The phase stabilities and piezoelectric properties of morphotropic phase boundary ternary piezoceramics (0.2Pb(Mg1/3Nb2/3)O-3-0.38PbZrO(3)-0.42PbTiO(3)) are investigated as a function of sintering conditions. The tetragonality (c/a) of the morphotropic phase boundary, where the rhombohedral and tetragonal phases coexist (space groups R3m and P4mm, respectively), is affected by the sintering temperature and time. This tetragonality affects the piezoelectric properties. The results demonstrate that a large tetragonality is undesirable for the piezoelectric properties. The structure and properties of morphotropic phase boundary piezoelectric materials are strongly correlated.