Pb-containing relaxor ferroelectric ceramics are prepared by mechanochemical ceramic processing. Mechanochemical reactions in binary and ternary mixtures of the PbO-ZnO-Nb₂O₅ system are studied by x-ray diffraction. Disordered compounds with the columbite, changbaiite, and pyrochlore structures are prepared. The perovskite and pyrochlore phases in 0.9Pb(Zn_1/3Nb_2/3)O₃ + 0.1ABO₃ morphotropic phase boundary materials are shown to be in mechanochemical equilibrium. Among the ABO₃ additives studied, BaMnO₃ is the most effective for stabilizing the perovskite structure. The mechanochemical synthesis path has a strong effect on the phase composition of the resulting material. Conventional synthesis through a columbite phase leads to the predominant formation of a pyrochlore phase. Firing conditions also have a profound effect on the phase composition of the ceramics, but the disordered perovskite phase retains cubic symmetry.