The interface and layer structure of praseodymium (Pr) oxide layers grown on Si(0 0 1) from a high-temperature effusion cell are studied using grazing incidence X-ray diffraction. Due to the interdiffusion of praseodymium and silicon atoms, Pr silicide forms in the layers. We find that Pr silicide is the favorable structure under oxygen deficient growth conditions in the Pr oxide layer. To avoid the silicidation, additional oxygen must be supplied. The formation of Pr silicide is suppressed for layers grown with an oxygen partial pressure of 10 (7) mbar at a substrate temperature of 700 degrees C. (c) 2008 Elsevier B. V. All rights reserved.