Research On The Electrostrain Performance Of Bi_0.5Na_0.5TiO₃-Based Leadfree Ferroelectric Ceramics

Lead-based piezoelectric ceramics such as lead zirconate titanate（PZT）are widely used in medical,electronic,automotive,communication,mechanical,aerospace,military,and other fields due to their excellent piezoelectric and driving characteristics and currently occupy a leading market position.However,lead-based piezoelectric ceramics can cause environmental pollution and health hazards during the production and use process,so the development of environmentally friendly piezoelectric ceramics that can replace lead-based has become the focus and hot spot of current research.Sodium bismuth titanate(Bi_0.5Na_0.5Ti O₃,BNT)is a potential substitute for lead-based materials due to its outstanding advantages such as excellent piezoelectric properties,high curie temperature,stable chemical properties,and strong ferroelectricity.In this paper,BNT-based piezoelectric ceramics were selected as the research object,and strain characteristics were studied.By dissolving barium titanate（Ba Ti O3,BT）into BNT ceramics for performance optimization,when the molar content of BT is6%,the ceramic phase structure changes from a triangular phase to a coexistence of a triangular phase and a tetragonal phase.In addition,the introduction of BT can effectively reduce the ferroelectric-relaxation phase transition temperature,and BNBT ceramics achieve a large strain of 0.396%at 110℃.Based on the above research,the A/B site co-doping strategy is used to improve the strain properties of BNT-based ceramics to obtain new lead-free piezoelectric ceramics with excellent strain properties.The research shows that the introduction of Na Ta O₃（NT）will induce the transformation of the phase structure of BNBT from the coexistence of tripartite and tetragonal phases to the pseudo-cubic phase,which can effectively control the ferroelectric-relaxation phase transition temperature,destroy macro-domains,promote the formation of polar nano-domains regions,enhance the degree of local structure disorder,and reduce polarization response.BNBT-3NT obtained a positive strain of 0.394%at 65 k V/cm with an inverse piezoelectric coefficient of 606 pm/V.The introduction of Li Ta O₃（LT）into the BNBT will induce the generation of ergodic relaxation phases and destroy the ferroelectricity,reducing residual polarization,maximum polarization,and coercive field.BNBT-3LT obtains a positive strain of 0.439%at 80 k V/cm with an inverse piezoelectric coefficient of 548pm/V.The introduction of Sr Sn O3（SS）into the BNBT ceramic reduces the ferroelectric-relaxation phase transition temperature and enhances the diffusion properties of the ferroelectric to ergodic relaxation phase transition,reduces the maximum dielectric constant,and broadens the dielectric temperature peak.The positive strain of the BNBT-2SS ceramic is 0.445%at 80 k V/cm with an inverse piezoelectric coefficient of 556 pm/V.Although a solid solution of Ca Sn O₃（CS）in the matrix does not affect the single perovskite structure of BNBT ceramics,it can reduce the anisotropy of crystal cells.The introduction of CS can regulate the ferroelectric-relaxation phase transition temperature to near room temperature,enhance the relaxation characteristics of ceramics and reduce the ferroelectricity of materials.BNBT-3CS ceramics obtain a positive strain of 0.368%at 80 k V/cm with an inverse piezoelectric coefficient of 458 pm/V.After introducing Bi Al O₃（BA）into the BNBT matrix,Bi³⁺and Al³⁺occupy the A and B positions of the perovskite structure,respectively,enhancing the ionic disorder at the A and B sites,disrupting long-range ferroelectric ordering,enhancing the relaxation characteristics of the material,inducing the transition of ferroelectrics into relaxor ferroelectrics,and reducing residual polarization,coercive field,and maximum polarization.Finally,BNBT-2BA ceramics can obtain a large positive strain of 0.432%at 60 k V/cm with an inverse piezoelectric coefficient of 724 pm/V.In conclusion,BNBT ceramics were modified by A/B site co-doping modification strategies to optimize the performance,the correlation between structure and performance was explored,and a series of lead-free ferroelectric ceramics with good electrostrain performance were developed,which could provide a theoretical basis and potential candidates for the development of new lead-free ceramic drivers.