A phase diagram based on dielectric-permittivity-versus-temperature measurements and high-temperature X-ray diffractometry was proposed for 0.4Pb(Ni-1/3,Nb-1/3) O-3-xPbZrO(3)-(0.6-x)PbTiO3, (0.2 less than or equal to x less than or equal to 0.32) relaxor-ferroelectric solid solution, and a morphotropic phase boundary that sharply bends toward zirconium-rich compositions was found. A spontaneous normal-to-relaxer ferroelectric transition was also observed when heating was performed for all the compositions tested near the morphotropic phase boundary. Additional considerations about previously published phase diagrams for Pb(Zn-1/3,Nb-2/3)O-3-PbTiO3 and Pb(Mg-1/3,Nb-1/3)O-3-PbTiO3 might lead to an extension of the presented diagram to these compositions.