Research Of YBa₂Cu₃O_7-δ Powders And Sintered Bulks

YBa₂Cu₃O_7-8 series is one of the most useful high temperature superconductors for various applications. The sintering process is the traditional preparation method of YBa₂Cu₃O_7-8 superconductor. It is easy to prepare and time-saving. It is also very important for the foundamental research and provides some basic information for other technics.The solid state reaction method (sintering process) was used for the synthesis of YBa₂Cu₃O_7-8 powders and bulk superconductors. The microstructure, superconducting properties and trapped magnetic field was also investigated.The YBa₂Cu₃O_7-8 powder was synthesized by solid state reaction method with two times milling and sintering process. The DTA-TG result showed that the solid state reaction temperature of Y123 phase is in the range of 850°C 950°C. It is found that single phase Y123 powder can be fabricated between 880 °C and 920°C, and with sintering time longer than 12h.YBa₂Cu₃O_7-8 bulk superconductors have been prepared with different grain size of precursor Y123 powder and with different temperature between sintering temperature and peritectic temperature. The density of the samples before and after sintering is different when using initial powders of different grain size and different moulding pressure. The higher the sintering temperature, the bigger the sintered density of the samples, and the more shrinkage of the sample in the radial direction.Ca doping may effectively enhance the solid reaction rate of Y_1-xCa_xBa₂Cu₃O_7-5 superconductor, and improve the escaping rate of the gas during the sintering process. The bigger the Ca doping content X, the higher the density p of the sample after sintering.The effects of sintering temperature, time, the heating and cooling temperature rate and etc on the microstructure and physical properties of YBa₂Cu₃O_7-8 superconductor have been investigated. Nearly single phase Y123 pellets were fabricated with the sintering temperatures of 910°C and 920°C. The YBCO bulks sintered in the range of 910 °C 930 °C showed superconducting properties, but there was no obvious superconducting properties when the sample sintered at 950°C. It is found that high quality Y123 pellets can be obtained with sintering temperature of 920°C and dwelling time of 24h and the heating and cooling temperature rate of 120°C/h.