Simulation study of the defect models of Cr-doped PbWO4 crystal and Cr, La-co-doped PbWO4 crystal

The possible defect models of Cr:PbWO4 (PWO) and Cr:La:PWO crystal are proposed and studied by the defect formation energy calculation using the general utility lattice program code (GULP). The calculated results support the proposed models that in lightly doped Cr:PWO crystal, Cr substitutes Pb2+ in the (CrPb3+)+ state forming electrical neutral dipole defect [2(CrPb3+)+–(VPb)2−]. However in heavily doped Cr:PWO crystal or Cr:La:PWO crystal, when the Cr doping level exceeds a certain critical value, Cr occupies W6+ site in the (CrW4+)2− state forming electrical neutral defects [2(CrPb3+)+–(CrW4+)2−], [(LaPb3+)+–(CrPb3+)+–(CrW4+)2−] or [2(LaPb3+)+–(Crw4+)2−]. The appearance of (CrW4+)2− marks a sudden change of the lattice site of the impurity Cr ion and would introduce a sudden change of the physical properties of the crystal and result in a Cr doping level threshold effect existing in the heavily Cr doped PWO crystal and Cr:La:PWO crystal.