Fabrication Of LiTaO₃-based Ceramics And Study On Its Micro-defects And Dielectric Properties

As a typical multifunctional material,LiTaO₃ has been used in many fileds such as filters,detectors and other electronic devices,due to its unique electrical properties.The dielectric properties of materials play an important role in promoting the miniaturization,lightweight and integration of electronic devices,which affects the performance of filters and detectors greatly.In recent years,the performance of LiTaO₃ single crystals has attracted considering attention from researchers,but there are few reports on microstructure and dielectric properties of LiTaO₃ ceramic materialsIn this paper,LiTaO₃ ceramics with different MnO₂ were obtained by pressureless and hot-pressing sintering,respectively.The effects of sintering method,pressureless sintering temperature,hot-pressing sintering atmosphere and MnO₂ content on the density,hardness,micro defects and dielectric properties of LiTaO₃-based ceramic were investigatedLiTaO₃-based ceramics?MLT-S?with 1-3 wt.%MnO₂ were fabricated by pressureless sintering.With the increase of MnO₂ content,the densification and vickers hardness of the ceramics increase.When the MnO₂ content is 3 wt.%,the maximum values are 92.6%and 650 HV,respectively.The LiTaO₃-based ceramic exhibits a homogeneous ceramic microstructure at the MnO₂ content is 3 wt.%,but a few second phases appear.With the increase of MnO₂ content,the number of oxygen vacancies in LiTaO₃-based ceramics increases first and then remains unchanged.It was shown by the dielectric properties versus frequency of MLT-S ceramics fabricated by different MnO₂ content at room temperature that the ?r of the ceramics increases with the increase of MnO₂ content,and the maximum value of 3MLT-S ceramics is 42;the tan? of ceramics first decreases and then increases,and the lowest value of 1.5MLT-S ceramic is 0.005.The variation trent of dielectric properties versus temperature of MLT-S ceramics fabricated by different MnO₂ content at 1 MHz indicates that the ?r increases with the increase of MnO₂ content,and the peak value of ?r of 3MLT-S ceramic is 518.2.5MLT-S ceramics were prepared by pressureless sintering at 1200?,1250?,1300?and 1350?.With the increase of sintering temperature,the density and vickers hardness of the ceramics first increase and then decrease,the maximum value are 89.2%and 495 HV at 1250?,and the microstructure is uniform and dense.It was shown by the dielectric properties versus frequency of 2.5MLT-S ceramics fabricated by different sintering temperature that with the increase of sintering temperature,the ?r of ceramics first increase and then decrease,the maximum value of ?r is 36 at 1250?;and tan? of ceramics changes little with temperature,the minimum value of tan? is 0.01 at 1350?.The variation trent of dielectric properties versus temperature of 2.5MLT-S ceramics fabricated by different sintering temperature at 1 MHz indicates that the peak value of ?r increases first and then decreases with the increase of sintering temperature,and the maximum value is 363 at 1250?.So,the 1250? is optimal sintering temperature under pressureless sinteringFurthermore,LiTaO₃ ceramic with 3 wt.%MnO₂ were prepared by hot-pressing sintering at different sintering atmosphere.The density and vickers hardness of the ceramics sintered in vacuum are 93.6%and 660 HV,respectively.There are many pores in the ceramic and the grain size is not uniform.The ceramics sintered in N2 have higher density and hardness,which are 98.5%and 790 HV,respectively.The porosity in the ceramic is obviously decrease,and exhibits uniform grain size.There is no second phase in ceramics under different sintering atmosphere.The ?r and tan? are 73 and 0.02,but the ?r and tan? are in vacuum are 53 and 0.03.So N₂ should be used in hot-pressing sinteringLiTaO₃-based ceramics?MLT-H?with different MnO2 content were fabricated by hot-pressing in N2 atmosphere.With the increase of MnO₂ content,the density and vickers hardness increase first and then decrease.When MnO₂ content is 2.5 wt.%,the maximum values are 98.9%and 799 HV,respectively.Meanwhile,the grain size tended to be uniform,showing a dense and uniform microstructure.When the content of MnO₂ is 3 wt.%,the second phase appears in the ceramics.In the LiTaO₃ grains of MLT-H ceramics,the domain structure is mainly non 180° domain.The number of oxygen vacancies in ceramics increases with the increase of MnO₂ content.It was shown by the dielectric properties versus frequency of MLT-H ceramics fabricated by different MnO₂ content that the ?r increases first and then decreases with the increase of MnO₂ content,and the maximum value of 2.5MLT-H ceramics is 83;the tan? increases with the increase of MnO₂ content,and the minimum value of 1MLT-H ceramic is 0.002.The variation trent of dielectric properties versus temperature of MLT-H ceramics fabricated by different MnO₂ content at 1 MHz indicates that the peak value of ?r increases first and then decreases with the increases of MnO₂ content,and the maximum peak value of ?r is 1973 when the MnO₂ content is 2.5 wt.%.