Study On Electrostrain Of Sodium Bismuth Titanate Based Lead-free Ferroelectric Ceramics

Ferroelectric ceramic materials can undergo slight deformation under an electric field.This deformation has important applications in the fields of actuators,piezoelectric sensors,micro-displacers,and so on.At present,the ferroelectric ceramic materials used in the market are mainly lead-based materials.Because lead-based materials have a great harm to the environment and human health,lead-free piezoelectric ceramics with excellent strain properties have become researched focus.Sodium bismuth titanate(NBT)-based ceramics,due to the phase transition between the ferroelectric phase and the relaxation phase,can use this phase transition to obtain larger strain and become one of the most studied lead-free ferroelectric materials.As far as the current research is concerned,the strain properties of sodium bismuth titanate-based ceramics are still not comparable to those of lead-based materials,which greatly limits the practical application of sodium bismuth titanate-based ceramics.This subject takes NBT-ST ceramics as the research object.NBT-ST ceramics in different phase regions are respectively doped with MnO acceptor,Nb2O5 donor doping and MnO-Nb2O5 co-doped.The use of acceptors,donors and co-doping to regulate the hysteresis loops in different phase regions to obtain lead-free driving materials with excellent strain performance.In NBT-ST ceramics doped with MnO acceptors,Mn2+/Mn3+replaces Ti4+to form oxygen vacancies,and a defect dipole is successfully constructed in the ceramic lattice of the T-phase region.The reversible restoring force of domain reversal results in a PE hysteresis loop with a maximum polarization intensity Pm and a residual polarization intensity Pr tending to 0.When the doping amount of Mn is 1.Omol%,Under 60kV/cm of the electric field,the strain is the largest,about 0.22%,but the hysteresis is 14%;when the Mn doping amount is 0.5mol%,the hysteresis is the smallest,about 12%,but the strain is 0.2%.Secondly,in NBT-based ceramics doped with Nb2O5 donors,Nb5+replaces Ti4+,forcing Ti4+to become Ti3+,and Nb5+-Ti3+ion pairs are formed in NBT-ST ceramics in the T-phase region and quasi-homogeneous phase region.The formation of ion pairs significantly reduces the residual polarization Pr,resulting in a driving material with excellent strain properties.In the T phase,when the Nb doping amount is 0.5%,under an applied electric field of 60 kV/cm,although the strain is not large,the hysteresis is about 10%.In the quasi-homogeneous phase,when the Nb doping amount is 0.5%,the strain has a maximum value of about 0.37%under an applied electric field of 80 kV/cm,and when the Nb doping amount is 2.0%,the hysteresis has a minimum value,about 22.1%.Finally,in the MnO-Nb2O5 co-doped ceramics,it is found that the appropriate MnO doping content can increase the maximum polarization strength,to a certain extent,through the adjustment of the shape of the iron wire,and can significantly reduce the hysteresis without reducing the strain.When the Nb content is unchanged at 1.0%and the Mn doping amount is 0.25%,the strain is about 0.28%under 60kV/cm.Therefore,the experimental content of MnO-Nb2O5 co-doped NBT-based ceramics has brought new expectations for exploring larger strain and smaller hysteresis.