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 ?C/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 ?,?' ?2692,kp=50%,tan? = 0.045,Pr=33.5 ?C/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.