Study On The Relaxor Ferroelectrics Ceramics Of Lead Magnesium Niobate

The complex perovskite relaxor ferroelectric ceramics, such as lead magnesium niobate (Pb(Mg_1/3Nb_2/3)O₃ ,abbreviated PMN), have excellent dielectric and ferroelectric properties. The relaxor ferroelectric ceramics have been giving more and more attention in the multilayer ceramic capacitors (MLCC), high voltage high dielectric constant ceramics and other aspects around the world, and they would be investigated intensively.This paper briefly introduced the general situation, the electric properties, applications and preparation of relaxor ferroelectrics. The columbite route was used in the experiment, in order to get the pure powders of PMN-PT-BT, and reduce the formation of pyrochlore phase. The influences of different dopants and preparation conditions on dielectric properties, dissipation and breakdown voltage were studied based on the powders of PMN-PT-BT, and the breakdown and protection of the ceramics are also analysed.In the experiment, MgO, La₂O₃, Yb₂O₃ and SrTiO₃ were used as dopants, and every electric characteristic was measured. All these dopants mentioned above can make Curie peak move to a lower temperature, the dissipation factor larger and the dielectric constant decreased. When doped with 12.5wt% MgO, the ceramics can achieve a breakdown field strength of 5900V/mm. When doped with La₂O₃, the deterioratin of the ceramics changs from descending to ascending. When doped with greater than 2.5wt% Yb₂O₃ in the PMN-PT-BT containing 10wt% MgO, the dielectric constant decreases more slowly, When doped with SrTiO₃, the ceramics could be sintered at low temperature below 1100℃.This paper analyzes the craft conditions of the ceramics, such as adhesive dosage, pressure force size, speed of the warming-up and so on. Considered experimental conditions and equipment limitations, the amount of 10wt% adhesive dosage, a two-way same time compression, 12Mpa pressure size and heating rate of 300℃per hour are applied. In the experiment of pressure testing, vancant margin of the wafer surface of electrode could increase the length of the discharge and discharge voltage. And the margin with insulating coating could prevent surface discharge better, and improve the withstand voltage of the ceramics.