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

XPS measurements were carried out on Sr
2
Nb
2
O
7
and Sr
2
Ta
2
O
7
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 Sr
2
Nb
2
O
7
and Sr
2
Ta
2
O
7
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.