X-ray diffraction and extended X-ray absorption fine structure study of epitaxial mixed ternary bixbyite PrxY2−xO3 (x = 0–2) films on Si (111)

Ternary single crystalline bixbyite PrxY2xO3 films over the full stoichiometry range (x¼0–2) have been epitaxially grown on Si (111) with tailored electronic and crystallographic structure. In this work, we present a detailed study of their local atomic environment by extended X-ray absorption fine structure at both Y K and Pr LIII edges, in combination with complementary high resolution x-ray diffraction measurements. The local structure exhibits systematic variations as a function of the film composition. The cation coordination in the second and third coordination shells changes with composition and is equal to the average concentration, implying that the PrxY2xO3 films are indeed fully mixed and have a local bixbyite structure with random atomic-scale ordering. A clear deviation from the virtual crystal approximation for the cation-oxygen bond lengths is detected. This demonstrates that the observed Vegard’s law for the lattice variation as a function of composition is based microscopically on a more complex scheme related to local structural distortions which accommodate the different cation–oxygen bond lengths.