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Abstract
TlBr is promising for g- and x- radiation detection, but suffers from rapid performance degradation under the operating external electric fields. To enable molecular dynamics (MD) studies of this degradation, we have developed a Stillinger-Weber type of TlBr interatomic potential. During this process, we have also addressed two problems of wider interests. First, the conventional Stillinger-Weber potential format is only applicable for tetrahedral structures (e.g., diamond-cubic, zinc-blende, or wurtzite). Here we have modified the analytical functions of the Stillinger-Weber potential so that it can now be used for other crystal structures. Second, past modifications of interatomic potentials cannot always be applied by a broad community because any new analytical functions of the potential would require corresponding changes in the molecular dynamics codes. Here we have developed a polymorphic potential model that simultaneously incorporates Stillinger-Weber, Tersoff, embedded-atom method, and any variations (i.e., modified functions) of these potentials. We have implemented this polymorphic model in MD code LAMMPS, and demonstrated that our TlBr potential enables stable MD simulations under external electric fields.
Highlights
Thallium bromide (TlBr) has emerged to be one of the most promising semiconductors for γ- and x- radiation detection in recent years, achieving resolution as high as 1% at 662 keV (Shorohov et al, 2009; Hitomi, Matsumoto, Muroi, Shoji, & Hiratate, 2002)
As ionic conduction may be affected by defective structures such as the open channels of edge dislocations, molecular dynamics (MD) that allows extended defects to be included in simulated crystals becomes a useful method to study the ionic conduction induced structure evolution of TlBr
Our objective is to study the equilibrium TlBr crystal under the stoichiometric condition where no other phases occur, so that the critical properties are for the TlBr-captures the crystalline growth of the equilibrium (CsCl) crystal
Summary
Thallium bromide (TlBr) has emerged to be one of the most promising semiconductors for γ- and x- radiation detection in recent years, achieving resolution as high as 1% at 662 keV (Shorohov et al, 2009; Hitomi, Matsumoto, Muroi, Shoji, & Hiratate, 2002). To collect the charges created during the radiation events, the material must be subject to an external electric field. The performance of TlBr degrades under external electric fields after operation times as short as a few hours to a few weeks (Hitomi, Kikuchi, Shoji, & Ishii, 2009). It is unclear if this degradation comes from the structure evolution due to the ionic conduction under the electric fields. Such MD simulations are not yet possible due to the lack of an interatomic potential for the Tl-Br system that has a CsCl type of crystal structure
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