| The relaxor ferroelectrics (1-x) Pb(Mg1/3Nb2/3)O3-xPbTiO3(PMN-PT) prohibit excellent piezoelectric, dielectric and electro-optic properties, which make them promising candidate materials for applications in piezoelectric actuator, multi-layer ceramic capacitors, electro-optical devices and so forth. Chemical powders (Nb2O5, MgO, PbO, TiO2) were used as starting materials, and0.67PMN-0.33PT powders were synthesized using the two-step columbite precursor technique. Then PMN-PT ceramics were prepared through hot-pressing and normal sintering process by using these powders. We investigated the effects of excess Pb, sintering temperature, and sintering time on the PMN-PT ceramic structure and properties. In addition, we stimulated the effects of residual pores and grain boundaries on the transmission through PMN-PT ceramics with Matlab software. Translucent La-doped PMN-PT ceramics are prepared by hot-pressed sintering, and their structure characteristic and properties were investigated.The appropriate Pb excess is beneficial to improve properties of PMN-PT ceramics, and PMN-PT ceramics with1%excess of PbO achieve their best in ferroelectric, dielectric and piezoelectric properties. The properties of hot-pressing PMN-PT ceramics are apparently better than those of normal sintering samples, for example, their piezoelectric coefficients d33and electromechanical coupling coefficients kp are660pC/N,71%and600pC/N,61%respectively. The decrease in density and worsening in properties of PMN-PT ceramics happened when too much excess PbO was added. The hot-pressing PMN-PT ceramics achieve relatively high density when the sintering temperature is low (1150℃), while the normal sintering samples are starting their sintering process at about1210℃. The density and properties of hot-pressing samples are improved with increase of the sintering time, the piezoelectric coefficient d33～680pC/N and remanent polarization Pr～40μC/cm2are achieved when the sintering time is8h.The effects of the residual pores and grain boundaries on the transmission through0.65PMN-0.35PT electro-optic ceramics were studied with Mie scattering theory and the Raleigh-Gans-Debye model. Results show that both in-line transmission and total forward transmission decrease prominently with the increase of the porosity, while the transmission first decrease and then increase along with the increase of the pore size. The minimum of in-line transmission is achieved when the pore size is close to the wavelength of the incident light. Because of the optical birefringence at the grain boundaries, the in-line transmission decreases mono-tonically with the increase of grain size, and the total forward transmission is less sensible to the grain size.Translucent La-doped PMN-PT ceramics are prepared by hot-pressed sintering, and the transparency is about30%for infrared wavelength when its thickness is0.5mm. In addition, La doped PMN-PT ceramics have good ferroelectric properties and low leakage density. |
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