Morphotropic phase boundaries in the Pb(Sc1/2Nb1/2 )O3-Pb1-xLaxTi1-x/4O 3 system

Lead zirconate titanate ceramics and their solid solutions with several lead-based relaxor perovskite ferroelectric oxides represented by Pb(B₁,B₂)O₃ 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_1-xLa_xTi_1-x/4O₃(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_p=0.7 and k_t=0.5 for the 0.58PSN-0.42PT(x=0), respectively. On the other hand, those were 4500, and k_p=0.6 and k_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