Studies On The Electrocaloric And Energy Storage Effect Of Lead-based Ferroelectric Thin Films

The electrocaloric(EC)effect of ferroelectric/antiferroelectric thin films have broad prospects in temperature control fields such as chip refrigeration.It is significance for solving the heat dissipation problem of microelectronic devices in integrated circuits.Moreover,due to its high-power density,fast discharge rate,stable energy storage characteristics,long cycle life and environmental protection,it can also be widely used in advanced electromagnetic pulse weapons,high-power radars,key medical devices,new energy vehicles and other fields.In this paper,the sol-gel method was used to successfully prepare BiFeO₃ and La co-doped PbZr_0.70Ti_0.30O₃ epitaxial ferroelectric thin films on(100),(110)and(111)oriented Nb-doped SrTiO₃(STO)single crystal substrates.The influence of orientations single crystal substrates on the electrocaloric effect and energy storage effect of the epitaxial thin films was systematically studied.The Nb-doped Pb(Zr_0.65Sn_0.3Ti_0.05)O₃ antiferroelectric thin film was successfully prepared on the LaNiO₃ and Pt(111)/TiOx/SiO₂/Si(100)composite substrate by the sol-gel method.The system analyzes the effect of frequency on the electrocaloric effect and energy storage effect of the antiferroelectric thin film.The results show:(1)Using sol-gel technology,a high-quality BiFeO₃ and La co-doped PZT epitaxial ferroelectric thin film was successfully prepared on a Nb-doped SrTiO₃(STO)single crystal substrate.Through the orientation control of the substrate,combined with the coupling of electric field,stress field,temperature field,etc.have obtained two electrocaloric(EC)effect temperature change peaks of the epitaxial thin films deposited on the(100),(110)and(111)oriented substrates,one is located near room temperature,and the other is located near around the peak of the dielectric permittivity.The thin film deposited on the(111)oriented STO substrate exhibited a stronger EC effect(?20.6 K at 1956 kV/cm)than deposited on the(100)and(110)oriented near room temperature.However,the thin films deposited on the(100)and(110)oriented STO substrates exhibited a stronger EC effect(?18.8 K at 1852 kV/cm and?20.8 K at 1230 kV/cm,respectively)around the peak of the dielectric permittivity(Tm?375 K).Particularly,as the direction of the applied electric field was switched(E<0),the ?T of the(100)oriented thin films around Tm was enhanced significantly from 18.8 K to 38.1 K.This experimental phenomenon can be attributed to the self-induced-poling caused by the out-of-plane tensile strain caused by the lattice mismatch between the substrate and the films during preparation process.Besides,the three oriented thin films have obtained higher energy storage density,better energy storage efficiency and higher temperature stability.Under an electric field of about 2200 kV/cm,their energy storage densities are 34.6 J/cm(100),33.0 J/cm(110)and 28.6 J/cm(111),and their energy storage efficiencies are 85%(100),76%(110)and 66%(111),respectively.For electrocaloric and energy storage effects of ferroelectric thin films,in addition to the important influence of orientation,application frequency on thin films performance cannot be ignored.Therefore:(2)The macroscopic phenomenological statistical model is used to obtain the contribution of the dipole to the dielectric response of the thin film at different frequencies,and then it is found that the frequency change has a greater impact on the electrocaloric and energy storage effects of the film.At around room temperature(?293 K)and at 10 kHz,the PZST antiferroelectric film has a large positive EC effect,and its ?T and ?S are 13.3 K and-13.6 J/K·kg,respectively;near the peak of the dielectric permittivity(?425 K)and at 100 Hz,a large negative EC effects is obtained,and its ?T and ?S are-5.8 K and ?S?4.5 J/K.kg.Moreover,the absolute value of the temperature change of the large positive and negative EC effects are sensitive and dependent to the applied frequencies.As the applied frequency increases,the positive EC effect intends to increase,while the negative EC effect intends to decrease as the applied frequency increases.This phenomenon is ascribed to the co-coupling between the phase-transition(nanoscale tetragonal transferring into rhombohedral along the direction which is vertical to the surface of the thin film,namely the[111])&defect dipoles.At 10 kHz,the coefficient of performance COP)and electrocaloric coefficient(?T/?E)are?3.37 and?0.01 K·cm/kV,respectively.Besides,under an electric field of about 2200 kV/cm,their energy storage densities are 15.7 J/cm(100 Hz),16.3 J/cm(1 kHz)and 17.0 J/cm(10 kHz),and their energy storage efficiencies are 42%(100 Hz),48%(1 kHz)and 50%(10 kHz),respectively.