Investigation On Doping And Properties Of Bismuth Ferrite Based Lead-free Piezoelectric Ceramics

Bismuth ferrite-based lead-free piezoelectric ceramic materials,?1-x?Bi Fe O₃-x Ba Ti O₃?BFO-BTO?with a perovskite structure,are promising candidates for widely industrial application due to their good piezoelectric properties and high Curie temperatures.However,the volatility of Bi and the conversion of Fe²⁺and Fe³⁺during sintering,result in relatively large leakage current and deteriorating properties.Therefore,it's necessary to carry out the modification of the materials.In this paper,the additives such as oxide and perovskite compound ABO₃ were employed to investigate the effect of Mn O₂,Cu O and Bi(Mg_2/3Nb_1/3)O₃?BMN?on sintering behavior,phase composition,microstructure and electrical properties of BFO-BTO materials.The main contents are as follows:Firstly,the effect of Mn O₂ on the structure and electrical properties of 0.7BFO-0.3BTO ceramics is investigated.Doping Mn O₂ would improve the densification and uniformity of the ceramics and the resistivity as well,but inhibit grain growth.Doping Mn O₂dopant also results in lattice distortion,and the tetragonal structure occurs at an addition of 0.5wt%Mn O₂.With the increase of Mn O₂,the Curie temperature decreases a little,meanwhile the Curie peak becomes flat and broad gradually,which indicates the characteristics of relaxation.A proper amount of Mn O₂ can reduce dielectric loss of the ceramic samples.When the doping content of Mn O₂is 0.1?0.3wt%,the ceramics show a low value of dielectric loss.Secondly,the effect of Cu O on the structure and electrical properties of0.7BFO-0.3BTO+0.1wt%Mn O₂ ceramics is investigated.As an effective sintering aid,Cu O can obviously enhance the densification and grain growth,and dramaticaly improve the piezoelectric and ferroelectric properties of the 0.7BFO-0.3BTO+0.1wt%Mn O₂ceramics.Cu O promotes the transition from relaxor to normal ferroelectrics,and increases Curie temperature from 450??x=0?to 490??x=0.05?,with a remarkably high value of Curie peak and dielectric loss at high temperature.Doping Cu O would change the conductive mechanism of 0.7BFO-0.3BTO ceramics.When the doping amount of Cu O is 0.2wt%,the piezoelectric constant shows a good temperature stability?T_d=?500??,and the ceramics exhibit the optimum electric properties:d₃₃=178p C/N,T_c=510?,k_p=0.2416,P_r=8.63?C/cm²,E_c=8.99k V/cm.Lastly,the effect of BMN on the structure and electrical properties of 0.7BFO-0.3BTO ceramic is investigated.The result indicates the formation of a good solid solution between BMN and BFO-BTO,and the substitution of(Mg_2/3Nb_1/3)³⁺complex ions for B site leads to compositional nonuniformity of microdomain,which causes relaxation.BFO-BTO materials become ideal relaxor ferroelectrics by adding 0.02mol of BMN.The value of Curie peak?_mand Curie temperature T_m of 0.7BFO-0.3BTO ceramics decrease gradually with increasing dopant of BMN.Piezoelectric and ferroelectric properties are also improved at a suitable doping amount of BMN.