B/MgB_2异质结热稳定性的研究

Thermal Stability of B/MgB_2 Heterojunction

通过热力学计算B-Mg B2体系中可能发生化学反应的标准吉布斯自由能变化值（ΔrGθT）随温度变化的关系,对其体系的热稳定性进行了探讨。综合应用X射线衍射、标准四线法和扫描电子显微镜对在氩气气压为103Pa条件下993 K退火10~30 min的B/Mg B2异质结试样的晶体结构、超导电学特性及断面结构进行了测量研究。实验结果表明,B-Mg B2体系在973 K以下温度范围内能保持良好的热稳定性,但随着背景气压降低,Mg B2会发生缓慢分解,使得异质结微观结构和超导特性受到影响。

The B-Mg B_2 heterojunction was fabricated by hybrid physical chemical vapor deposition and chemical vapor deposition on Al_2O_3（ 0001） substrate. The thermodynamic characteristics of the B-Mg B_2 heterojunction were theoretically analyzed by calculating the temperature dependent Gibbs free energy and experimentally measured. The influence of the annealing temperature,annealing time and argon pressure on the microstructures,superconducting behavior and interface structures was investigated with X-ray diffraction,scanning electron microscopy and four-point probe. The results show that the Ar-pressure significantly affects the thermal stability of the B-Mg B_2 heterojunction. To be specific,annealed at 993 K for 10 ~ 30 min,and at 103 Pa of argon,the B-Mg B_2 heterojunction was highly stable in temperature range below 973 K. As the Ar-pressure decreased,the Mg B_2 slowly decomposed,accompanied by deteriorations of both the crystallinity and superconducting properties of the B-Mg B_2 heterojunction.