A method for forming a coated substrate is disclosed. The method comprises depositing an undercoating layer and depositing a functional coating comprising a material which can be present in more than one crystal structure over the undercoating layer, wherein there is a critical deposition thickness at which the functional coating transforms from a first polycrystalline film made up predominantly of the material having a first crystal structure to a second polycrystalline film made up predominantly of the same material having a second crystal structure.