Phase Transformation Behavior And Negative Electrocaloric Effect Of Yb Doped PbZrO₃ Antiferroelectric Thin Films

Internet of things?Iot?era is the era of the sensor,and the MEMS microelectro-mechanical system is at the core of the sensor.Because of the presence of the unique phase transformation behavior from antiferroelectric to ferroelectric induced by the electric field,antiferroelectric materials have shown potential application in the field of MEMS refrigeration technology.Recently,PbZrO₃?PZO?with a ABO₃ perovskite structure is one of the most widely studied typical antifereoelectric materials.This research fabricated a kind of Yb-PZO?PYZ?antiferroelectric thin film,with Yb doped concentration of 0 mol%,0.5 mol%,1.0 mol%,3.0 mol% and 5.0 mol%,which were deposited on the substrates of Pt?111?/Ti/SiO2/Si,by a sol-gel method,the pre-heating process at 450 ?,and the rapid thermal annealing process at 650 ?.On the basis of the preperation,the X-ray diffractometer?XRD?and the Scanning electron microcopy?SEM?were used to characterize the microstructure and the morphology,respectively.The fereoelectric and dielectric performance were investigated and tested using the ferroelectric tester and impedance analyzer.Finally,the phase transition behavior and the negative ECE?electrocaloric effect?induced by the temperature and the electric field were evaluated and calculatedThrough the preparation process which the thin films were pre-heated at 450 ? for3 minutes and annealed at 650 ? for 3 minutes,XRD results revealed that all the fabricated thin films exhibited pure perovskite without other impurity phases.Moreover,with the increase of Yb doped content from 0 mol% to 5.0 mol%,the intensities of diffraction peaks of?100?,?110?and?200?were changed dramatically.The intensity of?100?and?200?decreased while that of?110?increased,and the orientation degree of?100?peak minished to 4.13 % from 70.31 % while that of?110?peak enlarged to92.15% from 23.42%.Therefore,the high Yb doped concentration was indentified as an effective method to obtain the?110?highly-orientated PYZ thin films.SEM results showed that the surfaces of all the thin films were fine and close,with apparent interface,and had good surface wettability with the substrates.On the basis of testing the ferroelectric and dielectric properties,the phasetransformation behaviors of PYZ thin films with different Yb modified contents.Firstly,all the thin films had a double hysteresis loop at the normal temperature and had a low remant polarization when the electric field was withdrawn,which meant that all the films were antiferroelectrics.What's more,at the low applied electric field,the polarization of thin films alomost had a linear relationship with the applied electric field,which showed that the applied was not encough to induce the reversal of the antiparallel dipoles,and the thin films were still antiferroelectrics at the applied electric field.When the electric field was augmented continuously,the polarization of thin films began to increase suddenly,and exhibited a nonlinear relationship with the electric field,which suggested the PYZ thin films began the phase transition process.Furthermore,when the temperature and the electric field were combined to influence the phase transition behaviors,a lower electric field was applied to induce the antiferroelectric phase into the ferroelectric phase or the paraelectric phase when the temperature was increased.That's to say,the temperature and the electric field had a synergistic effect in inducing the phase transformation.Lastly,with the addition of the Yb content from 0 mol% to 5mol%,the electric field at which the the antiferroelectric phase was changed into the ferroelectric phase was improved initially and then weakened,so at the Yb content lower than 1.0 mol%,the antiferroelectric phase was stabilized but the ferroelectric phase was stabilized at the content higher than 1 mol%.In order to analyze and evaluate the negative ECE?electrocaloric effect?of Yb doped PZO thin films,this research adopted the indirect method to describe and calculate the ECE in the form of the electrocaloric temperature change??T?and the electrocaloric entropy change??S?,based on the Maxwell thermodynamics equation.The results suggested that,with the increase of Yb doped content from 0 mol% to 5.0mol%,the minimum ?T decreased firstly to-12.88 K at 50 ? from-6.88 K at120 ?,which was close to the room temperature but then decreased to-1.25 K.Therefore,at the Yb content lower than 1.0 mol%,the antiferroelectric phase was stabilized but the ferroelectric phase was stabilized at the content higher than 1.0 mol%.Taking all the results and analysis above into consideration,the negative electrocaloric effect could be adjusted and optimized by a rational modification with a optimal Yb doping content,and a kind of novel antiferroelectric thin film with atremendous electrocaloric temperature change at the temperature close to the room temperature was prepared,which provided the fundamental research achievement for the MEMS refrigeration.