Yttrium-induced structural changes in sputtered Ti1−xAlxN thin films

Metastable Ti1−xAlxN thin films synthesized by plasma-assisted vapour deposition crystallize in the industrially preferred cubic NaCl (c) structure with AlN mole fractions (x) ⩽ 0.7. We reveal, via X-ray diffraction and transmission electron microscopy, that the addition of yttrium to c-Ti1−xAlxN shifts the solubility limit to lower AlN contents, resulting in mixed c- and hexagonal ZnS–wurtzite (w) phase (Ti1−xAlx)1−yYyN coatings. Ab initio calculations yield a ∼23% decrease in the solubility limit in c-Ti1−xAlxN, from x ∼ 0.69 to 0.56 with the addition of y = 12.5 at.% Y.