Constitutional and/or Thermal Vacancies in some Intermetallic Compounds

金属间化合物的非化学计量可能导致结构缺陷的存在，例如原子占据子晶格的原子位置而不是其自身的子晶格（反位原子）或缺陷原子种类的空位（结构空位）。金属间化合物中这种依赖于非化学计量比的结构缺陷及其性质已被正电子湮没方法研究，正电子湮没方法对空位和小空位团非常敏感，这是用其它方法很难研究的。本工作对某些金属间化合物的结构缺陷进行了正电子研究。对某些金属间化合物的热平衡缺陷和非平衡缺陷进行了原位测量和研究。正电子湮没寿命法已直接观察到一些重要金属间化合物中空位的形成和迁移特性，但常规的正电子湮没寿命测量难以在高温下进行。为了更方便地实现高温下特定材料的原位研究，<-gamma>作者所在的课题组研制了一台新的选能快正电子束β ^+符合寿命谱仪。新的正电子装置将成为研究高温下耐火材料晶格缺陷的一个非常有力的工具。

Nonstoichiometry of intermetallics may give rise to the existence of constitutional defects such as atoms occupying atomic sites of a sublattice other than its own sublattice (antisite atoms) or vacancies of deficient atomic species (constitutional vacancies). Such structural defects and their properties in intermetallics, which depend on nonstoichiometry, have been studied by positron annihilation methods.Positron annihilation methods are very sensitive to vacancies and small vacancy clusters which are quite difficult to be studied by other techniques. Positron studies of constitutional defects in some intermetallics have been carried out in this work. In-situ measurements of thermal equilibrium defects and studies of non-equilibrium defects on some intermetallics have been also done. The vacancy formation and migration properties in some important intermetallic componds have been directly observed by the positron-annihilation lifetime method.The conventional positron-lifetime measurement, however, is difficult to be carried out at high temperatures. In order to achieve in-situ studies of given materials at high temperatures more easily, a new beta^+_<-gamma> coincidence lifetime spectrometer using energy-selected fast-positron beam has been constructed by the author's group. The new positron apparatus will become a very powerful tool to study lattice defects at high temperatures in refractory materials.