Multiple phase gratings are written in pure, Yb- and P-doped Pb5Ge3O11 crystals: a fast grating and a slow grating with substantially different response times compensate each other. Doping and thermal treatments have strong influences on the behavior of both gratings. Reduction treatments of Yb-doped samples lead to a significant decrease of the response time of the slow grating, while that of the fast grating is diminished by more than two orders of magnitude. P doping significantly increases the response time of the fast grating. Possible origins of both gratings are discussed. © 1999 American Institute of Physics.