Mechanical and tribological properties of CdO + SnO₂ thin films prepared by sol–gel

We report the mechanical and tribological properties of transparent conductive oxide CdO + SnO₂ coatings. The films were deposited on glass substrates by the sol–gel technique using, as precursor solution, a mixture of CdO and SnO₂ solutions obtained at room temperature. Depending on the Sn atomic concentration percentage values the X-ray diffraction patterns show three types of films constituted of (1) CdO + Cd₂SnO₄, (2) Cd₂SnO₄ and (3) Cd₂SnO₄ + CdSnO₃ crystals. Reciprocal microfriction tests revealed that films with Cd₂SnO₄ phase have friction values in the range 0.48–0.51 and a low wear rate of ~5 × 10⁻⁵ mm³ N⁻¹ m⁻¹. Nanoindentation tests have shown an increment of the elastic modulus from 50 GPa for CdO + Cd₂SnO₄ films to 90 GPa for Cd₂SnO₄ films, while the hardest coating was the one constituted by Cd₂SnO₄ crystals with H = 5.7 GPa, comparable to the hardness and elastic modulus reported for ITO films.