氟化铅晶体中针状缺陷的成因研究

STUDY ON THE ORIGIN OF NEEDLE_LIKE DEFECTS IN LEAD FLUORIDE CRYSTAL

利用光学显微镜观察了存在于立方氟化铅晶体中的针状结构缺陷．根据ＸＲＤ，ＥＭＰＡ和透射光谱测试以及原料的ＸＲＤ和ＤＴＡ特征，认为这种针状结构缺陷属于斜方氟化铅．对试样的退火实验证实，在高于氟化铅相变温度的条件下退火若干小时可以有效地消除这种缺陷．在上述基础上提出针状缺陷的形成与热应力作用下部分β－ＰｂＦ２向α－ＰｂＦ２的相转变有关，而针状缺陷的消除则被归因于退火后热应力的释放和在高于３６５℃温度下α－ＰｂＦ２向β－ＰｂＦ２的相转变．

Needle_like structural defects existing in cubic PbF2 crystal were observed with optical microscope. They distribute along and direction of -PbF2 matrix. By means of XRD, EMPA, transmission spectra as well as XRD and DTA characteristics of the raw materials, these defects are proposed to be orthorhombic PbF2. Annealing experiments on the sample confirm that these defects can be eliminated effectively when the temperature is over the phase transition temperature. So the mechanism on the forming of these defects can be explained to be -PbF2 changes from cubic to orthorhombic phase at thermal strains. And the disappearing of needle_like defects after annealing is ascribed to the release of thermal strain and phase transition from -PbF2 to -PbF2 when the temperature is over 365 .