YBCO熔融织构准单晶中的进氧和脱氧扩散研究

采用热重法研究了YBCO熔融织构准单晶中氧的化学扩散过程. 与以往的实验不同，采用固定 氧偏压变化温度的方法获得氧浓度梯度. 拟合实验所得重量等温弛豫曲线可知，在375—600 ℃温区内，熔融织构准单晶的氧化学扩散系数比单晶体高出约50％，但都约为10^{-10c m2s-1，激活能为～1eV. 对YBCO熔融织构准单晶中的进氧和脱氧研 究表 明两者具有相同的速率，证实实验过程中环境氧分压的改变会导致进氧和脱氧过程不一致. 关键词： 高温超导 氧扩散 熔融织构 热重法}

The oxygen in- and out-diffusion behavior in melt-textured YBCO measured by thermogravimetry

The chemical oxygen in- and out-diffusion in melt-textured YBa₂Cu ₃O_7-δ（YBCO）is investigated by thermogravimetry. The weight relaxations resulting from the sudden change of temperature at a fixed oxygen partial pressure of 033×１０⁵Pa are recorded. By fitting the isothermal curves, the chemical diffusion coefficients at 375—600℃ are determined. It is found that the resultant numerical values for melt-textured YBCO are larger than that of crushed single crystal YBCO obtained in our previous study by about 50%, whereas all of them are of the order of 10^-10cm²s^-1 . The activation energies for both samples are estimated as ～1eV. It is believed that those values represent the nature of the lattice diffusion. The oxygen diffusion in me lt-textured-grown-YBCO is attributed to the YBCO matrix and the micro-cracks are responsible for the huge diffusion coefficients. Moreover, the same kinetics o f in- and out-diffusion is confirmed to be intrinsic, and it suggests that the d ifferent in- and out-diffusion coefficients measured in other works are controll ed by the large concentration gradient and the shell effect.