Effect Of A/B Site Co-doping On Energy Storage Properties And Phase Structure Of BNT-based Ceramics

As renewable energy develops rapidly,high energy density and fast charge/discharge rates have been the key development direction for dielectric capacitors.Among the energy storage materials,although lead-based materials generally have excellent energy storage properties,it is urgent to explore a green and environmentally friendly lead-free material to replace them as environmental problems become serious.Among them,Bismuth sodium titanate(Bi_0.5Na_0.5Ti O₃,BNT)-based ferroelectric ceramics are easy to obtain high energy storage density due to their strong ferroelectricity and abundant optimization approaches.However,how to further improve the energy storage density and efficiency（η）of BNT-based ceramics is a hotspot and difficulty in current research.In the selection of BNT-based ceramics,to mitigate the decrease in ferroelectricity during the doping process,a strong ferroelectricity Bi_0.48Na_0.48Ba_0.04Ti O₃（BNBT）ceramic containing barium ions was selected as the research matrix,and the A/B site element co-doping method was adopted.A systematic study was carried out on the structures and electrical properties of ceramics and provided new ideas for the development of high-properties lead-free energy storage ceramics.（1）Effects of different contents of Nd_1/3Nb O₃（NN）on BNBT ceramics.The NN was doped into BNBT ceramics to improve the relaxor properties of the ceramics by increasing the atomic disorder and turning FE domains into RFE nanodomains,and to improve the breakdown resistance of the ceramics by refining the grains,reducing the dielectric loss,and widening the band gap.A recoverable energy storage density(W_rec)of 5.3 J/cm³ andηof 61.0%were obtained in the 0.94BNBT-0.06NN ceramics,with good stabilities and charge/discharge properties.（2）Effects of different contents of La_1/3Nb O₃（LN）on BNBT ceramics.Based on the research results that NN doping can improve the energy storage properties of BNBT ceramics,A-site Nd³⁺ions were replaced for large-sized La³⁺ions.The higher content of LN doped into BNBT ceramics improved the relaxor properties of ceramics,and delayed the polarization saturation.Meanwhile,the breakdown resistance of ceramics was enhanced by grain refinement,dielectric loss reduction,and maintenance of a wide band gap.A high W_rec of 6.5 J/cm³ andηof 73.3%were obtained in the 0.91BNBT-0.09LN ceramics,with well frequency stability,temperature stability,and charge/discharge properties.（3）Effect of different contents of Sm_1/3Nb O₃（SN）on BNBT ceramics.Based on the results and rules of the previous two research,La³⁺ions in the A-site were replaced with Sm³⁺ions,and the preparation process was optimized.The higher contents of SN were doped into the BNBT ceramics,which improved the relaxor properties and breakdown resistance of the ceramics and further delayed the polarization saturation.An ultra-high W_rec of7.4 J/cm³ and a highηof 77.8%were obtained in the 0.88BNBT-0.12SN ceramics,with excellent frequency stability,temperature stability,and charge/discharge properties.The above research results obtained by the control variate method show that suitable selected and modified A/B site elements of co-doping can improve the energy storage properties of BNBT ceramics by improving the relaxor properties and breakdown resistance.