Electronic parameters of Sr2M2O7 (M = V, Nb, Ta) and Sr-O chemical bonding

XPS measurements were carried out on Sr₂Nb₂O₇ and Sr₂Ta₂O₇ powder samples, which were synthesized using standard solid state method. The binding energy differences between the O 1s and cation core level, Δ(O-Sr) = BE(O 1s) - BE(Sr 3d_5/2), was used to characterize the valence electron transfer on the formation of the Sr-O bonds. The chemical bonding effects were considered on the basis of our XPS results for Sr₂Nb₂O₇ and Sr₂Ta₂O₇ and the previously published structural and XPS data for other Sr-oxide compounds. A new empirical relationship between Δ(O-Sr) and L(Sr-O) was obtained. Possible applications of the relationship are discussed.