The Effect Of Atmosphere And Calcination Temperature On The Structure And Electrical Properties Of Bi 0.5 Na 0.5 TiO 3 Based Lead-free Ceramics

In the preparation of sodium bismuth titanate(Na0.5Bi0.5TiO3,BNT)in the process of ceramic,due to the high temperature sintering,Bi3+ and Na+volatile,which may due to the introduction of the difference of oxygen vacancy concentration point defect,affect the structure of ceramic(including phase structure,microstructure and electrical performance.In this article,we use the method of solid phase for BNT ceramics material,burn and sintering phase in advance,in different atmosphere are pass(nitrogen,oxygen,etc.),to explore the structure of the atmosphere environment for sample(including the phase structure,microstructure and the effect of electrical performance.In addition,we study the differences in structure and electrical performance by changing the pre-temperature temperature of the ceramic.(1)(Na0.5Bi0.5)0.94Ba0.06TiO3 lead-free piezoelectric ceramics were prepared.The nitrogen and oxygen atmospheres were used separately during the calcination and sintering processes via a solid-state reaction method.Effects of the calcination and sintering atmospheres on microstructure,dielectric,piezoelectric,and ferroelectric properties of the ceramics were studied.The results of X-ray diffraction imply that all ceramics exhibit pure perovskite structure.SEM results show that the two different samples have different microstructures.The ceramics show similar dielectric constant-temperature curves with different depolarization temperatures.The ceramics prepared in the nitrogen atmosphere and those prepared in the oxygen atmosphere exhibit the mean grain size of 2.1 ?m and 1.0 ?m,the Curie temperature of 248 ? and 258 ?,the depolarization temperature of 76 ? and 87 ?,the remnant polarization of 27.2 ?gC/cm2 and 27.6 ?C/cm2.(2)The lead-free piezoelectric ceramics Bi0.5iNa0 sTiO3 were prepared.The air and nitrogen atmospheres were used separately during the calcination and sintering processes via a solid-state reaction method.All the ceramics exhibit pure perovskite structure.The ceramics prepared in the air atmosphere and those prepared in the nitrogen atmosphere exhibit the mean grain size of 1.3 ?m and 1.9 ?m,the activation energy values of 2.0 eV and 1.9 eV,the Curie temperature of 291 ? and 308 ?,the maximum polarization of 12.3 ?C/cm2 and 17.4 ?C/cm2,the residual polarization intensity of 11.0 ?C/cm2 and 13.7 ?C/cm2,the coercive field of 44.0 kV/cm and 47.8 kV/cm,respectively.(3)Based on the preliminary experiment,by changing the(Na0.5Bi0.5)0.94Ba0.06TiO3 preparation technology of the ceramic,which used in the process of presintering different presintering temperature,further study the presintering temperature of ceramic samples of phase structure,microstructure and electrical properties.The precursor powders were calcined at different temperatures.All ceramics exhibit pure perovskite structure.The ceramics with the calcination temperature of 600 ? and those with the calcination temperature of 900 ? exhibit the mean grain size of 1.7 ?m and 0.9 ?m,high relative density(>95%),the activation energy values of 0.8 eV and 1.3 eV,the Curie temperature of 272 ? and 243 ?,the maximum polarization of 31.7 ?C/cm2 and 35.9?C/cm2,the residual polarization intensity of 27.0 ?C/cm2 and 29.4 ?C/cm2,the coercive field of 32.7 kV/cm and 31.2 kV/cm,the piezoelectric constant of 97 pC/N and 113 pC/N,respectively.