Synthesis And Electrical Properties Of Bi_0.5Na_0.5TiO₃-Based Lead-Free Piezoceramics

Bi_0.5Na_0.5TiO₃?BNT?piezoelectric material is one of the hot-spots for the current lead-free piezoelectric material research because of its excellent electrical performance.Similar to PZT lead-based material,BNT can be dissolved with other perovskite structure materials to form solid solution with morphotropic phase boundary?MPB?.In this paper,BNT ceramics of 0.975BNT-0.025BC and0.93BNT-0.07BT ceramics with MPB were prepared by solid solution of BNT ceramics made of BiCoO₃ and BaTiO₃ materials with excellent performance.Among them,0.93BNT-0.07BT ceramics have obvious advantages on ferroelectric and piezoelectric properties,the remanent polarization intensity P_r,coercive field E_c,piezoelectric constant d₃₃ are 30.6?C/cm²,16.91kV/cm,150pC/N respectively.Based on the former solid solution study of Bi_0.5Na_0.5TiO₃ ceramics,0.93BNT-0.07BT ceramics was selected as the matrix material to ion of different valence states doping modification for its better performance.The phase structure,ferroelectric properties and piezoelectric properties of 0.93BNT-0.07BT ceramics doped with La³⁺,Mn⁴⁺and Mo⁶⁺by their different valence states were characterized respectively.And the effect of different valence ion doping on ceramic properties was analyzed.It's found that the doping of La³⁺weakens the ferroelectric properties of ceramics.The anti-ferroelectric characteristics become more obvious with the increase of doping amount.The remanent polarization intensity and coercivity field of 0.93BNT-0.07BT ceramics were decreased by Mn⁴⁺doping,but the piezoelectric properties of the ceramic samples were slightly improved due to the reduction of coercivity field and the low doping content.Mo⁶⁺in MoO₃ doped ceramics is easy to be reduced to Mo ions with low valent state during high-temperature sintering,which result in excess oxygen vacancy in the lattice.The concentration of oxygen vacancy strengthens the"pinning"effect of domain wall,and the coercivity field increases,thus improving the stability of ferroelectric properties.Compared to other dopants,MoO₃ doped 0.93BNT-0.07BT ceramics has better ferroelectric properties,and the remanent polarization intensity increases with increasing doping amount,which indicates that the homogeneity of the domain orientation is high-level,thus the piezoelectric properties are better.Therefore,it is necessary to further study the electrical properties of MoO₃ doped 0.93BNT-0.07BT ceramics,including piezoelectric properties,dielectric properties,leakage characteristics and energy storage characteristics.It is found that the piezoelectric properties of the ceramic are excellent at the doping amount x=0.10 of MoO₃.Then MoO₃ will strengthen the short-range order of the domain,and the stronger the relaxation of the ceramic will be as the amount of doping increases.Through the analysis of the leakage characteristics,it is found that the leakage current changes little before and after doping,and the enhancement of the piezoelectric properties of ceramics is caused by the change of lattice structure.At the same time,the doping of Mo⁶⁺can improve the energy storage efficiency of ceramics to a certain extent.When the molar ratio of doping is 0.10,the energy storage efficiency is greatly0.593%.