摘要
Glass-free MgO-based microwave dielectric ceramics(1-x)wt%(0.98 MgO-0.02 Al2O3)-x wt%LiF(x=0.5,1,2,3,4)were synthesized where LiF and Al2O3 were utilized as sintering additive and reinforcement phase in MgO matrix respectively.It was found that ion substitution is apt to occur between LiF and MgO,leading to the formation of oxygen vacancies and MgF2.Nevertheless,different from ordinary liquidphase sintering,morphologies of ceramics were distinctly altered with grains changing from polyhedron to sphere-like shape and densities underwent obvious decrease when excessive amount of LiF was introduced and we call it excessive liquid-phase sintering.Grain boundary weakening caused by this circumstance would exert an adverse effect on physical properties.Moreover,LiF addition dramatically reduced dielectric breakdown strength and altered the dielectric breakdown behavior of MgO-based ceramics,which is dominated by electrical breakdown mechanism.Combination of good properties were achieved in 1 wt%LiF modified MgO-based ceramics sintered at 950℃ which exhibited superior microwave properties(εr=9.56,tanδ=9.2×10^(-5),Qf=124,600 GHz),high flexural strength(184.5 MPa),high thermal conductivity(21.3 W/(m,K)),high coefficient of thermal expansion(-12 ppm/℃)and moderate electrical properties(Eb=35.9 kV/mm,r=4.9×10^(12) U cm).
基金
supported by National Natural Science Foundation of China(Grant No.11774366)
International Partnership Program of Chinese Academy of Sciences(Grant No.GJHZ1821)。
作者简介
Chi Zhang received his B.S.degree in Materials Science and Engineering from Southwest Jiaotong University in 2017.He is pursuing his Ph.D.in Materials Physics and Chemistry at Shanghai Institute of Ceramics,Chinese Academy of Sciences.His research mainly focuses on high-insulating materials and dielectric breakdown mechanism;Corresponding author:Ying Chen received her M.S.degree in Condensed Matter Physics from Shanghai University in 2003.She has been an associate professor at Shanghai Institute of Ceramics,Chinese Academy of Sciences since 2010.Her research mainly focuses on multiferroic magnetoelectric composite film and microwave tunable dielectric materials.Key Laboratory of Inorganic Functional Materials and Devices,Shanghai Institute of Ceramics,Chinese Academy of Sciences,588 Heshuo Road,Jiading District,Shanghai,201800,China,E-mail addresses:chenying@mail.sic.ac.cn;Xin Li is now an assistant engineer at Shanghai Institute of Ceramics,Chinese Academy of Sciences.He mainly focuses on preparation of functional ceramics and acceleration sensors;Haishen Ren received his Ph.D in materials sciences from the Chinese Academy of Sciences in 2018.He has been a Research Assistant at the Shanghai Institute of Ceramics,Chinese Academy of Sciences since 2018.His research focuses on Low-and High-temperature co-fired ceramics,special glass materials and high-performance dielectric microwave ceramics;Genshui Wang received his Ph.D.from Shanghai Institute of Technical Physics,Chinese Academy of Sciences in 2003,followed by Postdoctoral Fellow at Institute of Electronics,Microelectronics and Nanotechnology(IEMN)of the Universite de Valenciennes et du Hainaut Cambresis in France.He has been a professor at Shanghai Institute of Ceramics,Chinese Academy of Sciences since 2007.His research interests include the controllable synthesis of electronic ceramics and their applications in capacitors,sensors,and transducers;Corresponding author:Xianlin Dong received his Ph.D.from Shanghai Institute of Ceramics,Chinese Academy of Sciences in 1992.In 1996,he carried out cooperative research in the Department of Physics and Engineering,University of Tsukuba,Japan as a visiting researcher of JSPS.He has been a professor at Shanghai Institute of Ceramics,Chinese Academy of Sciences Since 1998.His research focuses on highperformance piezoelectric ceramics and devices,high energy storage medium materials and functional oxide thin films,Center of Materials Science and Optoelectronics Engineering,University of Chinese Academy of Sciences,19 Yuquan Road,Shijinshan District,Beijing,100049,China.E-mail addresses:xldong@mail.sic.ac.cn。
