从高温超导体比热的测量探讨提高J_c的途径

SPECIFIC HEAT STUDY OF HIGH Tc SUPERCONDUCTOR TO INCREASE ITS J_c

采用连续绝热法测量YBa_2M_XCu_(3-x)O_(7-δ)高温氧化物超导体(M=Ag,Pb)的临界温度T_C及80～110K温区的比热C_p。结合该样品临界电流密度J_e的测量结果,该文提出,对于此类粉末固相反应制备的烧结氧化物高温超导体YBa_2M_xCu_(3-x)O_(7-δ),M可能并未取代Cu进入晶格,而是使晶格趋于金属化,晶界层性质对J_e的影响,比超导含量对J_e影响大得多。该文并尝试对超导含量及晶界作了某些定量计算。

The specific heat of ceramic high. Tc superconductor VBa2M2Cu3-xO7-y(M = Pb,Ag) L measured in the temperature range from. 80-110K usingadiabatic continuous heating method. The results show that doping have no obvious influence on Tc of above samples.However the jumps of specific heat at Tc decrease greatly due to doping, while the results presented by Ma's group make evidence that Jc in doping samples increase remarkably using the. same samples.According to experimental results we can obtain the cntropic changes near Tc by integrating δCp/T and then do the quantitative analysis about contents of superconductor in YBa2MxCu3-xO7-x We find that the contents of superconductor in doping samples have decreased to 40% and 45% of non -doping one for Ag and Pb respectively.It confirms that Jc has no obvious relation to the content of superconductor in sample, but Jc is greatly affected by impurity phase.Since the doping elements couldn't subs-titude Cu in 123 phase, but form some kind of metal oxide along the gr ain boundaries, which improves conductivity of grain boundaries.It has been roughly estimated that grain boundaries of doping Ag and Pb samples are 36% and 30% more than that of non-doping one. It shows that doping can not only improve the properties of grain boudaries, but also enlarge grain boundaries.Jc will decrease if the increased width is beyond a specific limit in short coherence length high Tc ceramic super condutor. In conclusion, it is very imporment to investigate various doping samples and calculate the entropic changes by integrating δC/T then find an appropriate doping proportion.