Growth,structure And Electrical Properties Of CuO And MnO₂ Doped K_0.5Na_0.5NbO₃-BabiO₃ Single Crystal

Piezoelectric material is a kind of functional material which plays an important role in the field of electronic information.At present,piezoelectric materials containing lead are mainly used in the market.However,due to the strong corrosivity of lead in piezoelectric materials,heavy metal pollution in the process of preparation,application and waste disposal will cause immense harm to the environment and human health.For the sustainable development of human society,environmental friendly lead-free piezoelectric materials have become the focus of widespread attention.In this paper,lead-free piezoelectric single crystal is studied systematically from crystal growth to crystal structure anditsrelationshipwithproperties.Inthispaper,（1-x）(99.7K_0.5Na_0.5NbO₃-0.3BaBiO₃)-x MnO₂and（1-x）(99.7K_0.5Na_0.5NbO₃-0.3BaBiO₃)-x CuO piezoelectric single crystals were prepared by solid phase growth technique.The growth process,composition,microstructure and electrical properties of the crystals were systematically studied.The main research contents and results are as follows:Firstly,the effect of small amount of MnO₂doping on the structure and properties of99.7K_0.5Na_0.5NbO₃-0.3BaBiO₃based piezoelectric single crystal was studied.The result shows that the addition of trace manganese is helpful to the crystal growth.With the increase of the doping amount of MnO₂,the crystal surface becomes more flat and smooth,and the crystal quality and electrical properties are improved.When the doping amount is0.1 at%,the maximum piezoelectric coefficient d₃₃=351 p C/N is about three times that of the undoped crystal,the dielectric loss tanδ=0.02,the residual polarization intensity P_r=24.24μC/cm²,the coercive field E_C=5.31 k V/cm,the transition temperature of orthogonal phase and tetragonal phase T_O-T=167℃and the Curie temperature T_C=418℃.The doping of two kinds of metal oxides can reduce the defects of crystal samples and make the crystal surface smooth.In terms of structure,the orthogonality structure of crystal samples is not changed by MnO₂doping,but a small amount of tetragonal phase appears in the crystal samples due to the CuO doping.In terms of performance,both kinds of doping can effectively reduce the dielectric loss of crystal,the difference is that MnO₂doping is more obvious in optimizing the piezoelectric coefficient of crystal,while CuO is better in optimizing the ferroelectric properties of crystal,and can effectively increase the mechanical quality factor of crystal.Secondly,the effect of CuO doping on the structure and piezoelectric properties of99.7K_0.5Na_0.5NbO₃-0.3BaBiO₃single crystal was studied.The results show that CuO doping,like MnO₂,has good fluxing effect and can promote grain growth.A small amount of tetragonal phase appears in the crystals with the original phase structure of orthogonalized phase.When the doping amount is 0.1 at%,the tetragonal phase in the crystals reaches 16.14%.With the increase of CuO doping amount,the ferroelectric properties of the crystal generally increase,while the piezoelectric properties increase first and then decrease.When the doping amount is 1 at%,the crystal has the best comprehensive properties:P_r=44.07μC/cm²,the coercive electric field E_C=5.47 k V/cm,the piezoelectric coefficient d₃₃=117 p C/N,T_O-T=153℃,T_C=403℃.Finally,the effects of different cooling rates on the structure and properties of 0.5 at%MnO₂doped 99.7K_0.5Na_0.5NbO₃-0.3BaBiO₃crystals during the crystal growth stage were studied.The results show that the change of cooling rate has little effect on the crystal structure.The lower the cooling rate,the flatter the crystal growth surface,the size of the single crystal is larger,and the piezoelectric properties of the crystal are higher.When the cooling rate is 0.5℃/min,the crystal has the highest comprehensive performance,the positive piezoelectric coefficient d₃₃is 214 p C/N,the inverse piezoelectric coefficient d^*₃₃is 517 pm/V,and the crystal also has low dielectric loss tanδ=0.02,T_O-T=155℃,T_C=407℃.