X-ray diffraction and extended X-ray absorption fine structure study of epitaxial mixed ternary bixbyite Pr_xY_2-xO₃ (x = 0-2) films on Si (111)

Ternary single crystalline bixbyite Pr_xY_2-xO ₃ films over the full stoichiometry range (x = 0-2) 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 L_III 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 Pr_xY_2-xO₃ 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.