Core level photoemission spectroscopy and chemical bonding in Sr2Ta2O7

Electronic parameters of constituent element core levels of strontium pyrotantalate (Sr2Ta2O7) were measured with X-ray photoelectron spectroscopy (XPS). The Sr2Ta2O7 powder sample was synthesized using standard solid state method. The valence electron transfer on the formation of the Sr-O and Ta-O bonds was characterized by the binding energy differences between the O 1s and cation core levels, Δ(O-Sr) = BE(O 1s) − BE(Sr 3d5/2) and Δ(O-Ta) = BE(O 1s) − BE(Ta 4f7/2). The chemical bonding effects were considered on the basis of our XPS results for Sr2Ta2O7 and earlier published structural and XPS data for other Sr- and Ta-containing oxide compounds. The new data point for Sr2Ta2O7 is consistent with the previously derived relationship for a set of Sr-bearing oxides. The binding energy difference Δ(O-Sr) was found to decrease with increasing bond distance L(Sr-O).