the bismuth possesses +3 valence state, and Zn and B species exist only in the traditional valence states of Zn2+ and B3+. The O 1s spectra are broad and asymmetric and can be deconvoluted into two peaks. The lower and higher binding energy peaks (around 530.1 and 531.5 eV) are assigned to originate from O 1s(1) and O 1s(2) terms, respectively, which are attributed to non-bridging oxygen (B–O− bonds) and bridging oxygen (B–O–B bonds), respectively. Our calculations show that Bi2ZnB2O7 has an indirect energy gap and that Bi–O bonds are of strong covalent character.