Study On Electrocaloric Effect Of Oxide Doped Ba_0.65Sr_0.35TiO₃ Ceramics

Conventional refrigeration technology uses a large amount of refrigerant such as freon to seriously damage the ozone layer.It is considered to be an effective way to replace the traditional vapor compression cycle refrigeration technology with solid state card effect refrigeration technology.The use of the principle of the card effect to prepare a new type of solid-state refrigeration device that is environmentally friendly,energy-saving,efficient and easy to miniaturize has broad application prospects.Ba1-xSrxTiO3(BST)ceramics have the advantages of adjustable curie temperature,excellent dielectric properties,excellent electrocaloric effect,energy saving and environmental protection.In this paper,BST was selected as the main research object,the effects of sintering parameters on the sintering characteristics,dielectric properties,electrocaloric effect and pyroelectric effect of BST were studied in detail.The methods of doping SiO2 and CeO2 were adopted.The sintering characteristics,the performance of the electrocaloric effect and the dielectric properties are improved by doping SiO2 and CeO2,and the relationship between the properties is explained in detail.The main results of this study are as follows:1.Ba0.65Sr0.35TiO3 ceramics were prepared at 1360? and 1380? for 3,4,5h.The results showed that the prolongation of the soaking time will gradually promote the appearance of the visible pores on the surface of the sample,while reducing the dielectric constant frequency stability of the sample,but it will help to improve the temperature stability of the dielectric properties of the material.The sample sintered at 1380? for 3h possess the best electrocaloric performance,?Tmax=0.65K at room temperature(20?),and ?Tmax/?E was as high as 1.86×10-7 K.m/V.In addition,for the pyroelectric effect of BST ceramics,the sample sintered at 1380? for 4h has the largest open circuit voltage(?)and short circuit current(?),were 0.42V,120nA,while the effect of shading and exposure speed on V and I was unconspicuous.The sample sintered at 1380? for 5h had an average power of P=0.55nW under the condition of a load of 50M? and exposure speed of 20r/min.2.BST+x%SiO2(x=1,2,3,5)ceramics were prepared at 1360?C and 1380?,respectively.The results showed that the doping of SiO2 does not change the crystal structure of B ST ceramics,and it was beneficial to the process of grain surface densification,improving the grain size uniformity and the frequency stability of the dielectric properties of the sample.With the doping amount of SiO2 Increasing,the dielectric constant of BST ceramics was reduced monotonously,and the dielectric dispersion characteristics were also enhanced accordingly.In addition,the electrocaloric effect of the sample sintered at 1360? was better than that of the sample at 1380?.The ?Tmax and ?Tmax/?E of BST+3%SiO2 ceramics kept at 1360 ?for 3h were 1.6K,8.00×10-7K·m/V,respectively.The open circuit voltage peak(Vmax)and the short circuit current peak(Imax)are 170nA and 1.5V,respectively,and the average power Pmax=0.4nW at a load of 50M? and a speed of 80r/min.3.BST+ x%CeO2(x=0.5,1,2,4)ceramics were prepared at 1360? and 1380?,respectively.The results showed that the doping CeO2 does not change the crystal structure of BST ceramics,but also reduced the grain size and improved the dielectric stability.The dielectric constant of ceramics increased first and then decreased with the increase of CeO2 doping amount.The electrocaloric effect of the sample sintered at 1380 ? was better than that of the sample at 1360 ?.The ceramics which were kept at 1380? for 3h had the best electrocaloric effect.The ?Tmax and?Tmax/?E are 1.2K and 8.57×10-7K·m/V,respectively,and the ceramic's ?Tmax/?E was 3.5 times larger than pure BST ceramics.The pyroelectric effect of BST+0.5%CeO2 and BST+2%CeO2 ceramics were the best,and the short-circuit current peak(Imax),open circuit voltage peak(Vmax)and corresponding speed(r)are 154nA/0.9V(10r/min)and 115nA/0.63V(80r/min),respectively,the average power is increased by nearly 10 times compared to pure BST ceramics and SiO2-BST ceramics.