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Ag/Nb:SrTiO3(NSTO)/Ag and Au/NSTO/Ag structures were prepared and their current–voltage curves were studied in detail. The Ag/NSTO/Ag structure can demonstrate a pronounced resistive switching effect and the characteristics of its resistance change sequence as demonstrated in the I–V curves are significantly different from those of the Au/NSTO/Ag structure. Under a unipolar current, the Ag/NSTO/Ag structure translates first from a low-resistance state (LRS) to a high-resistance state (HRS) and then from the HRS to the LRS. However, the Au/NSTO/Ag structure only shows a transition from the HRS to the LRS. The phenomenon is analyzed taking into account the migration of oxygen ions and the electrochemical reaction of the Ag electrode, which lead to the formation of the Ag2O insulation layer as well as Ag conductive filaments in the Ag/NSTO/Ag structure and a change in the barrier height of the Au/NSTO interface. [ABSTRACT FROM AUTHOR]

Due to the great differences in electron pairing characteristics between the hole-type (p-type) high-temperature superconductor (HTS) and the electron-type (n-type) HTS, when the Cooper pairs enter from a p-type to an n-type HTS or an n-type to a p-type HTS, pairing adjustment or even the recombination of them will inevitably occur at the interface, and the superconducting current dominated by them will be bound to change. Therefore, it is possible to better understand the electron pairing mechanism of the HTS and develop new HTS junction devices by studying these changes. In this paper, p-/n-type YBa2Cu3O7−δ/Nd1.85Ce0.15CuO4 (YBCO/NCCO) heterostructures were prepared via pulsed laser deposition on (00l)-oriented single-crystal SrTiO3 substrates. X-ray diffraction measurements indicate that the NCCO films prepared on YBCO do not exhibit good c-axis epitaxial growth, while excellent c-axis epitaxial growth is obtained for YBCO/NCCO heterostructures with NCCO at the bottom. Due to the high-temperature oxygen atmosphere and the deoxygenation process, the superconducting electrical properties of the bilayer structure are seriously degraded, and it is not possible to obtain good superconducting electrical properties for both the upper and lower layers using the traditional preparation process based on an oxygen atmosphere. Subsequently, the effects of different growth atmospheres on the electrical properties of the YBCO superconductors were studied, and high-quality YBCO superconducting films could be grown in oxygen, nitrous oxide, and nitrogen atmospheres. However, the oxygen and nitrous oxide atmospheres degrade the superconducting electrical properties of the underlying NCCO layer, while the nitrogen atmosphere does not seem to affect it significantly. YBCO/NCCO superconducting bilayers with critical transition temperatures of 85 and 8 K for YBCO and NCCO, respectively, were finally prepared by growing NCCO in an oxygen atmosphere and YBCO in a nitrogen atmosphere using a low-temperature oxygenation process. The successful preparation of the p-/n-type HTS heterostructure will help further study on the HTS. [ABSTRACT FROM AUTHOR]

In this study, the epitaxial growth process of negative-type high-temperature superconducting thin film Nd1.85Ce0.15CuO4 (NCCO) by pulsed laser deposition is reported. First, the relationships between the heat treatment temperature of NCCO films, target-substrate distance, and oxygen pressure and the phase formation of a superconducting (00l)-T′ phase were investigated. It was found that a good superconducting (00l)-T′ phase could be epitaxially prepared from NCCO films only when the heat treatment temperature was higher than 650 °C. However, when the heat treatment temperature increased to 820 °C, NCCO films underwent thermal decomposition. The optimal oxygen pressure of phase formation for NCCO films, corresponding to the heat treatment temperature range of 650–800 °C, was given. Furthermore, the effect of deoxidization temperature on the superconductivity of NCCO films was also studied. The superconductivity of NCCO films was obtained only when the heat treatment temperature reaches 770 °C and the deoxidization temperature reaches 750 °C. The NCCO films obtained at 800 °C heat treatment temperature and 750 °C deoxidization temperature showed the best superconducting properties, and the initial superconducting transition temperature was as high as ∼30 K, with a transition width of only ∼0.15 K. [ABSTRACT FROM AUTHOR]