Growth And Characterization Of Transition Metal Element Doped Ferroelectric Crystals

(1-x)Pb(Mg_1/3Nb_2/3)O₃-x Pb Ti O₃?PMN-x PT?relaxation ferroelectric single crystal is an important functional material.This novel ferroelectric material exhibits excellent electrical properties at its Morphotropic Phase Boundary?MPB?,including dielectric,piezoelectric,ferroelectric,pyroelectric,electromechanical coupling,and field-induced strain,when compared with traditional ferroelectrics.Therefor,to make full use of its advantage,the material is applied widely in the preparation of pyroelectric detectors,drivers,high-definition medical imaging equipment and other fields.However,PMN-x PT single crystal has the problems of low phase transition temperature and small coercive field,which limit its use in high temperature and high power environment.In addition,as the device gradually becomes smaller and more versatile,single-phase multiferroics materials with the coexistence of ferroelectricity and magnetic properties has become a hot spot in research.PMN-x PT single crystal is a typical ferroelectric material,whereas single ferroelectricity limits its freedom in device design.The core work of this dissertation is to improve the Curie temperature and coercive field of PMN-32PT single crystal by doping the transition metal ions such as Co³⁺,Cu²⁺,and Fe³⁺.Meanwhile,the influence of transition metal elements on the magnetic properties of PMN-32PT single crystal was explored,thus to realize the coexistence of ferroelectricity and ferromagnetism at room temperature.PMN-32PT:Co,PMN-32PT:Cu and PMN-32PT:Fe single crystals are produced by the flux method.The XRD results show that the grown single crystals make a pure perovskite structure.After the transition metal ions are doped with PMN-32PT,the single crystal diffraction peaks are shifted to a larger angle and the lattice size becomes smaller.SEM images show that the crystals are grown in steps.The results of the research on the electrical properties show that the addition of Co³⁺,Cu²⁺,and Fe³⁺ions improves the electrical properties of PMN-32PT single crystals.The coercive field is increased to 8.2 k V/cm,6.6 k V/cm and 10.5 k V/cm,and the tripartite-tetragonal phase transition temperature is raised to 107?,120?and 130?,respectively.The fitting conclusion of Curie-Weiss law,modified Curie-Weiss law and Lorentz formula indicate that the dielectric relaxation characteristics of PMN-32PT single crystals doped with transition metal ions are significantly improved.It is related to changing the polar domain of PMN-32PT single crystal ferroelectric domain.Research on the magnetodielectric coupling properties of single crystals found that PMN-32PT:Co,PMN-32PT:Cu and PMN-32PT:Fe single crystals have negative magnetoelectric coupling effects in small magnetic fields at room temperature.The coupling effect will raise as the strength of the magnetic field increases.Under the 1.2 T magnetic field,the magnetodielectric coupling coefficient reaches-1.37%to-2.52%.Compared with the magnetic dielectric effect of other magnetodielectric composite materials,the single crystals that we prepared have obtained excellent magnetic dielectric effects.