Resistance switching (RS) characteristics of Al/ZnO:Li/LaB 6 and Al/ZnO:Li/La 2 O 3 /LaB 6 devices in which LaB 6 and lithium-doped ZnO (ZnO:Li) films are regarded as shallow work function metal and p-type semiconductor, respectively, are studied. The alternation from bistable unipolar memory switching (URS) to monostable threshold switching (MTS) in the Al/ZnO:Li/LaB 6 device is observed. These two switching behaviors can be activated separately depending on the polarity of applied dc voltage: with a positive polarity the URS behavior is measured, while the MTS behavior is observed with a negative polarity. With increase in the number of switching cycles, the MTS and URS behaviors irreversibly transform to bipolar resistance switching (BRS) behavior. The Al/ZnO:Li/La 2 O 3 /LaB 6 device shows only the BRS behavior, but after certain number of cycles device serves as a rectifying diode. On the basis of the I-V and C-V characteristics, it is concluded that RS properties depend on the barrier height and reactivity between LaB 6 metal and ZnO:Li oxide.
A new way of preparing Y–Ba–Cu–O (YBCO) high-temperature superconducting (HTSC) materials has been developed using the sol–gel processing technique based on new and convenient precursors that are stable in air and have high compatibility with each other. For the preparation of HTSC materials, instead of unstable copper alkoxides, the use of chelate type copper compounds as highly effective and stable precursors has been suggested. These have been prepared by the reaction of copper hydroxide with the corresponding (mono, di, tri)ethanolamines. A new method of preparing yttrium precursors on the basis of coordination acetylacetonate type polymer has been suggested. A reaction with bidentate type complex forming solvents such as 2-alkoxyethanols results in the formation of the complex type yttrium alkoxides. Superconducting YBCO ceramic materials have been developed, both films (applied on yttrium stabilized zirconia) and powders, using the sol–gel method based on the new yttrium and copper precursors. X-ray and thermal analyses of the synthesized materials have been carried out. The transition temperature into the superconducting state, T(0)c, and the temperature interval of this transition, ΔT, have been found to be T(0)c = 84 and 88 K and ΔT = 4 and 3 K for YBa2Cu3O7−x bulk ceramics and thin films, respectively.
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