Morphotropic phase boundaries in the Pb(Sc/sub 1/2/Nb/sub 1/2/)O/sub 3/-Pb/sub 1-x/La/sub x/Ti/sub 1-x/4/O/sub 3/ system

Lead zirconate titanate ceramics and their solid solutions with several lead-based relaxor perovskite ferroelectric oxides represented by Pb(B/sub 1/,B/sub 2/)O/sub 3/ are of considerable interest, because a morphotropic phase boundary (MPB) separating the rhombohedral and tetragonal phases exists in their system. A material with the MPB composition is expected to show an enhanced good properties. In this study, morphotropic phase boundary compositions in the PSN-Pb/sub 1-x/La/sub x/Ti/sub 1-x/4/O/sub 3/(100x) ceramics were investigated. Those ceramics were prepared by the Hot Isostatic Pressing (HIP) after conventional sintering in the PbO-rich atmosphere. In the PSN-PT(x=0) solid solution system, the MPB exists at the composition close to 42.5 mol% of PT. The MPB also exists at around 42 mol% of PLT (x=0.15) in the PSN-PLT(15) system. Dielectric constants increase with increasing La concentrations. On the other hand, coupling coefficients somewhat decrease with increasing La compositions. For examples, dielectric constants and coupling coefficients were 2800, and k/sub p/=0.7 and k/sub t/=0.5 for the 0.58PSN-0.42PT(x=0), respectively. On the other hand, those were 4500, and k/sub p/=0.6 and k/sub t/=0.55 for 0.58PSN-0.42PLT(15), respectively. Therefore, the PSN-PLT system may show the maximum piezoelectric constants d's at the appropriate La composition of MPB.