Properties Of Bismuth Sodium Titanate And Strontium Barium Niobite Based Lead-free Relaxor Ferroelectric Ceramics

Relaxor ferroelectric materials have important applications in electronic devices such as micro positioner,information storage,and smart capacitors.In recent years,with the enhancing awareness of environment protection and the increase in operating requirement for electronic equipment,lead-free relaxor ferroelectric materials have attracted more and more attention.Compared with lead-based relaxor ferroelectric ceramics,which have gained widespread industrial applications,the electrical properties of lead-free ceramics are usually lower than lead-containing ceramics,although they have the advantage of environment-friendly,thus making it difficult to commercialize the devices,Therefore,modification studies are needed to improve the performance characteristics.Of the many improvement methods,chemical doping is one of the most effective and feasible.In this paper,perovskite structure oxide sodium bismuth titanate and tungsten bronze structure oxide barium strontium barium niobate are selected as research objects,and chemical doping is used to form composite and solid solution ceramics respectively.The relaxor ferroelectric properties of ceramics are studied.The experimental results show that the two ceramics have excellent electrical properties and are expected to have potential applications in high-temperature and dielectric capacitors.This paper's work includes:?1?0.82[0.94Bi_0.5Na_0.5Ti O₃-0.06Ba Ti O₃]-0.18Ca Zr O₃:x Zn O?x=0,0.10,0.20,0.30,0.40?composite ceramics were prepared by solid-phase reaction method.XRD measurements show that the x=0 sample has a single-phase perovskite structure,the other samples are composite structures constructed by Zn O and BNT-BT-CZ.SEM results confirm that Zn O particles are distributed at the grain boundary of BNT-BT-CZ,and show a tendency of aggregation and growth;The composite ceramics show good dielectric properties with significantly improved temperature-insensitivity:the temperature range for low variance in permittivityfor the optimal x=0.10 at 1 k Hz.Especially,for the x=0.10 composite,the variance of permittivity is less than 4.0%in the temperature range of 30-400°C with the suitable permittivity value at 10 k Hz.By comparatively investigating the properties of unpoled and poled samples,the improved temperature-insensitive permittivity is rationalized by the Zn O-induced local electric field that can suppress the evolution of polar nanoregions and thus enhance the temperature-insensitivity of permittivity.?2?A lead-free relaxor ferroelectric solid solution?1-x?Sr_0.75Ba_0.25Nb₂O₆-x[0.94Bi_0.5Na_0.5Ti O₃-0.06Ba Ti O₃]?x=0,0.05,0.10,0.15,0.20?based on perovskite structure and tungsten bronze structure oxide ceramic system was prepared by solid state reaction method.The experimental results show that all the samples are single-phase with tungsten bronze structure and anisotropic columnar grains.The length-radius ratio of grain reaches a maximum of 10.5 at x=0.20;The ferroelectric curie temperature,dielectric constant and saturated ferroelectric polarization decrease from 36°C,507,3.2mC/cm² for SBN to-61°C,365,2.0mC/cm²for x=0.10,and then increase to 43°C,1167,5.5mC/cm² for x=0.20.Moreover,the solid solution shows excellent energy storage property due to its nearly ideal relaxor nature,the energy storage efficiency of x=0.10 sample can be as high as 93%.Such dependent composition of electrical properties are attributed to the competitive effects of B-site Ti⁴⁺and A-site Ba²⁺occupy in tungsten bronze lattice on ferroelectricity.This work provides an alternative thinking to design novel solid solution with high electrical performance.