The Microstructure And Electrical Properties Of PMN-PZN-PZT Ceramics

Pb(Mn₁/3Nb₂/3)O₃-Pb(Zn₁/3Nb₂/3)O₃-PbTiO₃-PbZrO₃(PMN-PZN-PZT for short) quaternary piezoelectric ceramics were prepared by the solid-state reaction. The effect of calcining temperature, PMN content and Sr, SiO₂ dopants on the microstructure and electrical properties were investigated systematically. The main contents of this paper were listed as follows:The PMN-PZN-PZT ceramics were calcined at 850°C and 900°C. The experimental results were shown as follows: the powder calcined at 900°C had less pyrochlore phase than that calcined at 850°C, which suggested that the higher temperature leads to the homogeneous distribution; the 1200°C sintered samples calcined at 900°C had no pyrochlore phase whereas the sample with 12.5mol%PMN calcined at 850°C had a little pyrochlore phase; calculating results of lattice constant revealed that the lattice constants of 900°C samples is larger than 850°C samples; comparing the electrical properties of the samples calcined at 900°C and 850°C, we found that the former is the better.Fixed ratio as 2:8 between PMN-PZN and PZT, the effect of the variation of PMN content on the microstructure and electrical properties were investigated. It was found that the phase structure changed from tetragonal to rhombohedral and the morphotropic phase boundary was at the compositon of 6mol% PMN, where the electrical properties varied sharply, dielectric constant (ε33^T/ε0), piezoelectric constant(d₃3), dielectric loss(tanδ) and electromechanical factor(k_p) had arrived the maximum value but mechanical quality factor(Q_m) decreased up to the minimal value. With the increase of PMN content, ε33^T/ε0 and d₃3 decreased while Q_m increased because PMN is a kind of "hard" piezoelectric ceramics. The stability of Mn ion in the oxygen octahedron is lower than Zn ion because of a weaker Mn-0 binding energy in contrast with Zn-O, which leads to the lower curie temperature(T_c) of PMN. With the increase of PMN content, the T_c of this system decreased.In order to improve the electrical properties, Sr ion was added into the quaternary systems. Crystal was distorted because of smaller radius of Sr²+, which caused the phase structure changed from rhombohedral to tetragonal. With the increase of Sr content, ε33^T/ε0 , k_p and d₃3 increased and Q_m was decreased.On the basis of the foregoing composition with high quality, SiO₂ was added. It was found that in the initial stage of sintering SiO₂ played the role of flux, which resulted in the decrease of sintering temperature. In the final stage of sintering, SiO₂ entered the crystal lattice and improved the electrical properties. When the content of SiO-2 was 0.05wt%, ε33^T/ε0, d₃3 and tanδ reached the maximum. When the content was 0.1wt%, k_p reached the maximum and Q_m reached minimum. With the increase of SiO₂, amorphous phase appeared and the electrical properties were deteriorated.