Oxygen Vacancy Effect In SrCoO_x Thin Films

Oxygen vacancy defect is an important factor for the rich functionality of the oxide.Oxygen vacancies can be used to control the electrical,magnetic,superconducting and optical properties.According to the survey,SrCoO_x?x=2.5³?as a kind of ideal variable valence transition metal oxides have attracted many scientists to explore.In this paper,we investigate the effect of oxygen vacancy on SrCoO_x single phase thin films and SrCoO_x-CeO₂ composite films.1.We used the pulsed laser deposition?PLD?to parpare brownmillerite type SrCoO_x?BM-SCO?films.The structure and properties of BM-SCO were characterized by XRD,AFM,XPS,PPMS and so on.After that,the oxygen vacancies in SrCoO_x films were controlled by chemical oxidation,electrochemical oxygenation and post annealing.A mixed-phase of BM-SCO and P-SCO?Mix-SCO?was observed,and oxygen intercalation drive the antiferromagnetic phase to ferromagnetic phase?T_c¹80K?,as annealed in lower temperature?250?<T<600??.We also found that in post-annealing under 600?exhibited a complete phase transition from the BM-SCO to the P-SCO??⁰.25?.The BM-SCO can be completely converted to SrCoO₃ without oxygen vacancies by chemical oxidation.However,in the vacuum atmosphere the sample after chemical oxidation is not stable,and it's easy to lose the oxygen in lattice.2.The SrCoO_x-CeO₂ nanocomposite films with ordered structure were prepared by pulsed laser deposition?PLD?.We found that the oxygen content of SrCoO_x phase in the composite film was increased,and convert to P-SCO due to the oxidation of CeO₂ phase.It has been found that SrCoO_x and CeO₂ phase grow alternatively and form a vertically aligned columnar structure in the nanocomposite films.And the CeO₂ nanopillars with a diameter of⁵ nm,the SrCoO_x nanopillars with a diameter of¹0 nm.Besides,the structure of SrCoO_x in SrCoO_x-CeO₂ composite thin films can be controlled by changing the laser energy density?E_j?.When the E_j is high,the P-SCO is favorable.When the E_j is low,the BM-SCO is prepared.The SrCoO_x-CeO₂ composite films with the molar ratio of 25:75,50:50 and 0:100 were prepared.It was found that the higher proportion of CeO₂ in the composite films was favorable for the preparation of P-SCO.We also found that the SrCoO_x-CeO₂ composite films show antiferromagnetic,consistent with BM-SCO thin film,SrCoO_x-CeO₂ composite films and BM-SCO films were semiconductor,but the resistivity of the composite films is two orders of magnitude lower than in situ BM-SCO film.There may be two reasons:?a?the oxygen content of SrCoO_x increases,and the conductivity increases;?b?the interface increases more oxygen vacancies,which leads to the increase of conductivity.