Computer modelling techniques based upon energy minimisation were used to study the defect chemistry of this scintillator phase. A potential set was derived by fitting the present structure, together with Bi12GeO20, and this potential set was then used to calculate the bulk properties of Bi4Ge3O12 and Bi12GeO20. The formation energies of intrinsic defects, and non-stoichiometry, were studied. Charge transport mechanisms were compared with experimental results obtained using impedance spectroscopy. The potential parameter-set reproduced the lattice parameters of the 4-3-12 and 12-1-20 phases to within 0.3%. The main intrinsic disorder in the 4-3-12 phase was predicted to be the Bi/Ge antisite. Impedance spectroscopy measurements of the Bi4Ge3O12 phase were also carried out, and the results indicated that the charge transport mechanism could be related to a process with a distribution in activation energies; with a mean value of about 1.41eV.

Modelling Intrinsic Defects and Transport Mechanisms in the Bismuth Germanate Crystalline System. M.E.G.Valerio, R.A.Jackson, Z.S.Macedo: Physica Status Solidi C, 2005, 2[1], 485-9