Thin films of oxygen-deficient perovskite phases by pulsed-laser ablation of strontium titanate

An oxygen-deficient phase has been formed by pulsed-laser ablation of strontium titanate under vacuum conditions (10(-7) mbar). By the complementary use of Rutherford backscattering spectrometry and x-ray diffraction, the composition and structure of films were determined. A large oxygen deficiency is revealed in the films as the corresponding formula is SrTiO2.5. This understoichiometry means that Ti3+ are present in such films, while only Ti4+ is observed in stoichiometric compound (SrTiO3). The presence of Ti3+ species in the SrTiO2.5 films was checked by x-ray absorption spectroscopy. The SrTiO2.5 films were found to crystallize in the cubic perovskite structure with a lattice parameter of 0.40 nm, considerably higher than that of the stoichiometric compound (0.39 nm). The SrTiO2.5 films were epitaxially grown on MgO single-crystal substrates, with a "cube-on-cube" in-plane orientation with the substrate. In contrary to stoichiometric SrTiO3 films which are perfectly insulating, the SrTiO2.5 films were found to be conductor or semiconductor at room temperature, depending on the growth temperature. Resistivities at room temperature in the 10(-3)-10(-2) Omega cm range are thus obtained.