XANES and RBS were used to explore the structural phase and composition transitions of ultrathin films with Ti_(1−x)Zn_2xO₂ stoichiometries, from very low (∼0.5 at.%) to high (∼25 at.%) titanium content. In this way, the coordination chemistry of Ti⁴⁺ and Zn²⁺ cations was examined for a wide range of oxide compositions.