What is it about?
An anomaly of the temperature dependence of the unit cell parameter has been observed for b-PbF2 single crystals at 200 K that is interpreted as a phase transition to a pseudocubic lattice. Such a pseudocubic phase is observable at room temperature after uniaxial plastic deformation of the bulk single crystals. The structural aspects of the P-3ma transition have been established. The as-grown crystals of ct-PbF2 phase are shown to undergo a phase transition at 100 K.
Featured Image
Why is it important?
The importance of the [111] plane in the P-3mo transition was complemented by the orienta- tion characteristics of the samples in the two-phase state obtained by uniaxial deformation. It was established that, after elastic deformation of the f3-PbF 2 crystals along the [111] direction on the stressed [111] face of the sample, a thin layer of the orthorhombic phase emerges. For other directions it is absent. The layer has a single crystal quality with the normal along the [010]ortho. The same occurs in plate-like samples after a low level plastic deformation (see Figure 1). The layer thickness in this case is larger for greater deformation. If the deformation exceeds a few percent, additional reflections emerge on the diffractograms.
Perspectives
The unstressed crystals of pure a and 13phases give a small light output after y- and X-ray excitation. As constructed from pure samples, the light output from the two-phase samples ob- tained after plastic deformation and pure orthorhombic phase obtained after hydrostatic pressure treatment increases by one or sometimes by two orders of magnitude. What is the nature of such an increase? As the chemical composition of all types of the samples is the same, only real structure differences can be responsible for the mechanism of light output increase. These results suggest the conclusion that the lattice distortions and stressed interphase regions can be respon- sible for the increase. It means that the use of the PbF 2 crystals as high output scintillators can be achieved if special techniques of crystal treatment can be designed that produce crystals in which the proportion of distorted regions is comparable with the whole volume of the scintillator.
Dr Bagautdin Bagautdinov
Read the Original
This page is a summary of: Structure Characteristics of Cubic and Orthorhombic Phases of High Density Scintillator Pbf2 from 4.2–300 K, MRS Proceedings, January 1994, Springer Science + Business Media,
DOI: 10.1557/proc-348-143.
You can read the full text:
Contributors
The following have contributed to this page
