The Energy Storage Properties And The Electrocaloric Effect Properties Of Non-stoichiometric Lead Lanthanum Zirconate Titanate Based Ceramics

In this paper,several series of B-site non-stoichiometric PLZT ceramic materials were prepared by the traditional solid phase reaction synthesis process.Firstly,the antiferroelectric PLZT2/95/5 was synthesized.The effects of different B-bit ratio changes on the microstructure and electrical properties of the PLZT system were studied.Then,based on this work,the antiferroelectric PLZT2/95/5was used as the matrix to study the effect of barium ferrite（BF）doping on the system performance.The last,the effects of different B-bit ratios on the microstructure and electrical properties of lead-acid（PLZT9/65/35）relaxed ferroelectric ceramics were investigated.The following three aspects were mainly introduced:First,(Pb_0.97La_0.02)(Zr_0.95Ti_0.05)_1+yO₃（y=-0.03,-0.01,0.01 and 0.03）antiferroelectric ceramics were prepared by a high temperature solid phase method.XRD results induced that all samples showed a good perovskite structure.The phase transition peak appears in the dielectric temperature spectrum,and the Curie temperature and dielectric constant of the sample change with the y value.According to Arrhenius’s law,the mechanism of high temperature dielectric relaxation is analyzed from the aspect of activation energy.The impedance activation energy is about 0.89 eV-1.38 eV,the relaxation mechanism of the material is controlled by dipole conduction,and the dynamic thermal motion of the ionized oxygen vacancies can explain this behavior.The ferroelectricity and energy storage characteristics of the samples were studied.The ferroelectric and antiferroelectric phase transitions were observed in each sample.When y=-0.03,the maximum effective energy storage density(W_re)reached 0.98 J/cm³.The corresponding energy storage efficiency（?）is82%.In addition,ceramic samples also exhibit a giant negative Electrocaloric Effect.According to Maxwell’s relationship,when y=-0.01,E=50kV/cm,the maximum adiabatic temperature change（ΔT）reaches-12.45K.The ferroelectric-antiferroelectric phase transition near Curie temperature was used to explaine the phenomenon.Second,a series of ceramics(Pb_0.97La_0.02)(Zr_0.95Ti_0.05)_0.97O₃-xBiFeO₃（x=0,0.02,0.04,0.06,0.08 and 0.10）were prepared in two steps through high temperature solid phase method.The samples are all perovskite structure.The addition of BF can eliminate the generation of heterophase in PLZT ceramics and stabilize the phase structure.The dielectric temperature spectrum shows an abnormal peak,and the abnormal performance is consistent when x=0⁰.06.With the increase of BF content,the dielectric constant of the sample increases first and then decreases,which is related to the leakage defect of BF itself;the macroscopic resistance of the sample has the characteristic of negative temperature coefficient,and the main carrier of high temperature dielectric relaxation is oxygen.Vacancies;the sample exhibited good ferroelectric properties,and the phase transition of ferroelectric and antiferroelectric was observed over a range of temperatures.The energy storage characteristics of the sample were studied.When x=0.06,the maximum effective energy storage density of ceramics was W_rec=0.69 J/cm³,?=73.4%.The sample also showed a more superior negative giant card effect,when x=0.06,E=40 kV/cm,ΔT_max=-17.88 K.Third,in this chapter,a series of B-site non-stoichiometric(Pb_0.91La_0.09)(Zr_0.65Ti_0.35)_1+yO₃ ceramics were prepared by high temperature solid phase method.The sample crystallized well.As the value of y increases in the negative direction,the dielectric constant of the sample monotonously increases,and the corresponding temperature moves toward the low temperature direction.The sample exhibits a giant dielectric constant phenomenon.When y=-0.05,the maximum dielectric constant is 79880.It is considered that electrical inhomogeneity leads to the generation of giant dielectric constant phenomenon.The sample has a relaxation characteristic,and the relaxation phenomenon caused by short-range jump of ions caused by oxygen vacancies.The increasing of y value weakens the ferroelectricity of ceramics to a certain extent.During the heating process,the sample gradually changes from ferroelectric phase to paraelectric phase,and exhibits a good relaxation in a wide temperature range.The best energy-storage results of the sample are:when y=-0.05,at room temperature,E=70kV/cm,W_re=0.36 J/cm³,?=58.1%.