Study On Densification And Properties Of PbNb₂O₆ High Temperature Piezoelectric Ceramics

Piezoelectric ceramics can convert mechanical energy into electrical energy and become an important functional material.Piezoelectric ceramics with a Curie temperature higher than that of PZT have attrac.ted wide attention due to their ability to act as sensors and actuators in higher temperature environments.The Curie temperature of lead metaniobate is about 570^oC,much higher than that of conventional PZT,and is considered to be the most promising high-temperature piezoelectric material.PbNb₂O₆ is the earliest discovered ferroelectric body with tungsten bronze structure.It has much outstanding features:1.lead metaniobate is often used as an ultrasonic sensor because of its low mechanical quality factor;2.the large anisotropy?the radial electromechanical coupling coefficient is almost negligible with respect to the longitudinal electromechanical coupling coefficient?makes it possible to produce a better response under hydrostatic pressure,thus making it better in ultrasonic sensing application;3.high Curie temperature makes lead metaniobate more useful in high temperature applications.In addition to the above advantages,lead hemitanide has some disadvantages.Under normal circumstances,the ferroelectric phase of lead metaniobate is metastable,and this ferroelectric phase is difficult to obtain.The usual solid phase sintering method leads to lead metasulphate that is basically a mixed phase.The preparation of lead metaniase is very difficult,because there isthe transition from rhombohedral to tetragonal phase during the sintering process.This phase transition will lead to the abnormal growth of crystal grains of lead metagermanate in the process of ceramic formation,and it is accompanied by the generation of cracks and voids.Due to the previous defects and other reasons,the piezoelectric performance of lead metaniobate is insufficient,and its piezoelectric coefficient is not high enough.This study intends to address the difficulties of PbNb₂O₆,such as difficult sintering,low density,and insufficient piezoelectric performance.Two experimental schemes are proposed.First,by adjusting the contents of different Nb₂O₅ in PbNb₂O₆high temperature piezoelectric ceramic raw materials,the problems of difficult sintering,low density,low electromechanical coupling coefficient and insufficient piezoelectric coefficient of pure PbNb₂O₆ are solved.The other is through the morphotropicphaseboundarymaterialofCa²⁺modulatingcomponent Pb_0.56Ba_0.44Nb₂O₆ to raise the Curie temperature as low as possible at d₃₃.The main conclusions obtained in the experiment of this study are as follows.By adding excess Nb₂O₅ into lead metaniobate,high temperature piezoelectric ceramic with a density of up to 93.2%,a Curie temperature of 552°C and a piezoelectric coefficient of 69 pC/N was prepared.By thermal XRD analysis,Nb₂O₅added to the PN played a role in suppressing the ternary to tetragonal phase transition of the PN in the sintering process,thereby suppressing the abnormal grain growth and increasing the density.Through Raman analysis,Nb⁵⁺occupies the C position,causing disorder of the cations in the PN and distortion of the oxygen octahedron.As a result,the Curie temperature tends to rise and causes the piezoelectric coefficient to rise.By further refining the above experiment,the components were optimized near the group of PN-5 mol%Nb₂O₅.Through testing the performance of refined component samples,comparative analysis found that excess Nb₂O₅ was added to the PN,causing changes in the PN performance to show stages.Previous experiments have found that Nb⁵⁺is entering the lattice.In connection with this experiment,this shows that Nb₂O₅ added to the PN is two places:1.Entered the lattice;It is enriched at grain boundaries?through the research of other scientific researchers?.And the composition of the PN-6 mol%Nb₂O₅ piezoelectric properties is the best,the Curie temperature of 553 ^oC.By introducing Ca²⁺into Pb_0.56Ba_0.44Nb₂O₆ at the morphotropic phase boundary of PN,a PN-based ceramic with a higher Curie temperature and good piezoelectric performance was prepared.Through SEM test analysis,it was found that the introduction of Ca²⁺refines the ceramic grains.Analysis of the dielectric thermograms revealed that the introduction of Ca²⁺made the dielectric constant of the material very flat before 200 ^oC.And this also makes it possible to use this material in energy storage applications.