Research On The Seed-free Solid-state Growth,Structure And Electrical Properties Of Tantalum With Manganese And Cobalt Doped Potassium Sodium Niobate Based Piezoelectric Single Crystals

With the improvement of health concepts and environmental awareness,piezoelectric materials widely used in electronic equipment are walking on the road of lead-free,and the use of non-lead elements to develop products with properties close to lead-based materials has greater social significance.In the lead-free piezoelectric system,potassium sodium niobate(K_xNa_1-xNb O₃,KNN)based piezoelectric material has excellent ferroelectric and piezoelectric properties and ideal high temperature working conditions,so it has been widely studied.In this paper,99.7K_0.5Na_0.5Nb O₃-0.3Ba Bi O₃ based piezoelectric single crystals doped with tantalum and co-doped with manganese or cobalt were prepared by seed-free solid-state crystal growth（SFSSCG）method respectively.And in order to obtain piezoelectric single crystals with excellent size and performance,their growth,phase structure,microstructure and electrical properties were systematically studied.The main research contents and results are as follows:The effects of tantalum doping on the growth of 99.7K_0.5Na_0.5Nb_1-xTa_x-0.3Ba Bi O₃-based piezoelectric single crystal by seed-free solid state crystal growth were studied.The results show that the doping of tantalum is conducive to the growth of crystals,and with the increase of tantalum doping,the size of single crystals increases.All tantalum-doped KNNTx-BB single crystals show a natural surface of layered growth,with a relatively flat and dense surface of the corroded single crystal,and all crystals have 180°electrical domains.With the increase of tantalum doping,the residual polarization P_r and the piezoelectric constant d₃₃ of single crystals first decreased and then increased and finally decreased,and the P_r and d₃₃ reached the maximum of 17.79μC/cm² and 251 p C/N respectively when the tantalum doping amount x is 0.008.In addition,the doping of tantalum did not alter the orthogonal phase structure of KNNTx-BB single crystals clearly,and the doping of 1.0 mol%and 1.2 mol%of tantalum significantly increased the transition temperature from the orthogonal phase to the tetragonal phase(T_O-T)of KNNTx-BB single crystals,which were about 212.3°C and 212.4°C respectively.The effects of tantalum and manganese mono-doping respectively and tantalum-manganese co-doping on the growth,structure and properties of 99.7K_0.5Na_0.5Nb O₃-0.3Ba Bi O₃-based piezoelectric single crystals were studied.The results show that tantalum-manganese co-doping is more conducive to the seed-free solid state growth of KNNTx-BB crystals than mono-doping respectively,and the maximum size of single crystal can reach 30.0×9.2×2.6 mm³ when 0.1 mol%manganese and 0.9 mol%tantalum co-doped.With increase of the doping amounts of tantalum in the tantalum-manganese co-doping KNNTx-BB crystals,the phase structure first transformed from orthogonal phase and tetragonal phase coexistence structure to orthogonal phase structure,and then to orthogonal phase and tetragonal phase coexistence structure again.When the doping amounts of 0.1 mol%manganese were fixed and the doping amounts of tantalum increasing,the ferroelectric and piezoelectric properties of KNNTx-BB single crystal is increased,and when the doping amounts of tantalum and manganese were 0.9 mol%and0.1 mol%respectively,the single crystal obtains larger residual polarization P_r and piezoelectric constant d₃₃,which are 26.96μC/cm² and 247 p C/N respectively.The effects of tantalum-cobalt co-doping on the seed-free solid state growth,structure and electrical properties of 99.7K_0.5Na_0.5Nb O₃-0.3Ba Bi O₃-based piezoelectric single crystals were studied.The results show that when the doping amounts of 0.1 mol%cobalt were fixed and the doping amounts of tantalum were increasing,the degree of clustering of small grains decreases,and the size of single crystals increases.The single crystal size of0.1 mol%cobalt and 1.1 mol%tantalum co-doped KNNTx-BB can reach 19.0×11.0×1.3mm³.With the increase of tantalum doping amounts in tantalum-cobalt co-doping KNNTx-BB crystals,the phase structure transformed from orthogonal phase and tetragonal phase coexistence structure to orthogonal phase structure.When the 0.1%cobalt doping amounts were fixed and the amounts of tantalum doping were increased,the residual polarization P_r,piezoelectric constant d₃₃,and thickness direction electromechanical coupling coefficient k_tof KNNTx-BB single crystal are increased first and then decreased,and the maximum d₃₃was obtained when the tantalum doping amounts is 0.3 mol%,which is about 776 p C/N.