Growth Of Layered Perovskite Bi_4-xNd_xTi₃O₁₂ Ferroelectric Single Crystal Research On Dynamical Scale With Loops

Ferroelectrics Bi4Ti3O12 of layered perovskite has large spontaneous polarization Ps which is close to the a-axis and high Curie temperature.However,Bi4Ti3O12 thin films suffer from polarization-switching fatigue on metal electrode and this problem hampers its application for nonvolatile memories.It was found that part substitution of Bi with rare-earth-elements shows a high fatigue endurance on metal electrode.Rare-earth-element substituted Bi4Ti3O12 ferroelectrics are one of the best materials to realize the application of ferroelectric memories.In order to clearly understand the effect of part substitution of Bi with rare-earth-elements on the fatigue characteristics,it is necessary to compare the crystal structure,ferroelectric properties,domain structure and domain boundary dynamics of pure Bi4Ti3O12 and rare-earth partially substituted Bi4Ti3O12 single crystals.Nevertheless,there is a few reports on this topic in the literature,because it is difficult to obtain thicker bulk single crystals,although it is easy to grow small and thin single-crystal slices of layered perovskite.As we know,layered perovskite oxides grow very slowly along the c-axis compared to its rapid growth along the a-b plane.We synthesized superfine Bi4-x Ndx Ti3O12(BNd T,x=0,0.5,0.8)powders through a sol-gel process and then grew bulk BNd T single crystals by using the self-flux method.In this paper,both the synthesis of superfine powders and the growth condition of single crystals are presented,and then the influence of Nd-substitution content on the ferroelectricity,dielectric properties and leakage current of BNd T single crystals is discussed.Finally,the effect of Nd-substitution content on the dynamic hysteresis scaling behaviors of BNd T single crystal is studied.The main results and conclusions are as follows:1.Large ferroelectric BNd T single-crystal plates of layered perovskite were grown from the ultrafine powders synthesized through a sol-gel process by using the self-flux method with Bi2O3 as a flux.Among them,1.14 mm thick Bi4Ti3O12 single crystals have a diameter of 4.7 cm.Such a large Bi4Ti3O12 single-crystal plate has never been reported before.The rocking curves of the Bi4Ti3O12 single crystal surface were wide and the peak shape was asymmetric,which indicates that the crystal was incomplete and there must be a small angle grain boundary.2.The ferroelectric and dielectric properties as well as the leakage current of BNd T single crystals were measured when the electrical field was applied along the a/b axis.The ferroelectric properties and the leakage current of BNd T single crystals were measured when the electrical field was applied along the c axis at room temperature.The results show that the Pr value of Bi4Ti3O12 single crystal along the a/b axis is about 48.1 mC/cm.With increasing Nd content,the Pr value of the single crystals decreases,both their dielectric constant and dielectric loss decrease,and their leakage current decreases due to decrease in the oxygen vacancy concentration.3.At room temperature,the dynamic hysteresis scaling power-law relations of BNd T(x=0,0.5,0.8)single crystals can be expressed by <A>?f-0.1746Eo2.8933,<A>? f-0.1982Eo2.7675 and <A>?f-0.2134E02.6432,respectively.This fact indicates that the f dependences of polarization reversal in BNd T single crystals increases with increasing Nd-doping content,and the dependence on E0 decreases gradually.