| Ceramic dielectric capacitors are devices that physically store and release electrical energy,with the advantages of high power density,safety and reliability and fast charging and discharging rate,and well adapted to the development trend of miniaturization,light weight and integration of energy storage devices,they have attracted wide attention.However,the continuous supply of electrical energy requires the development of ceramic dielectric materials with high energy storage density.Lead-free perovskite relaxor ferroelectric ceramics are excellent candidates for creating eco-friendly dielectrics with high energy storage density,which can be fabricated by adding new end-members to normal ferroelectric materials.Recently,the role of configurational entropy in the composition design and performance regulation of advanced ceramics has received increasing attention,leading to the development of high-entropy ceramics.With the aim of achieving high energy storage performance,this paper has conducted research on the composition design and preparation of highentropy relaxor ferroelectric ceramics.Firstly,the compositions at morphotropic phase boundary of 0.82Bi0.5Na0.5TiO30.1 8Bi0.5K0.5TiO3 and 0.8525Bi0.5Na0.5TiO3-0.10995Bi0.5K0.5TiO3-0.03755BaTiO3 were chemically modified by Sr(Mg1/3Nb2/3)O3(SMN)to prepare a series of bismuth sodium titanate-based relaxor ferroelectric ceramics.The phase structures,microstructures,dielectric properties,and energy storage properties of the two ceramic series were also investigated.Two kinds of high-entropy ceramics with SMN content of 15 mol%have energy storage density(Wrec)over 3 J/cm3 and energy storage efficiency(η)over 85%at moderate electric field(approximately 300 kV/cm).These ceramics also demonstrate good thermal stability and frequency insensitivity,providing strong competitive advantages at moderate electric field.Secondly,a design method of high-entropy relaxor ferroelectric energy storage ceramics based on the medium-entropy ferroelectric ceramics combined with other perovskite end-members is proposed in this paper.That is to introduce end members Sr(Mg1/3Nb2/3)O3 or Sr(Mg1/3Ta2/3)O3(SMT)into(Bi0.4Na0.2K0.2Ba0.2)TiO3 mediumentropy ceramics to increase its configurational entropy and optimize its energy storage performance,respectively.The ceramic samples show a single perovskite structure,with a dense microstructure and the average grain size of less than 1 μm.A variety of different ions introduced using a high-entropy strategy can break the long-range ferroelectric order and optimized the polarization configuration,among which the high-entropy relaxor ceramics with the content of 12 mol%SMN and 12 mol%SMT show the best energy storage performance,the Wrec of both ceramics exceeds 3 J/cm3,while the η exceeds 80%.And the energy storage performance of the two highentropy ceramics has low sensitivity to temperature and frequency.The above results provide a reference for the design of high-entropy relaxor ferroelectric ceramics with high energy storage performance.In addition,for the low energy storage efficiency of 0.88(Bi0.4Na0.2K0.2Ba0.2)TiO3-0.1 2Sr(Mg1/3Nb2/3)O3 high-entropy relaxor ferroelectric ceramics,15 mol%Zr4+was used to partially substitute Ti4+,which successfully increased the η to over 90%,and the Wrec of ceramics is 3.68 J/cm3.Finally,a strategy of modifying ferroelectric ceramic matrix with medium entropy perovskite oxide is proposed to enhance the energy storage performance.The(Bi0.4Na0.2K0.2Ba0.2)TiO3 medium-entropy and(Bi0.4Na0.2K0.2Ba0.2)Ti0.95Zr0.05O3 highentropy ceramics were modified by the medium entropy perovskite oxide end-member Sr(Mg1/3Nb1/3Ta1/3)O3(SMNT),respectively.And the phase structure,microstructure,dielectric properties and energy storage properties of the two high-entropy ceramic systems were studied at the same time.With a low content of SMNT,the ceramics in the high-entropy range,and the relaxation of the ceramics is significantly enhanced.The Wrec and η of the 0.92(Bi0.4Na0.2K0.2Ba0.2)TiO3-0.08Sr(Mg1/3Nb1/3Ta1/3)O3 high-entropy ceramics under the electric field of 275 kV/cm are 3.22 J/cm3 and 86.3%,respectively.For the 0.91(Bi0.4Na0.2K0.2Ba0.2)Ti0.95Zr0.05O3-0.09Sr(Mg1/3Nb1/3Ta1/3)O3 high-entropy ceramics,the recoverable energy densnty of 3.83 J/cm3 and the energy storage efficiency of 85.7%can be achieved under an electric field of 360 kV/cm.This paper makes a preliminary exploration on the high-entropy enhanced dielectric energy storage performance.With high configurational entropy,the equivalent lattice sites can accommodate a variety of ions with different valence states,ionic radii and properties,which have an important impact on the polarization configuration and relaxation of ceramics.The results show that it is an effective method to regulate energy storage performance by introducing end-members to adjust the relaxation through the high-entropy strategy. |
PDF Full Text Request