The Study on the Effect of Nonstoichiometry on Thermal Equilibrium Defects in Intermetallic Compounds by Positron Annihilation

用正电子湮没法研究了非化学计量对金属间化合物热平衡缺陷的影响。利用正电子寿命谱、多普勒展宽谱、湮灭辐射的二维角相关和慢正电子分析对正电子湮灭进行了测量。得到了以下结果：(1)TiAl和TiAl_3中非化学计量引入的缺陷：测量了正电子湮灭特性作为上述合金在其一相区合金成分的函数。结果发现，由非化学计量成分引入的空位型缺陷的浓度远远低于正电子湮没技术的检测限。这一结果清楚地表明，多余的合金元素形成了相反的缺陷。利用本项目首次开发的^<48>V位源进行的热平衡实验表明，与纯金属相比，这些金属间化合物中引入了更多的空位。(2)测定β′-AgZn中电子的三维动量空间密度：采用图像重建技术对不同晶体取向的二维acar光谱进行测量，测定β′-AgZn中电子的三维动量空间密度。实验测定的密度与理论预期的密度吻合得很好。在这种情况下，多余的合金元素也占据了相反的晶格点。此外，还成功地测定了NiAl、Ni_3Al和NbSe_2中的第三密度。

The effect of nonstoichiometry on thermal equilibrium defects in intermetallic compounds was studied by positron annihilation. The measurements of positron annihilation were carried out by means of the positrdn lifetime spectroscopy, the Doppler broadening spectroscopy, the two dimensional angular correlation of annihilation radiations and the slow positron analysis. The following results were obtained :(1) Defects introduced by nonstoichiometry in TiAl and TiAl_3 :The positron annihilation characteristics were measured as a function of the alloy compositions of the above alloys in their one phase region. As a result, it was found that the concentration of vacancy-type defects introduced by the nonstoichiometric composition is quite lower than the detection limit of the positron annihilation technique. This result clearly shows that the extra alloy elements form the antisite defects. From the thermal equilibrium experiment performed by the use of ^<48>V positon source, which was for the first time developed in the present research program, a greater num ber of divacancies were introduced in these intermetallic compounds as compared with In pure metals.(2) Determination of three dimensional momentum space density of electrons in beta'-AgZn :By the measurements of 2D-ACAR spectra with different crystal orientations followed the image reconstruction technique, the three dimensional momentum space density of electrons in beta'-AgZn was determined. The experimentally determined density coincides well with the theoretically expected one. In this case, the extra alloy elements also occupy the antisite lalttice points.In addition, the determination of thd densities in NiAl, Ni_3Al and NbSe_2 was carried out successfully.