| The electrocaloric effect is a physical effect that electric-field-induced entropy change of a polar material gives rise to heat absorption or release,which can be used to realize heat transport and refrigeration.Compared with the currently used compression refrigerators,the solid-state refrigerator based on the principle of electrocaloric effect does not use Freon refrigerants that are harmful to the atmospheric environment,and has the advantages of green and environmental protection.In addition,the electrocaloric cooler is small in size and light in weight,and can be integrated on a circuit board,providing a solution to the heat dissipation problem of IC chips and electronic components.The system and component design of ferroelectric materials is very critical to realize the large electrocaloric effect.The(Pb,La)(Zr,Sn,Ti)O3(PLZST)material system is easy to obtain multiple phase structures and different electrical properties through component control.For this reason,this paper selects PLZST-based ceramics as the research object,and studies the influence of three different methods of composition control,element doping and glass phase addition on its dielectric,ferroelectric properties and electrocaloric effect,and improves the electrocaloric cooling performance of the system.First,this paper studies the influence of the zirconium-titanium ratio adjustment on the electrocaloric effect of(Pb0.94La0.04)(ZrxSn0.30Ti0.70-x)O3(x=0.54,0.52,0.50,0.48)ceramics.It was found that different ratios of zirconium to titanium have a significant effect on the stability of the antiferroelectric phase and the ferroelectric phase.Under an external electric field of 70kV·cm-1,(Pb0.94La0.04)(Zr0.52Sn0.30Ti0.18)O3 antiferroelectric ceramics with a zirconium-titanium ratio of 52/18 have the greatest electrocaloric effect at room temperature:including the isothermal entropy change(?S)of 1.75 J·K-1·kg-1,the isothermal heat(Q)of 0.530 k J·kg-1 and the adiabatic temperature change(?T)of 1.04 K.At 140°C,the(Pb0.94La0.04)(Zr0.50Sn0.30Ti0.20)O3 with a zirconium-titanium ratio of 50/20 has the largest electrocaloric effect,?S and Q are 2.19 J·K-1·kg-1,0.900 k J·kg-1,respectively.Secondly,the relationship between the electrocaloric effect of ferroelectric material and ambient temperature(electrocaloric response)is closely related to its depolarization transition and the phase change behavior from ferroelectric state to paraelectric state.Considering that the large electrocaloric effect often appears at phase transition temperature and Sr element can significantly affect the phase transition temperature of the PLZST system,the influence of Sr2+doping on the electrocaloric effect of PLZST ceramic is studied in this paper.It was found that the antiferroelectricity of(Pb0.92Sr0.02La0.04)(Zr0.48Sn0.30Ti0.22)O3 ceramic doped with 2%Sr2+was enhanced and the depolarization transition temperature(Td)is reduced from 59.5?when undoped to around room temperature,and the electrocaloric effect under an external electric field of 50 kV·cm-1 will peak at 35?(?S=2.20 J·K-1·kg-1,Q=0.677 k J·kg-1,?T=1.36 K).In(Pb0.81Sr0.13La0.04)(Zr0.33Sn0.30Ti0.37)O3 relaxor ferroelectric ceramics doped with 13%Sr2+,the Curie peak is moved to 34.3?,and the electrocaloric effect(external electric field 50 kV·cm-1)became largest at 44?(?S=0.89 J·K-1·kg-1,Q=0.280 k J·kg-1,?T=0.56 K).Studies have shown that Sr2+can reduce the working environment temperature corresponding to the peaks of electrocaloric response of PLZST ceramics,which is beneficial to meet the daily refrigeration needs.Finally,in view of the fact that the induction of the large electrocaloric effect in the ceramic system usually requires the application of high working voltage and higher breakdown electric field of the material,this paper studies the effect of additional 0.5Pb O-0.25B2O3-0.25Si O2 glass on electrocaloric effect of(Pb0.92Sr0.02La0.04)(Zr0.48Sn0.30Ti0.22)O3 ceramic.It was found that PLZST ceramics achieved high-temperature liquid phase sintering after adding an appropriate amount of glass and the breakdown electric field was significantly improved,and it was able to work safely under higher applied electric fields and achieve greater saturation polarization.The maximum values of?S and?T of the ceramic sample with 1%glass added under an electric field of 102.2 kV·cm-1 are 2.28 J·K-1·kg-1 and 2.30 K,respectively,and the isothermal heat Q is as high as 0.921 k J·kg-1.Compared with the ceramic samples of the same composition without glass added,the temperature change and isothermal heating of the electrocaloric are increased by 69%and 36%,respectively,and the electrocaloric entropy change is kept above80%of the maximum value in the wide temperature range from 30?to 160?,indicating good temperature stability.It can be seen that the addition of glass has further improved the refrigeration capacity of PLZST ceramics. |
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