Preparation Of YBa₂Cu₃O_7-x Superconductors By Sol-Gel Method

Currently, Magnetron Sputtering, Pulsed Laser Deposition (PLD), Metalorganic Chemical Vapor Deposition(MOCVD), as main methods for fabrication of YBa2Cu3O7-x (YBCO or Y123) films, involves expensive vacuum equipments. Due to the low cost and the capability of large-scale fabrication, the sol-gel method, however, attracted great interests. The aim of this paper is to explore a suitable sol-gel method to prepare the YBCO superconducting films for the application on metallic and silicon substrates. Different kinds of fluorine-contained and fluorine-free sols were prepared, and with the LaAlO3 singe crystal as substrate, the so-called "YBCO" films were respectively fabricated. In addition, using the fluorine-free sol, superfine YBCO powders were fabricated, and the YSZ films as the buffer layer for YBCO on the silicon were also analyzed. The compositions and structures of YBCO films, powders, are respectively analyzed using XPS, SEM, TEM, XRD and so on. The results are as follows:(1) With acetates as starting material, methoxyethanol or proponic acid as solution, stable fluorine-free YBa2Cu3O7-x sols can be prepared by using suitable complexing agents. After modifying the All-TFA solution reported by many papers, with partial trifluoroacetates as precursors, two kinds of stable fluorine-contained YBCO sols were also fabricated.(2) Through the fluorine-free sol-gel method, superfine YBCO powders with highreactivity were fabricated. XRD and TEM indicated that the powders werebelonging to orthorhombic perovskite structure, and the diameters of the powders ranged from tens to hundreds of nanometers. The oxygen amount in the YBCO unit cell is about 6.64, and therefore, the powders can be regarded as YBa2Cu3O6.64. Using these powders YBCO bulks with high critical temperature(92.5K) were obtained.(3) A new fluorine-contained sol-gel method, namely, (Y,Ba)-TFA method, was put forward by reducing the amount of trifluoroacetates in the sol. Compared to the All-TFA method, the YBCO films prepared by this method have high surface quality and large density, and the duration of the heat treatment was greatly shortened.