Equiatomic CoCrFeNi Thin Films on C‐Sapphire: The Role of Twins and Orientation Relationships

Face‐centered cubic (fcc) metals deposited onto crystalline substrates grow heteroepitaxially with specific orientation relationships (ORs). The ORs depend on a number of factors including lattice mismatch, bonding and the relative symmetry between the surface and the film. Less explored factors include defects like growth and annealing twins. In this study, a high density of nanotwins in as‐deposited films delay grain growth of OR1 (, ) grains up to 0.56 T_m. A new OR with respect to the c‐sapphire substrate is found, compared to the well‐known OR1 and OR2 which grow with the . This is named OR3, grows above 0.56 T_m with . The OR3 growth is related to strain and defect energy advantage. An unusual OR accompanies OR3 in most films, occupying an area fraction of >0.3. A minute (<0.05) but consistent fractions of , , , and all parallel to and related to annealing twins in exact and near and grains are observed. The study opens new directions in the crystallography of ORs, considering the role of twins in addition to the surface and strain energies.