Synthesis and Characterization of Refractory Oxides Doped with Transition Metal Ions

In this study, the oxygen-deficient TiO 2 , SrTiO 3 systems and transition metal ion (Cr or V) doped TiO 2 , SrTiO 3 and SrZrO 3 systems have been investigated. We prepare samples as polycrystals, single crystals and thin films for various desires. Their structural, physical and electronic properties are measured by bulk-sensitive techniques (X-Ray Diffraction, SQUID and Electro Paramagnetic Resonance) or surface-sensitive techniques (Photoemission spectroscopy and X-ray absorption spectroscopy). The measurement of SQUID and EPR shows not only their magnetic properties but also the valence state of Cr dopant. We verify the valence state of Cr ions in Cr:TiO 2 , Cr:SrTiO 3 and Cr:SrZrO 3 with three forms of samples, polycrystals, single crystals or films. We try to find the key parameters of sample synthesis which control the valence state of Cr ions. The cluster containg various valence state of Cr or the segregated phases such as CrO 3 or SrCrO 4 can be formed when the sample was synthesized under O 2 rich environment. Cr ions in those systems tend to be oxidized easily under O 2 rich environment. The surface properties of Cr doped SrZrO 3 films are also discussed. We find the synthesis conditions which influence on not only the behavior of Cr ions but also the resistive-switching behaviors. Various resistive-switching behaviors seem to depend on the surface chemistry of films. We found that the accumulation of Cr 3+ on film surface provides a clean interface without any non-stoichiometric oxides and this sharp interface termination resulted in a good performance of resistive-switching. magnetic semiconductor, resistive-switching random access memory