Synthesis And Electrical Properties Of Pb(Ni_1/3Nb_2/3O₃ Based Relaxor Ferroelectric Materials

As a typical relaxor ferroelectric materials,Pb(Ni_1/3Nb_2/3O₃（PNN）has been studied because of its good electrical properties with Curie temperature approximately-120℃.PbTiO₃（PT）is a normal ferroelectric with Curie temperature about 490 ℃.PNN can form binary solid solution with PT,the Curie temperature can be controlled between-120 ℃ and 490 ℃ with different PT content.Pb(Ni_1/3Nb_2/3O₃-PbTiO₃（PNN-PT）is a typical relaxor ferroelectric which shows outstanding dielectric and piezoelectric properties near the morphotropic phase boundary（MPB）region.However,the relatively low Curie temperature of（1-x）PNN-xPT in MPB regions limit its applications in the high-temperature range.In order to increase the Curie temperature,many studies have been investigated.On the other hand,Pb is a problematic toxic chemical that has high risk to human health and environment.There fore,extensive researches have been made to improve the electrical properties of conventional lead-free piezoelectric materials.The newly discovered lead free BaTiO₃-CaTiO₃（BT-CT）have been attracted great attention due to their higher ferroelectric,higher piezoelectric constant and higher electrostrictive strain（0.22%）were obtained near the solubility limit.For example,Liu and Ren reported a high piezoelectric constant（d₃3～620pC/N）in Pb-free piezoelectric ceramic system Ba（Ti0.80Zr0.20）O₃-Ba0.70Ca0.30TiO₃.Therefor,it will be very useful to study Ba0.70Ca0.30TiO₃ which near the solubility limit of BCT ceramics.First,a ternary solid solution system Pb（Lu1/2Nb1/2）O₃-Pb(Ni_1/3Nb_2/3O₃-PbTiO₃（PLN-PNN-PT）has been synthesized by a modified two-step columbite precursor method.The structure,dielectric,ferroelectric and piezoelectric properties characterized by means of X-ray diffraction（XRD）,ferroelectric and dielectric measurements.With the increasing of PT contents,the Curie temperature Tc increases gradually.All samples show excellent piezoelectric properties.The composition of 0.30PLN-0.31PNN-0.39PT exhibits excellent physical properties with d₃3 = 366pC/N,Tc = 214 ℃,Pr = 32.89 μC/cm² and Ec = 15.23 KV/cm.Second,Pb(In_1/2Nb_1/2)-Pb(Ni_1/3Nb_2/3O₃-PbTiO₃（PIN-PNN-PT）ceramics were prepared sucessfully using a modified two-step synthetic process.The phase structure,ferroelectric,dielectric and piezoelectric properties were investigated.The compositions within the morphotropic phase boundary（MPB）region exhibit excellent properties in the ternary system.The composition of 0.30PIN-0.33PNN-0.37PT ceramic was found to have optimal properties with d₃3 = 386 pC/N,Tc = 200 ℃,ε’ ＝2692,kp=50%,tanδ = 0.045,Pr=33.5 μC/cm² and Ec= 16.09 KV/cm at room temperature,respectively.Finally,high quality ferroelectric single crystal PLN-PNN-PT was successfully obtained.The Curie temperature Tc is near 221 ℃ with high piezoelectric coefficient d₃3（800 pC/N）,which is much higher the PLN-PNN-PT ceramics.Third,（1-x）Ba0.7Ca0.3TiO₃-xBiScO₃（BCT-BS）ceramics were prepared using a solid solution state reaction method and characterized by means of X-ray diffraction（XRD）,ferroelectric and dielectric measurements.With increasing of BiScO₃（BS）content,the Curie temperature Tc decreases gradually,which is probably caused by the Bi³⁺substitution for Ba²⁺ site and the decreasing in grain size.