Properties And Modulation Of Colossal Dielectric Materials Based On Iron And Manganese Elements

The application of dielectric materials in life is everywhere which is indispensable for the development of science and technology.The conversion among mechanical,thermal,acoustic,and optical properties,as well as the storage of energy,has extremely important usage in the fields of national defense,detection,communications and energy.As the improvement of science and technology,these inevitable trends of high energy density,high degree of integration,and device miniaturization have driven a large number of scientific research workers to carry out research on giant-dielectric or even colossal dielectric materials.Especially,with the recent development of the electric vehicle industry,battery with high energy storage density has become a research hotspot and the improvement of the performance of dielectric materials is an important factor in the innovation of energy storage technology.Therefore,this paper will work on the preparation and dielectric properties of several colossal dielectric materials to study their dielectric physical mechanism and dielectric modulation mechanisms.Based on Internal Barrier Layer Capacitance?IBLC?effect,we prepared(Fe_0.5Li_0.5)_x Zn_1-x-x O ceramics to research on their colossal dielectric property.The dielectric anomalies such as dielectric steps are analyzed.The role and i nfluence of Fe and Li elements in co-doped ceramic samples were studied;and the effect of co-doping with different doping concentrations was studied.Another common valence element,Mn,is introduced to build colossal dielectric materials.Sr_1-x-x Ba_x Mn O₃ ceramics are prepared.The temperature profile of the dielectric properties of the material was measured and the dielectric relaxation at the dielectric step was measured.The analysis was carried out to study the physical mechanism of the colossal dielectric property,then the microwave electromagnetic parameters of the Sr_1-x-x Ba_x Mn O₃ sample were measured.Two kinds of mix-valent elements have been introduced into two different materials,respectively.And the materials show colossal dielectric property which suggests that the rountine of creating colossal dielectric materials by introducing mix-valent elements is a universal way.To further confire that idea,i t was decided to introduce both Fe and Mn valence elements to study the influence of these two elements on the dielectric properties and the interaction between them.Thus,?1–x?(Ca_0.6Sr_0.4)_1.15Tb_1.85Fe₂O₇-x Ca₃Mn₂O₇ ceramics were prepared.It was found that the doping of Mn element makes the dielectric curve change from a step to two steps,and the height of the dielectric platform increases by two orders of magnitude.The introduction of Fe,Mn element can provide more free charges and charge-hopping lattice sites make the grain and grain boundary conduction change faster and bigger,showing a steeper dielectric step and a higher dielectric plateau.Sample 0.1-CMO shows wide dielectric plateau??_r?>1.7×10⁵ at the frequency of 1 kHz in range of 289–583 K?.Unlike the colossal dielectric materials based on space charges,proper low doping in perovskite ferroelectrics will contribute to the localizing of free charges within the unit cell scale forming polarons.Thus,we have grown 0.01at%Fe:K_0.95Li_0.05Ta_1-x-x Nb_x O₃ single crystals to investigate the interaction between polarons and ferroelectric polarization lattices.The dielectric anomalies in the 20 K–200K temperature range were described and the origins were studied.For the temperature range of 200K–450K,we think there are two dielectric anomalies.One is the first-order phase change P1,and the other is a diffuse phase change P2.The interaction between P1 and P2 are not simple linear superposition but promoting each other.The dielectric property can simply be controlled by changing the composition parameter x.This tunable dielectric mechanism provides a way to design new types of optimized dielectric materials.The 0.01at%Fe:K_0.95Li_0.05Ta_0.57Nb_0.43O₃ single crystal have high thermal stability and low dielectric loss??_r?>5000 and tan?<0.025 at 1k Hz in range of 304–377 K?.Based on polarons,we use a new model assumption to describe the dielectric phenomena of the sample.