The Research On Tape-casting Processing And Properties Of Textured KNN-based Lead-free Piezoelectric Ceramics

For piezoelectric ceramics, the most widely-used now is the traditional PbZrTiO3 system in the world. These materials exhibit very high piezoelectric properties. However, they contain poisonous substance PbO with a high proportion reaching 70%.So it is an important project to develop a new lead-free material to substitute the PZT-based piezoelectric ceramic in the research field.(K0.5Na0.5)Nb03-based piezoelectric ceramics has been being paid attention to increasingly by the use of electro-optic materials these years, because its high Curie Temperature, hige piezoelectric properties and environmental harmony. However, its electric properties are limited due to the difficulty in obtaining dense KNN-based ceramics. This study tries to improve the electric properties by combining three methods:the substitution of ABO3-type compounds, the use of sintering aids and textured processing.Firstly, the technological parameters of tape-casting processing have been searched. KNN-based textured ceramics is prepared by TGG technique. The contents of organic solvents,dispersant,plasticity agent and binder have been determined by orthogonal design and the uniform,diversified,moderate viscosity slurries are obtained as well as the high quality green tape. The effect of gap height and carrier speed on the texture degrees are studied. It is good that gap height is 150μm and carrier speed is 1.0cm/s.Secondly, the textured KNN-0.015BiScO3 is prepared by TGG and the effect of the contents of the templates on the structure and electric properties are mainly studied. Compared to random-oriented ceramics, the Curie Temperature of the textured ceramics has not decreased and these has more stable dielectric constants. In the 100～300℃, the rate of change ofε-T is 20% for random-oriented ceramics, and 7% for textured ones. Besides that, both the ferroelectric and piezoelectric properties have been improved. Especially when the content of templates is 10%mo, Pr is enhanced to 34.1μC/cm2, d33- coefficients reach 202pC/N, kp is 0.38.Finally, the effect of Fe2O3 on the structure and electric properties are studied. As a sintered aid, it is effective to lower the sintered temperature of KNN-0.015BS(it reduced 40℃in this experiment). By adding Fe2O3,the density has been improved and the maximum reaches 4.659g/cm3 when the content of Fe2O3 is 1%mol.