During holographic recording in lead germanate (Pb5Ge3O11) crystals two types of refractive-index gratings are observed. One has a very fast response whereas the second builds up comparably slowly. Measurements of diffraction efficiency and two-beam coupling are carded out to study the formation of both gratings and to obtain the relative phase between them. Differently doped and thermally treated samples are divided into four classes due to their different time evolution of diffraction efficiency and of the energy transfer direction during two-beam coupling. The classification depends on doping and treatment. For Ni-doped and thermally treated samples dark and photo conductivities corresponding to the slow grating are determined, indicating that Ni-doping combined with oxidation enhances the properties of the slow grating.